Abstract: This paper deals with an important aspect of adaptation to the northern environment, the temporal synchronization of populations with seasons, i.e., phenology of Drosophila species. Winter dormancy is the main synchronizer in northern areas. Extensive reviews of this subject do not contain any information on Drosophila (e.g., Lees, 1955; Danilevskii, 1965; Beck, 1968; Danilevsky et al., 1970).

Abstract: Photoperiodic responses of insects and mites have been studied by physiologists, biochemists, ecologists, morphologists, geneticifets, and evolutionary biologists. Data obtained using the methodologies of each of these disciplines has led to an understanding of parts of the “diapause phenomenon.” This symposium has stressed the evolutionary and ecological aspects of diapause and migration as a means of escape in space and time. This chapter will stress some of the practical implications of the observed intra- and interpopulation variability in diapause responses in insects and mites.

Abstract: The larvae of the spotted stalk borer Chilo partellus and the coastal stalk borer Chilo orichalcociliella enter aestivation-diapause in the stalks of maize stems soon after the rains have ceased. In the field prediapause larvae were found in maize plants of different developmental stages, ranging from early vegetative to beyond maturity: the growth stage is not responsible for the induction of aestivation-diapause. The first symptoms of the diapause syndrome appear in larvae feeding in stems containing relatively high water contents and low protein contents. Diapause could be “artificially” induced in non-diapause larvae introduced into aged maize stems. Larvae beyond the fifth instar had developed too far to be sensitive to the factors in these stems which trigger diapause. The larval pigmentation as a criterion for aestivation-diapause is discussed. RESUME LA CONDITION DE LA PLANTE-HOTE PENDANT LA DIAPAUSE D'ESTIVATION DES PYRALES CHILO PARTELLUS ET CHILO ORICHALCOCILELLA AU KENYA Les larves des pyrales Chilo partellus et Chilo orichalcocilella commencent la diapause d'estivation dans les tiges de mais peu apres la cessation des pluies. Des larves a l‘etat de pre-diapause ont ete t'rouvees sur les lieux dans des plantes de mais a differents stades de developpement, s’eehelonnant du premier stade vegetatif a passe maturite: la phase de croissance n'est pas responsable de l'induction de la diapause d'estivation. Les premiers symptomes du syndrome de diapause apparaissent dans les larves se nourrissant de tiges ayant une teneur en eau relativement elevee et une teneur en proteines faible. La diapause pourrait etre provoquee “artificiellement” dans les larves n‘etant pas en etat de diapause introduites dans des tiges de mais âgees. Au-dela du cinquieme instar, les larves etaient trop developpees pour etre sensibles aux facteurs declanchant la diapause presents dans ces tiges. La pigmentation larvaire comme critere pour la diapause d'estivation est discutee.

Abstract: The hormonal control of implantation in mammalian species with and without embryonic diapause is described. In a majority of species displaying the obligate form of diapause the corpora lutea appear to exhibit a low level of steroidogenic activity throughout diapause, full luteal activity being resumed just before the initiation of implantation. Fluctuations in the plasma levels of oestrogen and progesterone during diapause may serve to prime the uterus for implantation. In species exhibiting the facultative form of diapause, such as the rat and mouse, both progesterone and nidatory oestrogen are required for the induction of implantation. In species not displaying embryonic diapause implantation will take place in the presence of progesterone alone. In the light of these considerations the selection of animal models for drug-screening purposes and possible new approaches to contraception are discussed.

Abstract: Nothobranchius guentheri is an East African annual fish found in temporary bodies of water in areas of alternating rainy and dry seasons. During the dry season the embryos may be exposed to temperature extremes. Embryos have been reported to undergo diapause (developmental arrest), and are thus able to withstand the variable durations of the dry seasons. Since the embryos appear to endure long durations in diapause, and since in diapause they may be exposed to large variations in temperature, we have attempted to determine the thermal tolerance and responsiveness of embryos at diapause and at stages exclusive of diapause. Embryos were exposed to temperatures ranging from −8-40°C for variable durations of time, and survival, abnormalities and developmental rates determined. Both Diapause I and Diapause II embryos were much less sensitive to temperature extremes than were the other stages, and Diapause II was much less sensitive than Diapause I. Abnormalities only occurred under certain temperature exposures but showed the highest frequency at the early stages of development. Short exposure of Diapause I embryos to −8 and 3.4°C eliminated Diapause II, while short exposure to 40°C enhanced its duration. Although it has been proposed that the onset and duration of the diapauses are denendent on the oxygen concentration of the water, we propose that temper ature may also be another imposrant factor.

