[documentation] Les déclencheurs de diapause, et sortie de diapause |
Bienvenue invité ( Connexion | Inscription )
[documentation] Les déclencheurs de diapause, et sortie de diapause |
Thursday 26 November 2009 à 12:26
Message
#1
|
|
Myrmécomorphe Groupe: Contributeurs Messages: 5 633 Inscrit: 20/08/2007 Lieu : Armentières (59) Membre No.: 1 645 |
Un premier document sur les modes de déclenchement de la diapause chez les fourmis :
THE ANTS p.295 (Bert Hölldobler,Edward O. Wilson) CITATION(Bert Hölldobler,Edward O. Wilson : THE ANTS p.295) MEDIATION OF LARVAL DIAPAUSE : Colonies of most ant species in the north temperate zone undergo some form of diapause during the late fall and winter. The metabolic rate and locomotor activity slow down drastically and reproduction ceases. In the genus Camponotus, the species of which usually nest in fresh and decaying wood and hence are called carpenter ants, the adults and brood enter diapause in the cold season (Hölldobler, 1961). Similarly, most myrmicine species overwinter with larvae in the nest, and these immature stages also pass through a diapause of their own. In most organisms diapause is entrained by a shortening of the daily photoperiod, which is by far the most reliable "calendar" available. Wokers of Myrmica rubra have been proved use photoperiod (Brian, 1986), and there is no reason to expect otherwise for adults of ants generally. On the other hand a mystery remains. Ant larvae are hidden by the adults in soil or rotting vegetation, and thus live in permanent darkness. How do they measure the change in season and choose to enter diapause? Weir (1959) proved that fall ("serotinal") workers of Myrmica tend to induce diapause in terminal-instar larvae, whereas spring ("vernal") workers cannot. This result was achieved by keeping workers in the laboratory at the warm temperature of 25°C for 11 weeks after lengthy chilling to simulate in them the physiological state of wild spring condition. The "fall" workers could induce diapause ; the "spring" workers could not. Closely similar experiments were performed by Kipyatkov (1979, 1988) on M. rubra in the Soviet Union, with the same result. Weir further guessed that diet might be the key, since Myrmica workers are known to increase the proportion of protein in the diet as the season progresses, and dormant larvae have a higher nitrogen-to-car-bon content in their maconia and fat bodies than do nondormant larvae. When Weir fed spring workers a sufficiently increased amount of protein (by means of a pure diet of Drosophila), it turned out that they too were able to induce dormancy. Weir, after concidering the matter at length, remained uncertain whether the larval dormancy is true diapause in the purest sense, in other words a shut-down mediated by the endocrine system. Still, it qualifies as diapause in the broad sense that, once initiated, it is persistent in its effect, even at raised temperatures. Kipyatkov is in substantial agreement. In addition, he has provided evidence of a remarkable new volatile pheromone from spring workers that reactivates diapausing larvae and queens. Rien de bien nouveau : juste un petit rappel sur la complexité du déclenchement de la diapause et des influences perturbatrices que l'on peut avoir en élevage sur leur cycle naturel. PS : une belle petite traduction serait pas de refus. D'avance merci -------------------- |
|
|
Friday 27 November 2009 à 07:16
Message
#2
|
|
Cocon Groupe: Membres Messages: 294 Inscrit: 16/03/2007 Lieu : Toulouse Membre No.: 1 291 |
Insomnie, quand tu nous tiens...
Désolé grimmjoww ^^ Je me suis permis quelques largesses, mais elles ne devraient pas nuire au sens du texte. TRADUCTION : DECLENCHEMENT DE LA DIAPAUSE LARVAIRE : Les colonies de la majorité des espèces de fourmis des zones tempérées nordique subissent une forme de diapause durant le fin de l'automne et de l'hiver. Le niveau métabolique et l'activité locomotrice diminuent drastiquement alors que la ponte cesse. Chez le genre Camponotus, dont les espèces nichent habituellement dans le bois vivant ou en décomposition ce qui leur vaut le nom de 'fourmis charpentières', les adultes et le couvain entrent en diapause durant la saison froide (Hölldobbler,1961). De la même manière la plupart des espèces de Myrmicinae hivernent avec des larves dans le nid, ces stades immatures traversent eux aussi leur propre diapause. Pour la majorité des organismes la diapause est déclenchée par une réduction de la photopériode, qui est de loin le "calendrier" le plus sûr disponible. Il a été prouvé que les ouvrières de Myrmica rubra utilisaient la photopériode (Brian, 1986), et il n'y a pas de raison de s'attendre à autre chose de la part des fourmis adultes d'une manière générale. D'un autre côté un mystère demeure : Les larves de fourmis sont cachées par les adultes dans le sol ou la végétation en décomposition, vivant ainsi dans le noir permanent. Comment mesurent-elles les changements de saison et choisissent d'entrer en diapause ? Weir (1959) a prouvé que les ouvrières automnales de Myrmica ont tendance à induire une diapause sur les larves en stade terminal, alors que les ouvrières printanières ne peuvent pas. Ce résultat a été atteint en gardant les ouvrières à des températures chaudes de 25°C durant 11 semaines, après une longue réfrigération pour simuler l'état physiologique printanier en milieu naturel. Les ouvrières automnales pouvaient induire une diapause ; les printanières ne le pouvaient pas. Des expériences similaires furent entreprise par Kipyatkov (1979, 1988) sur M. rubra en Union soviétique avec les même résultats. Weir supposa que le régime alimentaire était peut-être la réponse, car les ouvrières de Myrmica sp. sont connues pour augmenter la proportion de protéines dans le régime alors que les saisons avancent et que les larves diapausantes ont un ratio azote/carbone dans leur meconium et tissus adipeux plus élevé que dans les larves non-diapausantes. Quand Weir nourrit les ouvrières printanières avec une quantité suffisante de protéines (grâce à un régime exclusif de drosophiles), il s'est avéré qu'elles étaient elles aussi capable d'induire une dormance. Weir, après avoir considéré la question un long moment est resté incertain : La dormance larvaire est-elle une vrai diapause au sens strict, en d'autre termes une interruption conduite par le système endocrinien ? Cependant cela reste une diapause au sens large, dans le sens où, une fois initié elle reste persistente dans ces effets même avec une augmentation des températures. Kipyatkov, en substance, tombe d'accord. De plus il a apporté la preuve d'une étonnante nouvelle phéromone volatile produite par les ouvrières printanières qui 'réactive' les reines et larves diapausantes. Ce message a été modifié par sipatte: Friday 27 November 2009 à 16:28
Raison de la modification: quelques petites modifs ;)
-------------------- "Pressé fortement sur ma droite, mon centre cède, impossible de me mouvoir, situation excellente, j'attaque.", Ferdinand Foch
"La guerre ! C'est une chose trop grave pour la confier à des militaires.", Georges Clemenceau |
|
|
Saturday 05 December 2009 à 14:39
Message
#3
|
|
(●ʘ╻ʘ●) ~ ♥ Groupe: Modérateurs Messages: 6 121 Inscrit: 17/08/2005 Lieu : Australie Membre No.: 284 |
Cher ami Soit, selon les espèces, les larves sont capables ou non de diapause. Certaines peuvent stopper leur développement et ralentir leur métabolisme pendant plusieurs mois, d’autres ne peuvent survivre à l’hiver... et alors ?
