Adult Diapause Research Articles

Suppression of water loss during adult diapause in the northern house mosquito,Culex pipiens

One of the major challenges of overwintering in the mosquito, Culex pipiens, is prevention of dehydration. In this study, we compare the water balance requirements of nondiapausing and diapausing adult females of C. pipiens. Although their percentage water content is lower, diapausing females contain both higher initial and dry masses than nondiapausing individuals. Both nondiapausing and diapausing females tolerate a loss of up to 40% of their water mass before dying, but diapausing female C. pipiens reach this point after a longer period due to their lower rate of water loss. Males, which do not overwinter in diapause, showed no differences in their water balance characteristics when reared under diapausing or nondiapausing conditions. Likewise, no changes were noted in the water balance of pupae, indicating that diapause-related changes do not occur prior to adult eclosion. This mosquito does not replenish internal water stores by generating metabolic water or by absorbing vapor from the atmosphere, but instead relies on drinking liquid water (or blood feeding in the case of nondiapausing females). The critical transition temperature, a point where water loss increases rapidly with temperature, was the highest for females, then males, then pupae, but was not influenced by the diapause program. Females in diapause did not utilize common polyols (glycerol, trehalose and sorbitol) to retain water, but instead the presence of twice the amount of cuticular hydrocarbons in diapausing compared with nondiapausing females suggests that the deposition of hydrocarbons contribute to the reduced rates of water loss. The laboratory results were also verified in field-collected specimens: mosquitoes in the late fall and winter had a lower percentage water content and water loss rate, higher initial mass, dry mass and more cuticular hydrocarbons than individuals collected during the summer. Thus, the major features of diapause that contribute to the suppression of water loss are the large size of diapausing females (reduction of surface area to volume ratio lowers cuticular water loss), their low metabolic rate and the deposition of extra cuticular hydrocarbons.

Boll Weevil (Coleoptera: Curculionidae) Adult Diapause Responses to Selected Environmental and Dietary Conditions

Diapause in the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), remains a contentious issue despite intense investigation. In particular, the roles and interactions of photoperiod, temperature, and adult diet are poorly understood. We reexamined the influences of these factors by using a feeding regime typical of previous studies (group, one square per five weevils per day) as well as one known to promote reproductive development (single, one square per weevil per day). Three separate studies each incorporated all combinations of the following: photoperiod (short day, 11:13; long day 13:11 [L:D] h), temperature regime (constant 29.4°C; warm day, cool night, 29.4°C:10°C [day:night]), feeding regime, and age at dissection (3, 6, 9, and 12 d after adult eclosion). Studies differed in the source of weevils (Lower Rio Grande Valley, Brazos Valley of Texas), and the photoperiod used to rear weevils to adulthood (11:13 or 13:11 [L:D] h). Interpretable effects of photoperiod on diapause induction were not observed. Cool nights delayed development of fat bodies, oocytes with yolk, and the occurrence of diapause, especially in weevils fed in groups. However, these effects were not apparent by day 12. The most marked responses were to feeding regime. Hypertrophied fat bodies and diapause generally occurred more often, and oocytes with yolk less often, for weevils fed in groups compared with those fed singly. Fundamental differences in diapause response corresponding to rearing conditions or source of weevils were not observed. These results suggest improved understanding of the dynamics of adult diapause could be achieved through continued investigation of the effects of adult diets.

Photoperiodic control of diapause termination, colour change and postdiapause reproduction in the southern green stink bug, Nezara viridula

Abstract The effects of day length on adult diapause development, associated with diapause body colour change as well as postdiapause reproduction are studied in Nezara viridula from Japan. Facultative diapause spontaneously terminates under three constant short‐day and near‐critical photoperiods at 25 °C without low temperature treatment. The period required for body colour change from russet to green and the precopulation and preoviposition periods differ significantly between the photoperiodic treatments, being shortest under LD 13 : 11 h, intermediate under LD 12 : 12 h and longest under LD 10 : 14 h. Photoperiodic conditions do not affect postdiapause reproductive performance: the total egg production, duration of the period of oviposition and other reproductive indices do not differ significantly between the photoperiodic conditions. The total egg production depends on the duration of the period of oviposition but not on how long females remained russet during diapause. It is concluded that diapause in N. viridula does not require low temperature for its successful completion and diapause duration affects winter survival but not postdiapause reproductive performance or longevity. Such independence of the postdiapause reproductive performance from the duration of diapause may have contributed to the continuous worldwide range expansion of this species into temperate zone.