Abstract: Aedes sierrensis (Ludlow) (Diptera: Culicidae) relies upon photoperiod to initiate a 4th instar diapause at 16.5°C. Short days elicited 100% diapause among larvae from central Oregon and northern California, but thereafter the incidence of diapause declines with latitude so that in southern California only 35% of the sample populations entered diapause. Among that portion of the population capable of responding to day length, the critical photoperiod increased by one h for each 4.8° increase in latitude of origin.

Abstract: Stalk borers are highly destructive to a large number of important graminaceous crops all over the world. Some examples of economically important stalk borers and a general description of their life-cycle are mentioned in chapter 1. In the same chapter difficulties in controlling the insects are described. The crucial role of aestivation- diapause in the life history of tropical stalk borers is elucidated and the importance of further research on this subject is demonstrated. Aestivation-diapause in two Pyralid stalk borers, Chilopartellus (Swinhoe) and Chilo orichalcociliella (Strand) was investigated under field and laboratory conditions. The relation between diapause and climate during three consecutive years is described in chapter 2. Yearly and seasonal fluctuations in the larval and pupal populations of the two stalk borers in maize appeared to be considerable. As long as the water conditions for plant growth were suitable, insects had a continuous development. Under these conditions larvae had pigmented spots and could not survive dry conditions. Soon after cessation of the rains (or irrigation) rates of pupation decreased. At that time larvae lost their cuticular pigmentation and became resistant to drought. Comparison of the incidence of aestivation in the field with the prevailing climatic conditions showed that only lack of rain could be associated with the arrested larval development. No effects of temperature, relative humidity or photoperiod could be found. These results indicate that the host plant may be involved in the induction of diapause. Chapter 3 is concerned with characteristics of pre-diapause and diapause larvae. Evidence was obtained that under natural conditions larvae do not feed during diapause as long as they are not disturbed. The physiological condition of field-collected stem borer larvae changed considerably upon entering diapause: a decreased rate of oxygen consumption, rate of heart beat and water content, an increased fat content, and arrested development of the testes were found. These changes normally occurred before larvae were turning unspotted and/or were becoming resistant to drought. The condition of the host plant in relation to diapause induction is described in chapter 4. Diapause could be induced inside maize plants of different developmental stages. It was shown that the first (physiological) signs of the diapause syndrome appear in larvae feeding in stems containing 70-80% water and very little ( Marked differences were found in the consumption and utilization of stems of maize plants in different developmental stages. Its possible relevance to diapause is discussed. In chapter 5 experiments are described on the induction of aestivation-diapause by varying the food condition. Most early 5th instar larvae of C. partellus entered diapause after being introduced into aged maize stems containing 75% water, 8% sugar and 1.3% protein (fresh wt.). Pupation rate, cuticular pigmentation, QO 2 and water content of these larvae were comparable to values obtained from field-collected aestivating larvae. Larvae which had developed beyond the early 5th instar were less sensitive to the diapause inducing factors of the aged maize stem : most of them pupated. Test of 30 different diets with varying protein, sugar and water contents, indicated that diets containing 0.9-1.1% protein and 70% water were best in inducing diapause. Early 5th instar larvae on diets with the above mentioned protein content grew slowly (but reached normal weights), moulted into the unspotted form and had a retarded rate of pupation. Larvae on diets with lower protein contents hardly developed at all, whereas on diets with higher protein contents larvae pupated normally. Larvae reared on diets in which the water content had been reduced from the normal level of 86% to 70%, resulted in a reduction of the larval water content and respiratory rate, close to values normal for field-collected diapause larvae. Evidence was obtained that larvae reared on diapause inducing diets attained a certain degree of drought resistance. Early 5th instar or younger larvae were the most sensitive stages to diapause induction by diet. Many larvae on aged maize stems and artificial diets turned unspotted even though pupating soon thereafter. The relevance of the cuticular pigmentation as a criterion for aestivation-diapause is discussed. The endocrine involvement in the aestivation- diapause is described in chapter 6. From juvenile hormone titre determinations and ligation experiments evidence was obtained that the diapause is regulated by an intermediate level of JH. Application of JH to non-diapause larvae prevented pupation of these larvae but did not evoke other aspects of the diapause syndrome.