Chez les espèces ou les larves ne diapausent pas, les colonies arrêtent d’élever de nouvelles larves quand l’automne arrive pour éviter tout gaspillage. Mais en élevage, on est brutal sur l’entrée dans la diapause, on prend les colonies par surprise et on se retrouve souvent avec du couvain juste avant d’entrer dans la diapause. Tout ca peut se résoudre avec un éclairage naturel, une diminution progressive de la température, etc, mais fondamentalement ce n’est pas bien grave de perdre quelques larves en fin d’automne. A vrai dire en élevage, si on s’intéresse uniquement au couvain et aux ouvrières, la diapause est sans intérêt : la croissance de la colonie est plus rapide sans diapause et en mortalité on s’y retrouve (froid vs sur-activité) Maintenant si on a des reines dans les colonies, la donne est différente. La reine vit plusieurs années, et quand elle meurt, on perd la colonie aussi, c’est balot. Comprendre les mécanismes d’entrée en diapause, c’est pour ménager la reine que c’est intéressant. On pourrait tout a fait, couper les colonies en deux : mettre la reine au froid avec un petit groupe d’ouvrières, et laisser le reste des ouvrières/ couvain au chaud pour que ce dernier continue à se développer (comme si on faisait croire aux jeunes ouvrières né en hiver, qu’elles sont nées au printemps). Bref Toutes les reines présentes en France ne sont pas égales devant la diapause, on doit pouvoir dégager 3 types différents : - il y a celles chez qui le déclenchement de la diapause est relativement endogène : même si elle est conservée à température chaude pendant l’hiver, la reine est programmée pour se reposer 6 mois dans l’année, et elle le fait. C’est très flagrant chez certaines espèces de Lasius, Formica, Camponotus où l’activité cesse malgré nous au cours de l’automne. On ne peut pas tricher avec ces espèces là. Il y a tout intérêt à les accompagner dans leur diapause par une diminution de la température, pour pouvoir contrôler la sortie de diapause au printemps en augmentant la température (à défaut, on peut avoir des reines qui reprennent difficilement la ponte) - chez d’autres le déclenchement est plus extérieur, c’est la baisse des température, de la photopériode,etc, qui induisent un ralentissement d’activité. Conserver à conditions d’élevage constantes au cours de l’année, on n’observe pas de diminution de l’activité. Cette catégorie se divise en deux : les espèces qui subissent la diapause, mais qui n’en ont pas besoin physiologiquement et celles chez qui c’est nécessaire pour que la reine soit bien cyclée et vive vieille Savoir si une reine a besoin de diapause ou pas, n’est pas aisée. La question se pose pour les espèces qui ont des aires de répartition plus étendue que la France, et qui vivent également dans des régions sans diapause, du style Tetramorium caespitum qui est invasive en Floride. Dans les populations de nos régions, les reines sont sélectionnées pour leur résistance au froid, il s’agit de se demander aussi si il y a aussi certains génotypes qui tirent avantage d’une diapause, quand d’autres la subissent simplement. Soit pour une même espèce, savoir si dans certaines populations géographique, la diapause est utile et dans d’autres inutile ? Quand aux Myrmica, j’en ai élevé pour mon mémoire en conditions constantes sans dommages et au laboratoire on les maintient en activité toute l’année. Les reines vivent moins longtemps et la production de sexués est décalée. On peut se permettre ca, parce que les colonies sont populeuses et que les reines sont renouvelée par des accouplements en captivité. Pour ces espèces, il faut se demander si on préfère une reine qui vit vieille mais avec plusieurs mois d’inactivité par an, ou une reine qui vit deux fois moins longtemps, qui n'aura pas une production de sexués synchrone, mais dont on peut profiter toute l’année. Crematogaster scutellaris est grosso-modo identique en élevage. On peut avoir une idée des espèces dans ce cas de figure dans les papiers de Kipyatkov, ca concerne également des sp de Pheidole et Tetramorium en Europe bises |
|
|
Saturday 05 December 2009 à 18:41
Message
#4
|
|
Myrmécomorphe Groupe: Contributeurs Messages: 5 633 Inscrit: 20/08/2007 Lieu : Armentières (59) Membre No.: 1 645 |
Merci hugo
Je me doutai bien que des espèces qu'on trouve en Afrique (Messor barbarus, Aphaenogaster senilis, …) n'ont pas besoin d'une période de froid importante. Trois mois à 10° pour ces espèces est très certainement une rude épreuve plus qu'une nécessité. Mais effectivement, ça va mieux en le disant Es-tu vraiment sûr que l'absence d'une période froide pour les ouvrières des espèces de région froide ne réduit pas considérablement leur durée de vie? Mes questions concernent effectivement plutôt les espèces dont les reines ont manifestement besoin d'une pause dans leur ponte : - quels paramètres entrent en jeu dans le déclenchement de cette pause ? - avec quelle intensité ? - quels paramètres entrent en jeu dans le redémarrage des pontes ? On a quelques réponses ci-dessus, d'autres à venir j'espère … -------------------- |
|
|
Saturday 05 December 2009 à 21:15
Message
#5
|
|
(●ʘ╻ʘ●) ~ ♥ Groupe: Modérateurs Messages: 6 121 Inscrit: 17/08/2005 Lieu : Australie Membre No.: 284 |
CITATION Es-tu vraiment sûr que l'absence d'une période froide pour les ouvrières des espèces de région froide ne réduit pas considérablement leur durée de vie? J'ai pas dit ca. Les gens qui ont des métiers éreintants vivent en moyenne moins longtemps que ceux qui se la coulent douce. C'est sordide mais c'est pareil chez les fourmis. Quand on chauffe une colonie au dessus de l'optimum, quand on empêche les ouvrières d'avoir une période de repos, quand on donne des psychotropes à une reine pour qu'elle ponde plus... on accroit l'activité métabolique moyenne au cours de l'année et ca a bien sûr une conséquence sur le vieillissement. Mais la diapause est une période critique à dépasser, qui s'accompagne également d'une forte mortalité, surtout en élevage où on la maitrise mal. Quand bien même, pour l'élevage d'une fondation, on a une croissance globale bien plus rapide, si il y a une nouvelle génération tout les mois de l'année avec des ouvrières qui ne vivent que 6 mois, plutot que seulement 6 générations par an et des ouvrières qui vivent 1 an. Ca serait mathématique, si la reine venait pas mettre le bazar (.) Chez la plupart des organismes de climat tempéré, c'est la diminution de la photopériode qui est pointée du doigt comme la cause majeure d'entrée en diapause. Pour la sortie de diapause chez les insectes, c'est la température qui semble être la plus influente (peu importe la photopériode quand on est enfouit sous terre...) |
|
|
Saturday 05 December 2009 à 21:34
Message
#6
|
|
Myrmécomorphe Groupe: Contributeurs Messages: 5 633 Inscrit: 20/08/2007 Lieu : Armentières (59) Membre No.: 1 645 |
Un autre document très intéressant et complet sur le sujet (merci hugo ) :
Seasonal life cycles and the forms of dormancy in ants (Hymenoptera: Formicoidea) Vladilen E. KIPYATKOV CITATION Departmcnt of Entomology, Faculty of Biology, St. Petersburg University, Universitetskaya cmb. 7/9, St Petersburg, 199034, Russia; e-mail: vk@VKI280.spb.edu Received August 15, 2000; accepled August JO, 2001 Published October 2, 2001 Abstract. The forms of dormancy round in ants range from simple quiescence to profound diapause. Most tropical ants arc homodynamic and have no developmental arrests: ail ontogenetic stages [rom egg to pupa are present in their nests throughout the year. Sorne of thcm (quasi-heterodVl1amic species) have penetrated into the regions with wann ternperate climates but did not evolve real diapause. The developrnent of their brood ceases only at temperatures below the threshold of devclopment (consecutive dormancy) and ants overwinter in a quiescent (cold coma) stare suffering from more or less strong mortality. Most temperate ants, however, are truc helerO(~vnamic, i.e. they possess real winter diapause (prospective dormancy). In <!xogenous-h<!tcrodynamic species diapause in larvae and queens is facultative and arises in direct response to falling temperatures in auturnn, but diapause begins arter sorne delay and when temperatures are still weil above the threshold of development. The diapause in endogenous-heterodynamic species is ohligat(1)' at a co{ony {eve1 in a sense that it ensues sooner or later under any circurnstances. Their intrinsic broodrearing cycle 15 limited by an endogenous limer called a sand-g{ass device and 15 also controlled by environmental eues tempe rature and photoperiod (in sorne species), which can only advance or delay the onse! of diapause to sorne extent. Larval dormancy in these ants is facultative diapause induced by social influences of the nurse workers and temperature eues. Adult donnancy is ohligate diapause characterized by inactive state of avaries and al50 by inability of workers to rnaintain high growth rate and non-diapause development of larvac and normal egg production of queens. The adult and larval diapause in sorne endogcnous-heterodynamic species is quite stable even at high tempe ratures and long days but in many others diapause can easily be terminated in such circumstances. ln many anis, bath endogenous- and exogenous-heterodynamic, the diapause larvae in the last instar continue to feed and to grow slowly and can atlain significantly larger size before ovel"\~:intering, The diapause complction in temperate ant, is normally a resul! of cold reactivation, i.e. the winter exposure to low temperatures, which also leads to (1) the resturation of the colony's "spring physiology" and full capability to rcalize a new brood-rcaring cycle, and (2) the changes of the norm of reaction to photoperiod (gcncral 105S of sensitivity in spccies that have photoperiodic responses) and temperature (ability ta pro duce eggs and rear larvae without diapause at rather low tcmperatures that induce diapausc in summer). Seasonality, climate, temperature, photoperiod, developrnent, diapause, exogenous, endogenous, social, control, Hymenoptera, Formicoidea, Formicidae INTRODUCTION Despite extensive studies ofatthropod dormancy and seasonality during the last several decades, most ant specialists remained Îndifferent to this subject. As a result the papers specially devoted to phenology, diapause and seasonal cycle control are rather scarce in myrmecologicalliterature; more frequently the se questions are discussed only parenthetically and given less prominence than the main problem under consideration (for examples see the review of Brian 1977). In the fundamental modem treatise 'The Ants" by Hôlldobler & Wilson (1990) the seasonality of dcvelopment is not even mentioned. Our studies were, therefore, devoted to the elimination of this gap in ant ecophysiology and sociobiology. Since 1969 more than 70 ant species belonging to 21 genera and four subfamilies from different regions of the former USSR have been studied in our laboratory. We used two main research methods: laboratory experiments and field phenological observations. In experiments the colony fragments (more rarely the who le natural colonies) consisting of workers, queens (or a single queen in monogynous species) and the brood were used. They were kept in artificial plastic nests under different constant temperatures (or thermoperiods) and photoperiods. Our culturing methods allowed us to observe and to study in the laboratory all phases of ant annual cycle including the overwintering in a refrigerator under 3-5 oc. This research resuIted in a classification of the structural diversity of ant annual cycles, revealed the primary factors of their control and led to sorne ideas on the possible ways oftheir evolution (Kipyatkov 1981, 1993, 1994, 1996, Kipyatkov & Lopatina 2002b, c). The main purpose of this paper is to consider the types of seasonal development and the forms of dormancy found in ants in connection with the mechanisms oftheir control. This review is based on the results of our studies and also on data in the literature. MAIN TERMS AND DEFINITIONS The terms seasonal deve!opment and seasonal file cycle are traditionally used to designate the seasonal differences in the development and physiology of individuals of a species at different times ofyear (e.g., Danilevskii 1961). The annual cycle of development of a species is, therefore, a succession of the individual life cycles of different generations (in polyvoltine species), the whole life cycle of a single generation (in monovoltine species) or a sum of different parts ofthe life cycles of several successive generations (in semivoltine and perennial species). Ants are social insects and their colonies are not only perennial but usually even have unlimited life cycle i.e. are potentiaUy immortal unless environment becomes too adverse (Bourke & Franks 1995); adult ants (especially queens) also live for several years (HoUdobler & Wilson 1990). The brood and workers in an ant colony may ail belong to the same genetic generation (in monogynous species having a single queen in each colony) during several successive years (while the same mother queen is alive) or they may belong to different but overlapping generations (in polygynous species having several queens in each colony). But the seasonallife cycle of a colony has nothing in common with the differences between generations. Instead, it involves the regular seasonal changes in developmental paths, physiological states and behaviour of individuals of aU generations composing a colony. This is why the seasonallife cycle of an ant colony should be better referred to as the an nuaI cycle of deve!opment, physiology and behaviour (Kipyatkov 1993, 1996). In spring ants awake from the winter dormancy and begin their routine activity, the workers start to rear larvae (ifthe species overwinter with brood), a queen (or queens) begins to lay eggs from which new larvae originate, the larvae grow, pupate and bec orne new workers or alate reproductive females and males. The oviposition and brood development continue through the whole warm season until queens enter diapause and stop laying. Before the ons et of winter aU the eggs and young larvae develop into adults or up to a stage at which dormancy ensues and the colony moves to a overwintering place with diapause larvae or without brood. The workers also enter diapause in autumn and accumulate the nutrients in their bodies necessary for overwintering and early spring activity. Thus, each individual ant (queen, worker and ev en sorne larvae) can enter diapause and resume non-diapause activity several times in its life. This situation is unique for ants and other social insects with perennial colonies and only partly resembles extremely long perenniallife cycles found in a few non-social insect species (cf. Danks 1992). Roubaud (1922a, b, 1925) first distinguished homodynamic species of insects which have no diapause but only quiescence ("pseudo-diapause" of Roubaud) due simply to low temperature conditions and immcdiately resume their aetivity after the rise oftemperature and heterodynamic species possessing true diapause ("diapause vrais" ofRoubaud) that arises weil in advance of the onset of adverse conditions and cannot be easily tenuinated by the rise of temperature. This valuable dichotomy i5 used for the classification of ant annual cyclcs of development de5cribed below. 1 also follow Müller (1965, 1970) in distinguishing two main fonns of arrested development: consecutive dOl'mancy or qu;escence and prospective dOl'mancy or diapause. Ants have diverse fonns of dormancy ranging from simple quiescence to profound diapause (Tab. 1). Only larvae and adults can enter diapause; embryonic (egg) diapause and pupal diapause are unknown in ants as weil as in most other Hymenoptera (Danks 1987). Some authors (e.g., Tauber & Tauber 1981, Tauber et al. 1986) insisted on a narrower definition of diapause as "honnonally mediated state oflow metabolic activity". However, the known cases of arrested development in arthropods range from total cessation of activity to suppressed development with less extensive efl'ects on growth (Danks 1987). This appears especially truc for ants (see be10w) and 1 therefore prefer to follow Danks (1987) in using a wider and most appropriate definition of diapause that does not require low metabolic activity and growth arrests, but only definitive suppression of development or reproduction. Another tenu, cold reactivation (Danilevskii 1961), used in this paper needs some comments. Temperature evidently plays multiple roles during insect diapause which are not yet completely understood; moreover, the diapause-development responses are not limited to the effects oftemperature and in fa ct can be much more complex (see Danks 1987, Hodek & Hodkova 1988). In particular, the role of low temperatures in termination of diapause as weil as the relevance of the tenn "cold reactivation" itself have been disputed by sorne authors (Hodek & Hodkova 1988, Zaslavski 1988, Hodek 1996). Although their arguments seem to be very sound in regard to the proximate causes of the diapause termination itself, 1 still find it appropriate to use the tenn "cold reactivation" to describe the apparent effects the overwintering at cool temperatures on an ant colony, namely, the restoration of colony's "spring physiology" and full capability to realize a new brood-rearing cycle (to be detailed below). As applied to ants 1 employ this term in addition to commonly used Andrewartha '5 "diapause development" (Danks 1987) and Hodek 's "diapause eompletion" (Hodek 1983, 1988, Hodek & Hodkovâ 1988) because the expression "cold reactivation" helps to emphasize in the best way the restoration of colony's spring physiological state rather than simply diapause completion. HOMODYNAMIC DEVELOPMENT Most ant species living in the tropics and warm subtropics have homodynamic seasonal development (Kipyatkov 1993, 1996). Ali ontogenetic stages from egg to pupa are always present in their nests, which means that development continues without any arrests throughout the year (Tab. 1). However, significant seasona1 variations in the abundance of certain brood stages and especially of the winged reproductives can usually be observed. For example, in Cataulacus guineensis in tropical Africa the number of the brood has two maxima in May and in September; alates are numerous in nests from July to October and are absent during other months (Ackonor 1983). The larvae of alates of Campono/us sericeus in Tndia develop from October to July and the nuptial t1ight takes place in September-October (Basalingappa et al. 1986, 1989). The seasonality of alate production has a1so been reported for Anoplolepis longipes in Papua New Guinea (Baker 1976) and in the Seychelles (Haines & Haines 1978), Camponotus detritus in the Namib desert (Curtis 1985), Pseudomyrmex sp. in Texas, USA (Baldridge & DeGraffenried 1988) and for many species of Neotropical anny-ants (Schneirla 1977, Rettenmeyer et al. 1983). The proximate causes of this seasonality in tropical ants are unknown. Uninterrupted homodynamic development was also observed in prolonged laboratory experiments under optimal temperatures in tropical ants Tetraponera anthracina (Terron 1977) and Monomorium pharaonis (Peacock & Baxter 1949, 1950, Peacock 1950b, Peacock et al. 1955, Petersen Braun 1975, 1977). Our experiments revealed the homodynamic type of development for three tropical species M pharaonis collected in St. Petersburg, Pheido/e sexspinosa from Tonga Archipelago and Tetramorium semillimum from the Seychelles. These species were kept in the laboratory during 1.5-2 years under various ecologically feasible conditions (temperature from 18 to 25 oC, photoperiods from lOto 16 hours of light per day) and incessant development without any sign of arrest was invariably observed. However, when colonies of Pharaoh's ant IVl pharaonis were kept at Temperatures close to or below the threshold ofdevelopment, which is about 17.7-17.8 oC (Kipyatkov & Lopatina 2002a), the mortality of brood and workers became too high and the colonies died out in a month. This finding is in good accordance with the fact that Pharaoh's ant occurs in Europe only in well-heated buildings (Bemdt & Eichler 1987). Unfortunately, other tropical ants are still unexplored in This respect. It is well known, however, that true tropical insects are unable to survive long at temperatures near or below the threshold for development and especially below the cold coma point i.e in the state of quiescence (Leather et al. 1993). Thus, most homodynamic tropical ants are not preadapted to cold weather and wou Id not survive even in warm temperate regions. QUASI-HETERODYNAMIC DEVELOPMENT The term quasi-heterodynamic can be applied to tropical ants that are adapted to exist in the regions with co Id winters but unlike true heterodynamic (see below) species do not have real diapause (Kipyatkov 1996). In optimal conditions the egg-Iaying oftheir queens and the development of their brood can proceed indefinitely and cease in nature only at Temperatures below the threshold of development (consecutive dormancy). The colonies ovenvinter in a quiescent (cold coma) state suffering from more or less strong mortality (Tab. 1). These species difier from true homodynamic ants only in this ability to survive somehow during cold winters. Several examples are described below. The red and black imported fire ants, Solenopsis invicta and S. richteri, were accidentally introduced into the United States from South America about 60 and 80 yeaTs ago, respectively, at the port of Mobile, Alabama (Lofgren 1986). Today, the red imported fire ant is distributed throughout most of the southeastern United States and the black imported fire ant is primarily restricted to northem Alabama and Mississippi and southern Tennessee (Lofgren 1986). Thus both species now occur in the regions with relatively cold winters. In fact they are homodynamic in the Southem United States since ail developmental stages occur in their nests throughout the year, although the amount ofbrood can be very low during mid-winter(Markin & Dîllier 1971, Horton & Hays 1974, Lofgren et al. 1975). However, in the northern parts of the fire-ant range, oviposition in colonies ceases during the coldest period ofthe winter and most larvae and pupae disappear (Markin et al. 1974, Lofgren et al. 1975). As long as the lower threshold oflarval development in S. invicta 15 about 17 oC (Porter 1988) many larvae (and also adult workers) may perish during the winter in northem populations ofthis species. Such wintermortality ofworkers is documented for S. invicta (e.g., Morrill 1977, Morrill et al. 1978). The