Abstract: . During maturation of adult female Leptinotarsa decemlineata, synthesis of specific proteins by the fat body was investigated with the aid of in vitro incubations. Both vitellogenins and diapause proteins were present in all females. Under long days high rates of vitellogenin synthesis were observed, which were not reflected in the amount of vitellogenin present in the haemolymph. Under short days synthesis of three diapause proteins predominated. The highest rates of synthesis of these proteins occurred during the second half of the prediapause period. At the same time storage of two diapause proteins by the fat body was observed. Comparison of the synthesis of specific proteins in vivo and in vitro revealed the fat body as the main producer of haemolymph proteins.

Abstract: Few insect species encounter environmental conditions which remain favourable for continuous growth, development, and reproduction throughout the year. Such species are said to be homodynamic: they have life cycles characterised by a lack of seasonally synchronised adaptations. Most species however, inhabit regions in which seasonal variations in environmental conditions impose a corresponding seasonal change in rate of development, altc.rnating between periods of rapid growth and reproduction, and a period of rest or dormancy. Such heterodynamic life cycles are typical of temperate latitudes where seasonal adversities, such as low temperatures often combined nith the absence of food, retard or completely inhibit development during winter. However, even in tropical latitudes, the alternation of a wet ~vith a dry season can also result in specific life cycle adaptations linked temporally to these environmental chaqes. This paper is concerned with those strategies found in insecmt life cycles which enable them to survive unfavourable, recurrent changes in their environment. In general, these comprise 2 basic strategies: a migration, and b dormancy. Migration is well documented for Northern Hemisphere insects. It may consist simply of flight from emergence site to another place, \\.here gro~vth and reproduction can continue; or it may be combined with a dormancy state such as adult (reproductive) diapause. .An example of the latter in North ,4merica is the monarch butterfly, Danaus plexippus (L.) which migrates and then enters an overwintering adult diapause (Urquhart 1976) ; and in Australia, the bogong moth, Agrotis infusa (Boisd.) which migrates and then enters an aestival (summer) adult diapause (Common 1954). The second major seasonal strategy, that of dormancy, includes the following resting conditions. A Summer dormancies

Abstract: Snow depth is the most important environmental factor in the survival of overwintering Rheumaptera hastata (L.) pupae in interior Alaska. Pupae spend the winter in the leaf litter where litter temperatures are directly related to snow depth at given air temperatures. Winter survival is also dependent on the cessation of pupal development (diapause) and the development of cold-hardiness which is induced by certain physiological processes such as supercooling and changes in glycerol and carbohydrate levels. Glycerol content and supercooling are dependent on changes in carbohydrate levels which in turn are directly related to changes in the rate of pupal development prior to diapause.

Abstract: Numbers of late-instar larvae, pupae, and adults of Heliothis zea (Boddie) produced from ears of late-planted corn were estimated. Larval and pupal production ranged from 1.3–2.5/ear and from 0.6–0.8/ear, respectively. Survival of individuals from late–instar larvae to pupae ranged from 33.0–55.3%. Of those surviving, 21–84% were in diapause. Survival of diapausing pupae from fall to spring was 7.7–58.8% and of the fall pupal population to emerged adults, 1.9–27.9 %. Of the total larvae produced in the late-planted corn with the potential for developing to diapausing pupae, only 0.7–9.2% produced spring adults. Cannibalism was considered an important mortality factor limiting the production of late-instar larvae. Heavy mortality occurred from spring diapause termination to adult emergence. A technique found useful in monitoring pupal production from corn ears is described.