Argentine ant, Linepithema humile, from South America has infested many territories ail over the world. The seasonallife cycle of tbis species studied in the South of Califomia, USA (Markin 1970) and in the South of France (Benois 1973) appeared rather similar to that ofthc fire ants. Only a few larvae (mainly small) and very few eggs can be found in the nests of l. humilis during the winter when adults make up more than 90% of colony biomass. In summer the brood constitutes about 50% of the biomass but in October it quickly declines and reaches a minimum by December. The primarily tropical army-ants of the genus Neivamyrmex in northem parts oftheirrange exist in a temperate climate with rather cold winters. According to the observations ofSchneirla (1958, 1971) in autumn when nights grow cooler these noctumal ants cease foraging. Then the lack of food forces the queen to stop laying, the workers destroy the remaining brood and the colony, comprising only adult ants, passes the winter in a shelter. In spring when temperatures rise the queen starts laying and the colony gradually restores the periodicity ofbrood-rearing and nomadic behaviour typical of the summer season (Schneirla 1963, 1971). Schneirla postulated the direct int1uence of low temperatures on the development of these ants. However, this statement has never been tested experimentally. We have studied the quasi-heterodynamic development in three species of myrmicine ants. Pheidole pallidula occurs in South Europe, the Caucasus and Middle Asia (Dlussky 1981); the range of P. fervida includes South-East Asia, lapan, Southem Kurils and the South of Primorie (Kipyatkov & Lopatina 1987, Kupyanskaya 1990). In Primorie P. fervida is likely to have persisted from the Tertiary when the climate was much warmer (Kupyanskaya 1990). In experiments on both Pheidole species (Kipyatkov 1993, 1996) the queens laid eggs and the larvae continued to develop and pupate uninterruptedly under any temperature above the lower developmentaI threshold. Thus, any form of diapause 1S absent in these ants. We have observed incessant and unlimited development in their colonies at optimal temperatures of25-28 oC during more than two years. In P. pallidula from Turkmenistan oviposition and larval development did not cease at 20 oc. After temperature decreased below the developmental threshold, which is about 18 oC in this species (Kipyatkov & Lopatina 2002a), the queens still continued to lay but the eggs did not develop, prepupae and pupae began to perish and ail the brood gradually died out. The overwintering ofthis species without brood was confirmed by our field studies in Turkmenistan and by the observations of Passera (1977) in Southern France. P. fervida, appeared to be better adapted to the rather severe winters of the Southem Primorie because its brood peri shed only partially during artifieial overwintering. After temperature decreased up to 10-12 OC in an experiment the workers began to dismember and diseard the pupae and prepupae and gradually destroyed ail of them. The ants overwintered, therefore, with eggs and larvae of ail instars. However, sorne proportion of eggs and young larvae died out during the artifieial overwintering, whereas older larvae overwintered successfully (Kipyatkov & Lopatina 1987). In Monomorium kusnezovi from Turkmenistan (Kipyatkov 1996) the growth and pupation of larvae continued without delays at ail temperatures above the threshold of development (between 20 and 21.5 oC for eggs, larvae and prepupae Kipyatkov & Lopatina 2002a). Thus, the larvae of this species have no diapause. At 20 oC and below the larvae ceased to grow but the queens continued to lay eggs. Therefore, the ant colonies contained eggs and larvae of ail instars before the artificial overwintering. Most eggs died during overwintering but larvae survived more successfully. The overwintering of M kusnezovi larvae was a150 confirmed by our field observations in Turkmenistan (Kipyatkov 1996). TRUE HETERODYNAMIC DEVELOPMENT Most temperate ants are true heterodynamic, i.e. they have a period of prospective donnancy (winter diapause) in their annuallife cyc le. However, heterodynamic development has been found in sorne tropical species as weIl. For example, ail five species of Rhytidoponera impressa group widespread in the forests of East Australia were found to have a distinct seasonality of development: only sm ail and medium size larvae and very rarely sorne eggs but no large larvae and pupae are present in their nests du ring the winter months, this seasonality being clear-cut both in the tropical and subtropical regions of Australia (Ward 1981). Preno/epis imparis in the northem part ofFlorida, USA (Tschinkel 1987) and Pozvrhachis vicina in the wann subtropics of China (Chen & Tang 1989, 1992) are also heterodynamic. As long as seasonality of the environ ment is usually quite apparent in the tropics, heterodynamic deveIopment with true diapause might be very common in tropical ants. Unfortunatcly, the data are still very scarce. Recent investigations give ever more evidence that various forms of donnancy and diapause are widespread phenomena in tropical and subtropical insects but the factors controlling donnancy in these species are as yet insufficiently known (Denlinger 1986, Danks 1987). It is worth emphasizing that heterodynamic development can serve as a preadaptation for survival during cold winters and facilitate the expansion of sorne tropical ants to temperate regions (Kipyatkov 1993, 1996). In a pioneering study oflife history evolution in social insects Oster & Wilson (1978) primarily concentrated on the scale and timing of the allocation of resourccs between worker and sexual production. They distinguished three main stages in a colony's life cycle:foundation stage when the solitary queen attempts to start its colony, ergonomie stage in which the colony grows by producing all-worker broods for a number ofyears, and reproductive stage in wich the colony each year produces a mixture ofworkcrs and sexuals. For the perennial species, such as ants, Os ter & Wilson (1978) predicted so-called "bang-bang" strategy which maximizes colony's fitness (sexual production) by altemation ergonomie and reproductive phases within each year. The ergonomie phase within each season should be as long as possible sa that more workers are available to raise the largest number of sexuals during the second part of the year. Such seasonal switches to sexual production resulting in clear oscillations in numbers of worker present in a colony were indeed observed in several species, such as So/enopsis invicta in the USA (Tschinkel 1993). However, the perennial colonies also have to invest in workers to promote winter survival and subsequent reproduction. Considering this constraint Oster & Wilson (1978) predicted that the switch to producing sexuals should occur later within a season as the colony overwintering survival rise. Since then little attention has been paid ta the role of seasonality in life history evolution in ants (e.g., Bourke & Franks 1995). Recently, the thorough analysis of literature and own data collected during many years of field work allowed Kipyatkov (1996) to conclude that most temperate ants evidently differ in seasonal timing ofworker and sexual production from the predictions of Oster and Wilson. First, most species raise their alate reproductives not in la te summer after the worker brood is already produced, but quite the reverse - just after the overwintering. In sorne ofthem sexuals originale From the first egg portion laid by queens in early spring. This group comprises species belonging to the tribe Fonnicini (generaAlloformica. Cataglyphis, Formica and Proformica) and the generaDolichoderus and Pogonomyrmex (Kipyatkov 1996). Another, much larger group consists of ail other temperate species in which alates develop from the overwintered larvae (Kipyatkov 1996). Anyhow, the rcaring of sexuals always precedes the period of worker production in an annual cycle of most temperate ant species. The second departure From the predictions of Oster and Wilson is that the production of sexuals is al ways accompanied by rearing of workers which can emerge even in greater numbers than winged reproductives (Kipyatkov 1996). It means that a complete switch from worker to alate production does not in tàct occur. Thus, most tcmpcrate ants use the strategy ofjJreceding production of sexua/s in their annual cycle (Kipyatkov 1996). This strategy demands that the colony's annual cycle should be organized in a way to maximize the quantity of diapause larvae and new workers produced by the end of each brood-rearing season; these workers will facilitate colony's winter survival and will rear alate females and males from overwintered larvae or from eggs next spring. For this purpose the broodrearing should start in spring as carly as possible and continue as long as possible. At the same time the brood stages and adults present in the nest by the beginning ofwinter should be capable of overwintering. To resolve this problem the temperate ants should evolve appropriate torms of winter donnancy and efficient mechanisms controlling its onset and completion at the proper time (Kipyatkov 1993, 1996). Temperate ants use two main seasonal strategies ofbrood-rearing (Kipyatkov 1996, Kipyatkov & Lopatina 1995, 1996a, b ). The most widespread Îs the strateg)J ofprolonged brood-rearing distinguished by delaying development of a large proportion of larvae (so-called slow brood) which continue to grow in autumn, overwinter in diapause and pupate during the next summer; thus, only some larvae develop from egg to pupa within the same summer season without overwintering (so-called rapid brood). The ofprolonged brood-rearing has several evident advantages important for adaptation to temperate and boreal climates (Kipyatkov 1993, 1996): (1) the larvae can be reared from early spring up to late autumn thus utilizing the whole warm period of a year; (2) the quantity ofrapid brood can be changed to adapt to long-term and short-term climatic variations and to the duration of the wann season; (3) the development oflarvae can be extended to two or even three summer seasons. (je rajouterai la Fig. 1) Fig. 1. Rcpcated induction and tcrmination of larval diapause in Iwo laboratory colonies of Tapil/oma karavaievi co1!ected in SUlTlmcr 1989 in T urkmenistan as a rcsult of successive changes of temperature regimes during a period of three years. The absence of pupae in a colony indicates that larvac are in diapause. (je rajouterai les Fig. 2 si utile) Fig. 2. Repeated induction and lermination of larval diapause in Iwo laboratory colonies (A and B ) of TetramorÎum jacoti from South PrimoTie (near Vladivostok) by successive alterations of temperature. Start of experiment on 17 Septembcr. The numbers of prepupae and pupae present in a colony al each cens us date are depieted. Sinee the prepupal stage lasts only several days, the absence of prepupae in a colony is a good evidence that larvac do nol pupale. Two structural types of annual cycles have been distinguished among heterodynamic species with prolonged brood-rearing (Kipyatkov 1993, 1996). In Aphaenogaster type the larvae enter diapause at the end of summer but the queens have no diapause and do not cease laying until the late