Abstract: Microplitis plutellae, one of the principal parasites of the larvae of the diamondback moth Plutella xylostella, has a diapause in a portion of each of its several annual generations, occurring in the cocooned pupae or prepupae. In experiments, development resumed and adults emerged from most insect material in diapause after exposure to 0 °C for a period equal to the duration of a Saskatchewan winter, about 160 days. Of diapausing insects that did not respond to such a period of cold treatment, some did so after subjection to a further period of low temperatures of a similar duration. Diapausing M. plutellae were shown to tolerate sub-freezing temperatures in the laboratory and to survive Saskatchewan winter temperatures under snow cover in the field. There is no evidence that the other major parasite of diamondback larvae, Diadegma insularis, enters diapause or winters in Saskatchewan.

Abstract: (1978). Variations in voltinism and diapause intensity in Nemobius sylvestris (Bosc.) (Orthoptera: Gryllidae) Journal of Natural History: Vol. 12, No. 4, pp. 461-472.

Abstract: Diapause induction studies showed that face flies, Musca autumnalis De Geer, from a recently established colony, entered diapause more readily than those that had been colonized for many years. Photoperiods of less than 16 h of light induced diapause at 16° and 27 °C but more flies entered diapause at 16°C. Maximum numbers of flies entered diapause under total darkness at 16°C, but the critical photoperiod corresponding to natural periods of daylight in late summer was 15 h of light at 16°C. Diapause termination studies indicated that 4 months’ exposure to 5 °C under total darkness was required for the termination of diapause.

Abstract: The features of larval diapause differ according to the species. In females undergoing imaginal diapause, the state of immaturity varies from one species to another.

Abstract: Twelve species of Limnephilidae were found as larvae in temporary stillwater habitats in Scotland and England. Studies on the life-histories of six of these demonstrated several adaptations associated with colonisation of such habitats. Adults had an ovarian diapause and laid eggs out of water in places where water stood the previous winter. Larvae could remain dormant within the egg-mass for at least 18 weeks, and did not escape until immersed in water. Control experiments suggested that species inhabiting permanent waters do not show these adaptations.

Abstract: The elaborate behavior of pre-diapausing larvae of the southwestern corn borer, Diatraea grandiosella Dyar, and the probable involvement of juvenile hormone (JH) in its control is described. At the end of their feeding period, pre-diapausing larvae descend to the root zone, excavate a cell in the stalk crown, prepare a plugged exit hole for the emergence of the adult, and molt from a spotted to an immaculate morph. They may also girdle the host plant just above ground level. In contrast to last stage non-diapausing larvae, last stage pre-diapausing larvae were found to retain a high JH titer in their hemolymph. The Galleria wax test showed that at the time pre-diapause behavior is initiated the hemolymph contains a mean JH titer of about 2600 Galleria Units/ml, and retains a mean JH titer of > 1230 GU/ml throughout the immediate pre-diapause period. In addition, the treatment of non-diapausing larvae with JH mimic induced some of the behavioral traits shown by pre-diapausing larvae. These findings suggest that JH potentiates the pre-diapause behavior. Prediapause behavior appears to be regulated by environmental cues (short days, low temperatures, senescence of host plant) linked to diapause determination, and operating through the neuroendocrine system.

Abstract: Duration of the feeding stage and corresponding weight increase during the last larval instar of the codling moth,Laspeyresia pomonella, are controlled by JH. Larvae reared under short day conditions have a relatively high titer of JH during the last larval instar and enter diapause as mature larvae. They feed longer and become heavier than larvae reared under long day conditions, which have no JH during the last larval instar and pupate when mature. By application of the JH mimetic Altosid® during the first 2 or 3 days of the last larval instar, the duration of feeding activity of larvae reared under respectively long and short day conditions was prolongated and the larvae became significantly heavier. The feeding behaviour could only be influenced by the juvenoid as long as the feeding activity of the larvae had not yet ceased.

Abstract: Facultative pupal insect diapause is induced by daylight rhythm and temperature furnished for the larval growth. Receptors of these factors are generally considered as larval eyes or brain. This work analyzes the possible role of pterobilin pigment of hemolymph and integument. This pigment seems to act independently and, sometimes with antagonistic actions, on the general physiology.