autumn; therefore, not only diapause larvae but also eggs and young larvae overwinter and survive, at least partially, during the winter (Kipyatkov & Lopatina 1990). Ants with this type of cycle are apparently restricted to the subtropics and the southernmost regions of the temperate zone. lt was discovered in ail hitherto studied species ofAphaenogaster (Kipyatkov & Lopatina 1990) and in a few species of Leptothorax, A/essor, Monomorium, Po/yrhachis, Tapinoma and Temnothorax; (Kipyatkov 1993, 1996). Most species with prolonged brood-rearing have the seeond structural type of annual cycle Myrmica type. They ail have winter diapause both in larvae and adults and overwinter without eggs but only with diapause larvae of one or several in stars depending on species (Kipyatkov 1993, 1996). According to the stages in whieh larvae can enter diapause five species groups have been distinguished (Kipyatkov 1996): (l) speeies with diapause in early (1-3) instars (Lepisiota, Plagiolepis, Tapinoma, sorne Camponotus; full number of instars - 5), (2) species with diapause in middle (2-4) instars (Camponotus s. str.), (3) species with diapause in the two last (3-4) instars (Harpagoxenus, Leptothora-r s. str., Messor), (4) species with diapause in a final (usually the third) instar (Diplorhoptrum, Leptanilla, Monomorium, A/yrmica, Tetramorium), (5) species with diapause in all instars (Crematogaster, Lasius, Paratrechina, s.g. Tanaernyrmex of the g. Camponotus; full number of instars -5-6) (je rajouterai les Fig. 3 si utile) Fig. 3. Internally Iîmited intrinsic cycle of oviposition in Myrmica rubra queens in cultures collected in spring in Belgorod region and kept under Iwo temperatures and Iwo photoperiods (according to the data of Kipyatkov 1979). Start of experiment on 17 May. Each line - the average value for 4 queens in separate cultures. Evidently, short days and lower ternperature decreased the egg production and advanced the onset of diapause in queens. (je rajouterai les Fig. 4 si utile) Fig. 4. Specifie and geographic differences in the length of the intrinsic seasonal cycle of rapid brood production in A(vrmica rllginodis (A) and A(vrmica rubra ( B ) (aceording to the data of Kipyatkov & Lopatina 1997a). Ants were collected in early spring in Belgorod and St. Petersburg regions and cultured under long days (20 h) and 20 oc.Start of experiments 13 April (Belgorod), 2 June (St. Petersburg). Each line the average value for 4 experimental cultures. The cultures of A1. mbra had significantly longer period of pupation and produced more rapid brood pupae th an M. ruginodis cultures. M. rubra cultures From northern population (SI. Petersburg) had much shorter cycle of rapid brood-rearing and produced significantly less pupae in comparison with cultures from southem population (Belgorod). M. ruginodis cultures From St. Petersburg did not produce any rapid brood al all. The strategy of concentrated brood-rearing is employed by ant species with another struetural type of annual eye\es whieh 1 cali Formica type (Kipyatkov 1993, 1996). The devclopment of ail brood stages is restricted to the warm season in these ants. Only queens (and also workers) are able to diapause. Larvae have no dormancy and ail finish their development during the summer, ail new workers emerge from pupae until autumn cold weather and ants overwinter, therefore, entirely without brood. According to our observations and published data this strategy is characteristic for ail genera of the tribe Formicini (Al/ojbrmica, Cataglyphis, Formica, Projàrrnica) and for sorne species of the genera Dolichoderus, Pogonomyrmex, Panera and Prenolepis (Kipyatkov 1993, 1996). The onset of diapause in queens is a eentral point in the cycles of Formica type becausc it determines the moment after which new eggs do not appear, the brood gradually vanishes and the ants begin to prepare for overwintering. Queen diapause should not occur too early because it would not allow ants to use a part of the warm season for brood-rearing. At the same time if diapause ensues too late many larvae and pupae would not manage to finish their development and would perish due to low temperature. Evidently, the strategy of cO!1centrated brood-rearing is only appropriate for temperate and bore al ants in combinatio!1 with very fast brood development, allowing them to rear sexuals and new workers from eggs during a short warm season. In fact among tcmperate ants Formica speeies have the shortest developmental times and thcir dcvelopment is more temperature dependent, whieh allows Formica workers to rear the brood much faster at higher temperatures (Kipyatkov & Lopatina 2002a). Among ants inhabiting the temperate zone and adapted to cold winters two main groups can be distinguished aceording to the nature of dormancy and the type of seasonal cycle control: exogenous- heterod.vnamic and endogenous-heterodynamic (Kipyatkov 1993, 1996). EXOGENOUS-HETERODYNAMIC SPECIES In ants belonging to this group winter diapause in larvae and queens is facultative and arises in direct response to suboptimal temperatures in the autumll, but unlike simple quiescence in quasiheterodynamic species this diapause begins when temperatures are still weIl above the threshold of development. Ailother important property is that the diapause ensues not immediately following the temperature fall but after sorne delay and is reversible, Le. may be ended by reentering the optimal temperature range, also after a delay (Tab. 1). We have found diapause ofthis kind in several speeies of the genera Diplorhoptrum, Messor, Monomorium, Tapinoma and Tetramorium which are limited in their distribution to southem regions of the Palaearetie region, i.e. they live in rather warm temperate elimates (Kipyatkov 1993, 1996, Kipyatkov & Lopatina 2002b ). These species are also remarkable by their ability for continuous and unlimited development under optimal temperatures, behaving as true homodynamic species in these eircumstances. In our experiments several eolonies ofthese speeies were kept at temperatures above 25 oC or under daily thermoperiods of20/30 oC for more than two years and during the whole period queens continued to lay eggs, larvae emerged from eggs, grew and pupated without any delay or any changes for the worse in colony viability (Kipyatkov 1993, 1996, Kipyatkov & Lopatina 2002b ). At the same time, at suboptimal temperatures, i.e. below 23-25 oC but weB above the lower threshold, development ceased aftcr a short period. Iftemperatures rise after that, development will soon reeommence, but it may be blocked again by the fall oftemperature and then be resumed in response to a new temperature increase. We succeeded in repeating such alterations with the same ant colonies several times with similar results (Kipyatkov & Lopatina 2002b ). Three examples are given below. When summer colonies of Tapinoma karavaievi from Turkmenistan were kept at 28~30 oc or daily thennoperiod of20i30 oc they displayed continuous development for months, but at 25 oC, i.e. weIl above the threshold of development, which is about 20 oC (Kipyatkov & Lopatina 2002a), the larvae eeased to pu pate in 1-2 months and then resumed development only after the restoration of optimal tcmperature conditions, not immediately but after a delay of a month or more; the se succcssive changes could be repeated over and over again (Fig. 1). Since this polygynous species has an annual cycle of the Aphaenogaster type, queens never stop laying except at too low temperatures and, thus, eggs are a\ways present among the brood. Another Turkmenian species, Monomorillm ruzsftyi, has a lowerthreshold for larval development of21.8 oC (Kipyatkov & Lopatina 2002a), but its larvae ceased to pupate in summer at 23~25 OC whereas under 27~28 OC or a thermoperiod of 16/30 oC the new pupae appeared in colonies for many months. A third example is the repeated induction and termination of larval diapause produced in two colonies of Tetramorium jacoti from South Primorie (near Vladivostok) by successive alterations oftemperature (Fig. 2). Another important feature of exogenous-heterodynamic species is the distinct change of their norm of reaction to temperature during overwintering as a result of cold reactivation. In spring oviposition and development begins in their colonies at thrcshold temperatures as a result of the absence of diapause. (je rajouterai les Fig. 5 si utile) Fig. 5. Scasonal changes of intrinsically limited oviposition period in qucens of Formica aquilonia From St. Petersburg region (according to the data of Kipyatkov & Shenderova 1989). Samples of queens and workers were collected from natural nests on five dates during May-September (from 4 to 14 queens per date) and cultured in laboratory at 25 cc and long days (20 h) until the queens stoppcd egg-Iaying. The later in the season samples were collected. the lowcr was the pcrccntage of quecns still laying eggs after the collection and the shorter was the mean length of their oviposition period. After natural overwintering or after exposure in a refrigerator to 3-5°C during 2-3 months the development and pupation oflarvae recommenced and proceeded for a long period at 20°C and even at 18°C (in sorne Tetramorium) in all species studied (Kipyatkov 1993, Kipyatkov & Lopatina 2002b ). This ditTerence in the nonn ofreaction to temperature, which can be easily revealed in experiments, is another indication of the existence of diapause in exogenousheterodynamic species. ENDOGENOUS-HETERODYNAMIC SPEClES Most ants inhabiting the temperate zone and ail northern species belong to this group. Their diapause is obligatory al a colony level, i.e. it is mostly due to factors internai for the colony and no external conditions can prevent the definitive cessation of oviposition and development. Even at long days and optimal temperatures, including the daily thennoperiods which are the most favourable tempe rature conditions for ants (Lopatina & Kipyatkov 1993, 1997), queen egg-laying capacity and worker ability to rear larvae without diapause tend to decline step-by-step in colonies ofthese species until oviposition and larval development stop and diapause ensues sooner or later as a result of an endogenous timer effect (Tab. 1). This timer mechanism, internai for the colony, was called sand-glass device to depict the gradualloss of colony's capability to produce eggs and to rear larvae without diapause (see Kipyatkov 1993, 1996, Kipyatkov & Lopatina 2002c for details). Thus, a colony of an endogenous-heterodynamic species has an internally limited (by a sandglass device) intrinsic seasonal cycle of brood-rearing. Such an endogenous physiological cycle in constant laboratory conditions was first observed in A~vrmica by Brian for worker (1953) and queen (Brian & Hibble 1964, Brian & Kelly 1967) oviposition, and then for rapid brood production (Brian 1957, 1962, 1963). Similar results were also obtained for Camponotus herculeanus and C. Iigniperda (Hôlldobler 1961), several Leptothorax species (Cagniant 1968, Plateaux 1970, 1986, Espadaler et al. 1983, 1984), Plagiolepis pygmaea (Passera 1969) and Cataglyphis cursor (Cagniant 1979, 1980). In our experiments internally restricted cycles of queen oviposition and/or Iarval development in constant laboratory conditions were found in more than 60 species ofthe genera Aphaenogaster, Camponolus, Catag~vphis, Crematogaster, Formica, HGlpagoxenus, Lasius, Lepisiota, Lepfothorax, Mania}, MvrmÎca, Plagiolepis, Ponera, Pro{ormica and Tapinoma (Kipyatkov & Shel1- derova 1990, Kipyatkov 1993, 1994, 1996, Kipyatkov & Lopatina 1993, 2002c, Lopatina & Kipyatkov 1990, 1993). It was then found that the intrinsic length of colony's annual cycle ofbrood-rearing differed not only between close species but also between geographical populations of the samc species, which reflects their adaptations to local climate conditions (Kipyatkov & Lopatina 1997a,b ). Examples are shown in Figs 3-6. The best evidence for the endogenous and obligatory nature of colony diapause was provided by experiments with free choice by ants of the preferred temperature. In the first one (Kipyatkov & Shenderova 1986) two smal1 colonies of Formica polyctena were kept from early spring in nests with a hOlizontal temperature gradient From 5 to 40 oC in which ants were pennitted to make a free choice. A normal seasonal cycle of queen oviposition and larval development was observed in both colonies, during which ants with brood concentrated in parts ofthe nests with temperatures of20-30 oc. In August Queens stopped laying and ants began to move gradually to the cooler parts ofthe nests, finishing the brood-rearing process. The length ofthe brood-rearing cycle in experimental colonies appeared to be just the same as in nature as weil as in colonies simultaneously maintained in the laboratory at constant temperature of 25 oC (Kipyatkov & Shenderova 1986). Thus, the seasonal cycle of queen oviposition is compietely limited in this species by sorne internal factors and cannot be extended even in favourable conditions. Similar results were later obtained for several endogenous-heterodynamic species in our prolonged experiments in nests with horizontal tempe rature gradients (Kipyatkov 1994, 1996). (je rajouterai les Fig. 6 si utile) Fig. 6. Extremely prolonged production of rapid brood pupae in Myrmica rubra (A) and l'vlvrmica ruginodis ( B ) cultures collected in spring in Belgorod and St. Petersburg regions and maintained under long days (20 h) and aboye-optimum temperature 25 oC (according 10 the data of Kipyatkov & Lopatina 1997a). Start of experi· ments 13 April (Belgorod), 2 June (St. Petersburg). Eacb li ne ~ the average value for 4 experimental cultures. Even under such high temperature tha! strongly provoked development and pupation of larvae ant cultures from nonhcm population (St. Petersburg) had shoner cycle of rapid brood-rearing and produced less pupae in comparaison with cultures from southern population (Belgorod). Another confirmation for the endogenous nature of diapause control came from the observations of the spontaneous rhythms of oviposition and development in colonies of many ant species maintained under constant laboratory conditions for a long time: the egg-Iaying of queens and the development of larvae first ended, and then resumed after longer or shorter intervals, and these periods of direct development and of diapause could be repeated. Such a rhythm was first described by Hol!dobler (1961) in C. herculeanus and C. ligniperda. During inactive periods of the cycle these ants formed dense aggregations in the nest together with larvae in diapause, which were fed only a little at that time, and the workers of C. herculeanus even closed the ne st entrance then with a plug made oflitter. According to the observations of Plateaux (1970) in L. nylanderi development in the overwintered colonies at 24-25 oC proceeded during 90-100 days and then the obligatory period ofrest ensued and lasted for not less than another 100 days; after this diapause stage development could restart. ln our long-term experiments the spontaneous rhythms of oviposition and development were found in al! endogenous-heterodynamic species that we studied, namely in the genera Aphaenogaster, Camponotus, Cataglyphis, Crematogaster, Formica, Lasius, Lepisiota, Leptothorax, Myrmica and Plagiolepis. In diapause ant colonies kept under conditions identical to those in which the diapause has ensued a new developmental cycle could begin after a few weeks or after several months, and sometimes after almost a year. Oviposition and pupation continued for sorne time, but then a graduai decline was observed, and finally development became arrested again (Kipyatkov 1993, 1994, 1996). This phenomenon was most thoroughly explored in the red wood ants Formica aqui/onia and F polyctena: the data for several dozens of experimental cultures of each species maintained at various constant temperatures and photoperiods for 1-5 years were obtained and analysed (Kipyatkov & Shenderova 1989, 1990). In nests with horizontal temperature gradients we observed even more distinct spontaneous rhythms of oviposition and development which were closely associated with changes in the thermopreferendum: during periods of direct development ants kept their brood in chambers with sufficiently high temperature, and during periods of diapause in cool chambers (Kipyatkov 1993, 1994, 1996). There was considerable variation in the duration ofperiods of direct development and diapause in different experimental colonies and within the same colony. Furthermore, there was no coordination with the natural change of seasons. Ali this clearly indicates the endogenous nature of observed rhythms and the absence of external synchronizers (Kipyatkov 1993, 1994). This situation seems to be very similar to that found in sorne non-social insects which diapause as adults in which alternations of ovipositional arrest and resumption of oviposition can also be repeated in constant conditions (Hodek 1979, 1983). After analysing the available data Hodek (1998) came to the conclusion that this rhythmic alternation in the bug Aelia acuminata is endogenous and may be governed by internai timer(s), which is clearly analogous to my idea of a sand-glass device in ants. It is premature to discuss possible physiological mechanisms underlying these spontaneous rhythms. It should only be added that the available data distinctly demonstrate a rather complex nature ofthe sand-glass devicc in ants, which includes not only sorne unknown physiological mechanisms operating inside the bodies of individual ants but also a set of intricate social mechanisms functioning among individuals in a colony which control the onset and the end of diapause (Kipyatkov 1981, 1996, Kipyatkov et al. 1997a,b, Kipyatkov & Lopatina 1999). The latter mechanisms have so far been much better studied and understood (see below). It should be emphasized. however, that in most endogenous-heterodynamic ants, especially in species occurring in the northem regions of Palaearctic, after the spontaneous completion of diapause in the laboratory the reproduction and development are never as perfect as after nortnal overwintering al low temperatures: the productivity of Queens is low, not aIl overwintered larvae pupate and there is no rapid brood at aIl. Such a peculiarity of spontaneous resumption of development was tirst recorded by Plateaux (1970) in L. nylanderi. In our experiments we observed this phenomenon in ail northem species studied. After each brood-rearing cycle under constant conditions the indices ofproductivity decrease steadily, the number ofpupae produced and the number of ants in a culture gradually declines, their viability diminishes and tinally they ail die. In most prolonged experiments with red wood ants we sometimes addcd pupae fYom other colonies in order to maintain the number of workers in experimental cultures and prevent their dying out (Kipyatkov & Shenderova 1990). In fact, ail endogenous-heterodynamic species require not only diapause completion but exactly co Id reactivation, i.e. the winter exposure to low temperatures, to adequately restore their ability for productive brood-rearing (Kipyatkov 1994, 1996, Kipyatkov & Lopatina 2002c). The necessity of winter chilling for diapause completion in ants was tirst revealed by Delage (1968) for queen diapause in Messar capitatus and by Cagniant (1968) for larval diapause in Leptothora'{ monjan=ei. Then Passera (1969) discovered that when the workers of P. pygmaea kept without a queen al optimal temperature stopped laying after a long period of oviposition lhey could be provoked to renew egg-Iaying by keeping them al 10°C for no less than 15 days. Plateaux (1970, 1971) showed a 3-4 months exposure of L. nylanderi colonies to cold during autumn and winter to be crucial for the resumption of full development in spring. In sorne ants after a nuptial flight the inseminated Queens establish new nests at the end of summer but start egg-Iaying only in spring and need winter chilling for this (Benais 1972, Plateaux 1970). Final1y, the overwintering at cool temperature was shawn to be obligate for the production of alate sexuals, especially females, in numerous species oftemperate ants (Wesson 1940, Chauvin 1947, Brian 1955, Otto 1962, Passera 1969, Plateaux 1970, 1971, Buschinger 1973, Schmidt 1974, Cagniant 1988). Brian (1955) firstdemonstrated experimentally that overwintering at low temperatures was crucial for workers of Myrmica ruginodis to gain the ability to tenninate diapause in autumn larvae and for large diapause larvae to acguire the potency to develop into reproductive females. He called this process "vernalisation". In our experiments such an essential role of cold reactivatÎon was revealed for all endogenousheterodynamic species studied (Kipyatkov 1993, 1996, Kipyatkov & Lopatina 2002c). According to our data a period of 1-4 months (depending on species) of exposure to 3-5 oC is reguired for full reactivation. After such a treatment oviposition and development begin even at short days and 17-20°C, i.e. in circumstances that cause quick diapause onset in the same colonies in summer (see below). Thus, besides the completion of diapause, which may happen spontaneously or as a result of the influence oflong days, the apparent effects of cold reactivation. unachievable for temperate ants without winter eooling, include: (1) the restoration of the colony's "spring physiology" and full capability to realize a new brood-rearing cycle (nortnal queen fecundity, poteney of sorne larvae to develop into female reproductives, ability of workers to rear overwintered and rapid brood larvae without diapause and to produce alate sexuals), and (2) the changes of the nortn of reaction to photoperiod (generalloss of sensitivity in species that have photoperiodic responses sce below) and temperature (ability to produce eggs and rear larvae without diapause for a long period at rather low temperatures that induce diapause in summer). One could say that as a result of cold reactivation the ant colony's "sand-glass" tums over (Kipyatkov 1993, 1996). During the summer season the graduai decrease of a colony's capability to produce new eggs and to rear larvae without diapause and the increase of the bias for diapause occur as a result of the endogenous physiological and social processes, as though the sand in the ants' "sand-glass" po urs little by little out the upper reservoir to the lower one. AIso, the photoperiodic sensitivity of a colony appears and the reaction to temperature distinctly changes due to this process. As a result, in late summer lower temperatures and shorter days (only in sorne species) advance the onset of diapause, thus curtailing the period of oviposition and development. Such effects of external conditions were found in our experiments in aU species studied (Kipyatkov 1974a, 1977a, 1979, 1981, 1993,1996, Kipyatkov & Shenderova 1989, 1991, Kipyatkov & Lopatina 1990, 1993, 2002c, Lopatina & Kipyatkov 1993). Thus, the duration of a colony's annual cycle ofbrood-rearing in nature is controlled both by an endogenous timer (sand-glass device) and by exogenous environmental eues - temperature and photoperiod (in sorne species), whieh adjust the date of diapause onset to the climatic characteristics of a given year (Kipyatkov 1993, 1996, Kipyatkov & Lopatina 2002e). Temperature control of diapause is really univers al in ants. In ail species tested in our experiments higher temperatures delayed and lower temperatures advaneed the onset of diapause both in larvae and adults (Kipyatkov 1993, 1996, Kipyatkov & Lopatina 2002b,c). On the contrary, photoperiodic control of diapause is uncxpectcdly uncommon among ants. The photoperiodic responses in these insects were revealed for the first time in M rubra and M ruginodis (Kipyatkov 1972, 1974a). It has been shown that diapause arose sooner in larvae and queens the shorter was the day-Iength in the interval from 16 to 13 h characteristic for the study region in July-September (Kipyatkov 1974a, 1977a, 1979). When ant colonies in the autumn state were subjected to daylengths of 15 h, diapause ended both in queens and larvae (Kipyatkov 1977b ). Subsequently the existence of photoperiodic responses in M rubra was confirmed by Hand (1983) and Brian (1986). Nevertheless, the following extensive studies demonstrated that only sorne ants besides Myrmica used day-Iength as an environmental cue controlling oviposition, development and diapause onset. The diapause induetion was found to depend on photoperiods only in Aphaenogaster sinensis (Kipyatkov & Lopatina 1990) and Lepisiota semenovi (Kipyatkov & Lopatina 2002c). In addition in A. sinensis, Camponotus herculeanus, Leptothorax acervorum and }vfanica rubida we have observed higher incidence of diapause in larvae at short days compared with larvae in similar cultures at long days (Kipyatkov 1996). The genus Myrmica thus represents a rather curious exception amûng temperate ants since ail its species studied so farpossess clear-cut photoperiodic responses controlling the induction and termination of diapause (Kipyatkov 1972, 1974a, 1993, 1996, Kipyatkov & Lopatina, 1997b, 1999). Possible factors that prevent mû st ants from evolving photoperiodic control of diapause are discussed by Kipyatkov (1996). Thus, most temperate ant species rely upon internaI clocks as weil as on ambient temperatures in triggering the onset of diapause. In several endogenous-heterodynamic ants (most species belonging to genera Aphaenogaster, Crematogaster, Lasius, Mvrmica, Tapinoma) environmental cues ean alter the duration of the annual brood-rearing cycle within rather broad limits. For example, in Myrmica rubra and M. ruginodis short days and suboptimal temperatures of 17-20 oC in the middle of summer substantially advance the onset of diapause in larvae and queens (Kipyatkov 1 974a, 1 977a) while at long days and a temperature of25 oC, which is weIl above the optimum of these species (21-22 oC according to Brian 1973), egg-laying by queens and the development and pupation of rapid brood larvae continues for several months without a break (Kipyatkov 1979, Kipyatkov & Lopatina 1 997a). An example is given in Fig. 6. The seasonal cycle of oviposition and development in othcr species is controlled predominantly by the endogenous mechanisms, and the time of the onset of diapause depends only slightly on environmental conditions in these ants. Thus, temperature hardly modifies the intrinsic length of the queens' oviposition period in all studied species of the genus Formica (Kipyatkov & Shenderova 1989, 1991, Kipyatkov & Lopatina 1993). The annual brood-rearing cycle in species belonging to the genus Catag(vphis and the subgenera Camponotus s. str. and Leptothorax s. str. is also comparably independent of the environment (Kipyatkov 1993, 1996, Kipyatkov & Lopatina 2002c). FORMS AND PROPERTIES OF DlAPAUSE IN ENDOGENOUS-HETERODYNAMIC ANTS Larval diapause In most cases the diapause of larvae in ants is facultative, i.e. a given larva can either develop directly or enter diapause depending on the circumstances (Tab. 1). The diapause is induced by external factors and is normally ended due to diapause development at low temperatures (Kipyatkov 1993, 1996, Kipyatkov & Lopatina 2002c). In a few instances, however, the larval diapause can be obligate to some extent. Brian (1962, 1963) found that sorne Myrmica larvae emerging from the first eggs laid in spring had "a bias" for diapause and therefore they grew slowly, entered diapause and did not pupate without overwintering. Only at 24 cC and above could these larvae pupate if they were fed by workers with spring physiology (Brian 1963). Evidently, temperature can affect larval development and induce diapause both directly and through the nurse workers, although the latter route has been investigated so far in only one instance. Brian (1955) carried out experiments with separate chilling of diapause larvae and workers of M ruginodis and found that the process of vernalisation (see above) took place only in larvae, because larvae before overwintering ne ver developed into alate females even ifthey were fed by workers in a spring state, whereas larvae subjected to cold and reared by autumn workers sometimes became alates under the relatively high temperature of 25 oC. The ways by which the photoperiodic conditions can control larval diapause were studied in detai! in M rubra (Kipyatkov 1974b, 1976, 1981, 1988). Surprisingly, the larvae appearcd to be entirely in sensitive to the direct influence of photoperiods. Their development was instead controlled by workers who perceived the photoperiodic cues from the environment. Thus, non-diapause nurse workers (i.e. maintained under long days from the spring or activated by long-day photoperiods in autumn and, hence, physiologically active) stimulated rapid growth and pupation of summer larvae and tenninated diapause in autumn larvae, whereas diapause workers (i.e. subjected to 3-4 weeks influence of short days and, hence, physiologically inactive) were unable to maintain a high growth rate of larvae and instead induced diapause in them (Kipyatkov 1974b ). In fact, this was an example of social control of larval diapause by the workers. However, the first case ofsuch a control was described by Brian (1955) inM ruginodis. He found that the spring workers (i.e. ants immediately following prolonged overwintering in a refrigerator) stimulated fast growth and pupation of diapause autumn larvae both at 20 and 25 oC. However, similar diapause larvae did not develop at all when fed by autumn workers (i.e. ants which performed a complete cycle ofbrood-rearing at optimal temperature during three months after overwintering). The results of Brian were then confirmed by Weir's (1959) experiments on the same species; Weirrevealed also that young workers recently emerged l'rom pupae were similar in their influence on larvae to the autumn workers. Plateaux (1971) made analogous experiments on L. nylanderi and showed that spring workers of that species are able to terminate diapause of autumn larvae. In subsequent experiments Brian (1963) found one more highly interesting form of social control of larval diapause: the stimulating effect of a queen whose presence in a culture led to a 4-5-fold increase of the percentage ofpupating rapid brood larvae in comparison with ant cultures without queens. Afterwards, Kipyatkov (1979) repeated experiments of Brian (1955) on M rubra including naturalIy overwintered (spring) larvae as weil. Spring larvae did not pupatc at all under the cafe of diapause autumn workers, whereas naturally overwintered (spring) workers provoked growth and pupation in the majority ofboth spring and diapause autumn larvae. Significantly later we studied the phenomenon ofworker social control in seve rai ant species and made experiments according to the same exchange scheme with four combinations: (1) overwintered workers with overwintered larvae, (2) overwintered workers with diapause larvae, (3) diapause workers with overwintered larvae, (4) diapause workers with diapause larvae. The results ofthese experiments diflèred significantly among species (Kipyatkov & Lopatina 1994, 1999, Kipyatkov et al. 1996, 1997). In Camponotus herculeanus, C. japonicus and several Tetramorium species non-overwintered diapause larvae fed by spring workers developed rapidly and pupated within a short period whereas overwintered larvae p1aced into the nests with autumn workers did not develop and pupate at aIl or only a few of them pupated sometimes. Thus, the workers ofthese ants exercise full control over the development and the diapause oftheir larvae. However, in Leptothorax acervorum we found an entirely opposite situation: autumn workers cou Id not prcvent development of spring larvae and they ail pupated. At the same time overwintered workers stimulated development ofless than half of diapause larvae. In Afyrmica rubra, l'II. ruginodis, M. lohicornis and Lasius niger we observed an intermediate situation: only sorne spring larvae pupated when fed by autumn workers and also far from aIl autumn larvae fini shed development under the care of spring workers. Thus, the forms of social influence on diapause by workers are diverse in ants and range from nearly abso\ute control (in Camponotus and Tetramorium), wh en the physiological state ofworkers completely defines the fate oflarvae, to rather weak eftècts when diapause workers are unable to prevent the pupation of most overwintered larvae and spring workers are capable of inducing the development and pupation of only a few diapause autumn larvae (in Leptothorax). In most species (Lasius, Myrmica), however, the intermediate variants of diapause control are realized. There is some evidence that Myrmica workers can manipulate the development of larvae via changing the intensity of tactile stimulation and the frequency offeedings (Kipyatkov & Lopatina 1988, 1989a, b ). The stahility of larval diapause differs significantly among ant species. In sorne species the diapause is quite stable and cannot be broken by the influence ofhigh temperature and long days. Holldobler (1961) observed that C. herculeanus and C. ligniperda larvae did not grow and stayed in diapause for a long time under high temperature. The same appeared true for C. vagus (Renois 1972). Passera (1969) showed that autumn larvae of Plagiolepis pygmaea did not grow even at high temperature and could pupate only after normal overwintering. We also found such stable larval diapause in several species of Camponotus s. str. as weil as in Camponotus aethiops, P/agio/epis compressus and Tapinoma erraticum. The diapause larvae of ail such species do not take food and grow whiIe in diapause (Kipyatkov 1996, Kipyatkov & Lopatina 2002c). At the same time, in many endogenous-heterodynamic species larval dormancy is unsteady and they ail need lower temperature for diapause maintenance. Brian (1955) found that the diapause in autumn Myrmica larvae was rather unstable at 25 oC and many ofthem pupated in this situation. We observed such thermal termination of dia pause with the pupation of almost al! or of only part (depending on species) of diapause larvae in many endogenous-heterodynamic species belonging to the genera Aphaenogaster, Crematogaster, Lasius, Lepisiota, Leptothorax, Manica and Myrmica. Unlike the exogenous-heterodynamic species thermal termination oflarval diapause in endogenous-heterodynamic ants occurs only at temperatures weil above the optimum (Kipyatkov 1996, Kipyatkov & Lopatina 2002c). In man y ants, both endogenous- and exogenous-heterodynamic, which are characterised by diapause in the last larval instar, the diapause larvae continue to feed and to grow slowly and can attain a significantly larger size before overwintering. This trait was first recorded by Ezhikov (1929) in Leptothora.'<: but it was Brian (1955, 1968) who first understood its significance. He found that such diapause growth plays a peculiar role in the process of caste differentiation in ;tfyrmica. The diapause larvae grow in size but do not develop in tàct, since their imaginai buds remain the same size and do not differentiate. Only such large diapause larvae well grown in auturnn have the potential to develop into female reproductives in spring. Later, the sarne situation was discovered in L. nylanderi by Plateaux (1970). According to our data diapause growth is a property of species belonging to the generaDiplorhoptrum, Lasius, Leptothorax, Lepisiota, Manica, Messor, Alyrmica, Tetramorium, Camponotus (sorne species), Crematogaster and Monomorium (Kipyatkov 1996, Kipyatkov & Lopatina 2002c). Adult diapause The win ter dorrnancy is inevitable for ail adult inseets (except mos! winged reproductives) in a colony oftemperate ants since ail ofthem normally live for several years. Therefore, in the life cycle of each individual and of the colony as a whole the diapause arises and 1S completed repeatedly. Besides perennial social insects a recurrent reproductive diapause is known only in a few solitary species with diapause in the adult stage (Hodek 1979, 1983, 1998). The adult dia pause in endogenous-heterodynamic species is al ways ohligate in a sense that it en sues sooner or later under any circumstances (Tab. 1). Environmental cues, such as tempe rature and photoperiod (in some species), can only advance or delay the onset of diapause to sorne extent. In many ant species diapause in queens and workers is not stable and can easily be intelTUpted by the influence of aboye-optimum temperatures. These species are exactly the same as those listed above lhat have unstable larval diapause. ln ants having a photoperiodic influence on the induction of diapause, the diapause can easily be broken by exposure to long photoperiods. This socalled phofoperiodic termination of diapause is weil known in many insects, especially in species with diapause in the adult stage (Danilevskii 1961, Müller 1965, 1970, Hodek 1983, Danks 1987), and was found in our experiments in ail ii1yrmica specics studied (Kipyatkov 1972, 1977b, 1981, 1996, Kipyatkov & Lopatina 1997b, 1999) and in Aphaenogaster sinensis (Kipyatkov & Lopatina 1990). At the same bme, in some species the adult diapause is extrcmely stable and cannot be easily terminated by high temperatures and long days. Holldobler (1961) first observed such stable diapause in queens of C. hereuleanus and C. ligniperda kept at high temperatures. In experiments of Passera (1969) queens and workers of Plagiolepis pygmaea that had ceased 10 lay eggs at optimal temperatures did not start oviposition aga in without winter chilling. Wc found very stable queen diapause in the same species that had similarly stable larval diapause (listed above) and also in those species that pass winter without brood, i.e. in species of Formica and Catag(vphis, and also in Ponera coare/ata (Kipyatkov 1996, Kipyatkov & Lopatina 2002c). Adult ants, including workers and queens, while in the stale of diapause, retain the ability ta move freely and actively, ta collect food, to fced themselves and other individuals, i.e. ta behave as they usually do. The changes in behaviour conneetcd with diapause in adult ants might exist, but this problcm has not yet been studied except for one instance: diapause workers of !vfvrmiea ruhra are less aggressive and disposed to collect food in comparison with non-diapause ants (Kipyatkov 1976b ). During overwintering the diapause adults ofmost temperate ants are also able to move slowly at above zero temperatures. According to our observations, the cold coma temperatures in most northem ants during overwintcring are usually about or slightly below zero. When ants in a cold coma are wanned up they immediately resume normal activity. Ail this was first observed by Holmquist (1928) in Formica ulkei. At the same time, sorne ants fall into a state of complete stupor, even deep lethargy, during overwintering, and they need a rather long period at warm conditions ta awake complctely from this cataleptic state. Holmquist (1928) first described this phenomenon in Camponotus pennsylvanicus workers. We observed the same lethargie dormancy only in C. herculeanus, C. ligniperda Harpagoxenus sublaevis and Leptothorax acervorum. Diapause of adults in insects is primarily reproductive diapause and is characterized by an inactive state of the reproductive system and by the inability offemales to lay eggs (Danks 1987). This statement is also correct for ant Queens and workers. Diapause Queens do not lay eggs and their ovaries contain no eggs and developing oocytes during this period (Kipyatkov & Shenderova 1990, Kipyatkov 1996, Kipyatkov & Lopatina 2002c). Workers in most ants are also able to lay eggs, either fertile haploid eggs developing into males (when the queen is absent in a colony), or infertile trophic eggs (in the presence of a queen) to be used as food for larvae and Queens (Hôlldobler & Wilson 1990). Following overwintering the workers in cultures without Queens normally lay fertile eggs during sorne period but then stop oviposition and stay in that diapause state for a long time. This was shown in Myrmica ruginodis (Brian 1953), Plagiolepis pygmaea (Passera 1969), Leptotharax nylanderi (Plateaux 1970), Cataglyphis cursar (Cagniant 1979, 1980) and in our experiments in Lasius niger, L. jlavus, L. acervorum, Tapinoma karavaievi and several species of Formica (Kipyatkov 1996, Kipyatkov & Lopatina 2002c). KneÏ1z (1970) described the seasonal cycle in the state ofworker ovaries in Formica po/yctena and found that the percentage of workers with well-developed ovaries attained a maximum in July, but by October the ovaries in ail workers became completely undeveloped, which is a good indication of diapause onset. After an exposure to short days the workers of M rubra in cultures without Queens did not lay eggs whereas they still produced eggs under long days (Kipyatkov 1976b ). Ambient temperature evidently affects ail adult ants in a colony directly. We know nothing about possible indirect effects oftemperature eues. However, photoperiodic eues act both directly and indireetly, i.e. by means of sorne mediators. Evidently, forager ants exiting from the nest for food are able to perceive photoperiodic cues directly, but they do not feed larvae themselves. How can the Queens and nurse workers which normally never leave the nest perceive photoperiods? Could the photoperiodic response be realized ifthere were constant darkness inside the nest? In order to test this situation a speciallaboratory formicarium with a completely light-insulated ne st ch am ber was constructed, where only workers were allowed to get out to the illuminated section but Queens were prevented l'rom doing so by a wire mesh at the exit hole. A quite normal photoperiodic response both during induction and termination of diapause was obtained in colonies of M nJbra kept in such fonnicaria (Kipyatkov 1976b ). This means that if only sorne workers regularly leave completely dark nests it is sufficient for the effective photoperiodic control of diapause both in larvae and queens. We then tested whether workers could control diapause in Queens the same way as they govern the development of larvae (see above). It was found that M rubra Queens were able to respond to photoperiodic cues themselves but the workers also very strongly affected their Queens: non-diapause workers quickly terminated diapause in Queens kept under short days but diapause workers only succeeded in decreasing the number of eggs laid by Queens under long photoperiods (Kipyatkov 1976b ). The physiological state of the queens is, thus, only under partial control of the workers in this species. This fonn of social control of diapause was later investigated in sorne other ant species lacking photoperiodic responses. We used the same four combinations as in experiments wÎth larvae (see above): (1) overwintered workers with overwintered queen(s), (2) overwintered workers with diapause queen(s), (3) diapause workers with overwintered queen(s), (4) diapause workers with diapause queen(s). In tluee Formica species the induction and termination of queen diapause proved to be completely free from worker influence, whereas in other ants (Lasius niger, Tetramorium) it was under partial control ofworkers, similar to Myrmica: spring workers were able to interrupt the diapause in queens but autumn workers eould not prevent egg-Iaying by overwintered queens (Kipyatkov 1996). An entirely new form of social control was also found in L. acervorum: spring larvae by unknown means affected queens and workers and terminated their diapause; as a re!'mlt the workers activated by these larvae were able ta provide adequate care and feeding not only for overwintered larvae but also for those larvae that originated from eggs laid by queens that had emerged from diapause; this response led to the unusual appearance of rapid-brood pupae in ant colonies without overwintering (Kipyatkov et al. 1997). How do the forager workers in M rubra colonies manage to transmit the information on photoperiodic cues from the outside of the nest to queens and nurse workers? Probably they use chemical mediators for this purpose. The existence of one sueh ehemieal signal was shown by Kipyatkov 1988, 2001). This substance was called activator pheromone sinee it terminated diapause in larvae and queens, i.e. exerted an activating eiTeet on them. Unfortunately, no further experiments have been carried out in this very promising direction. In particular, we still do not know ifthere exists also an inhibitor pheromone causing the onset of diapause in larvae and queens. source -------------------- |
|
|
Monday 07 December 2009 à 14:45
Message
#7
|
|
Myrmécomorphe Groupe: Contributeurs Messages: 5 633 Inscrit: 20/08/2007 Lieu : Armentières (59) Membre No.: 1 645 |
Un ou plusieurs volontaires pour une belle traduction serait effectivement pas mal, même si hugo a résumé l'essentiel
Ce deuxième document est un peu technique et assez long, mais accessible et très clair je trouve Il y a pleins d'informations sur les différentes stratégies pour faire face à cette période de froid et la nécessité ou non de cette diapause, pour quelques genres et espèces de nos régions. -------------------- |
|
|
Version bas débit |