Upregulation of two actin genes and redistribution of actin during diapause and cold stress in the northern house mosquito, Culex pipiens

Two actin genes cloned from Culex pipiens L. are upregulated during adult diapause. Though actins 1 and 2 were expressed throughout diapause, both genes were most highly expressed early in diapause. These changes in gene expression were accompanied by a conspicuous redistribution of polymerized actin that was most pronounced in the midguts of diapausing mosquitoes that were exposed to low temperature. In nondiapausing mosquitoes reared at 25 °C and in diapausing mosquitoes reared at 18 °C, polymerized actin was clustered at high concentrations at the intersections of the muscle fibers that form the midgut musculature. When adults 7–10 days post-eclosion were exposed to low temperature (−5 °C for 12 h), the polymerized actin was evenly distributed along the muscle fibers in both nondiapausing and diapausing mosquitoes. Exposure of older adults (1 month post-eclosion) to low temperature (−5 °C for 12 h) elicited an even greater distribution of polymerized actin, an effect that was especially pronounced in diapausing mosquitoes. These changes in gene expression and actin distribution suggest a role for actins in enhancing survival of diapausing adults during the low temperatures of winter by fortification of the cytoskeleton.

Independence of Genetic Geographical Variation between Photoperiodic Diapause, Circadian Eclosion Rhythm, and Thr-Gly Repeat Region of the Period Gene inDrosophila littoralis

Drosophila littoralis is a latitudinally widespread European species of the Drosophila virilis group. The species has ample genetic variation in photoperiodism (adult diapause) and circadian rhythmicity (pupal eclosion rhythm), with adaptive latitudinal clines in both of them. The possible common genetic basis between the variability of photoperiodism and circadian rhythms was studied by a long-term crossing experiment. A northern strain (65 degrees N) having long critical day length (CDL = 19.9 h) for diapause, early phase of the entrained rhythm in LD 3:21 (psi(LD3:21) = 12.3 h), and short period (tau= 18.8 h) of the free-running rhythm for the eclosion rhythm was crossed with a southern strain (42 degrees N) having short CDL (12.4 h), late eclosion phase (psi(LD3:21) = 20.2 h), and long period (tau= 22.8 h). After 54 generations, including free recombination, artificial selection, and genetic drift, a novel strain resulted, having even more "southern" diapause and more "northern" eclosion rhythm characteristics than found in any of the geographical strains. The observed complete separation of eclosion rhythm characteristics from photoperiodism is a new finding in D. littoralis; in earlier studies followed for 16 generations, the changes had been mostly parallel. Evidently, the genes controlling the variability of the eclosion rhythm and photoperiodism in D. littoralis are different but closely linked. To test for the possible gene loci underlying the observed geographical variability, the period gene was studied in 10 strains covering all the known clock variability in D. littoralis. The authors sequenced the most suspected Thr-Gly region, which is known to take part in the adaptive clock variability in Drosophila melanogaster. No coding differences were found in the strains, showing that this region is not included in the adaptive clock variability in D. littoralis.

Effects of photoperiod and temperature on the induction of adult diapause in Dolycoris baccarum (L.) (Heteroptera: Pentatomidae) from Osaka and Hokkaido, Japan

Effects of photoperiod and temperature on the induction of adult diapause were examined in Dolycoris baccarum (L.) collected in Osaka and Hokkaido, Japan. Adults started reproduction soon after adult emergence under long-day conditions, while they entered diapause under short-day conditions. The critical photoperiod for the induction of diapause was between 13 and 14 h and between 15 and 16 h in insects of the Osaka and Hokkaido populations, respectively. Under long-day conditions, most insects of the Osaka population emerged as reproductive adults at any temperature used, whereas those in the Hokkaido population tended to show lower incidence of diapause as the temperature increased. Preoviposition periods in females of the Osaka population were shorter than those of the Hokkaido population. The duration of diapause in the Osaka population was shorter at 30°C than at 25°C under short-day conditions. In Osaka, D. baccarum is assumed to produce three generations a year, like several other seed-sucking bugs. In Hokkaido, a greater proportion of adults produces the second generation in summer under long daylengths.

Photoperiodic induction and termination of summer diapause in adult Epilachna admirabilis (Coleoptera: Coccinellidae) from a warm temperate region

In warm temperate and subtropical regions an adult summer diapause regulates the timing of oviposition. Epilachna admirabilis is a univoltine phytophagous lady beetle ranging from south to north Japan, Taiwan, China and Myanmar. In Japan the species hibernates in the full-grown larval stage. In cool temperate Sapporo (43°04´N) the adults never enter summer diapause but pass a second winter in diapause. This study revealed that in Kyoto (35°01´N), the adults had a summer diapause induced by an intermediate photoperiodic response; they had a critical photoperiod of approximately 14.5 h light per day. All females entered reproductive diapause under a long photoperiod of 16L (light) : 8D (dark) and 6.7% of them did so under shorter photoperiods of 13L : 11D and 12L : 12D. However, diapause incidence was 40% at 8L : 16D, suggesting the existence of a second critical photope- riod at a photophase slightly less than 8 h. At photophases of 12-15 h, non-diapausing females laid eggs on average between 27.1 to 39.0 days after emergence. Photoperiod reversibly regulated the induction, maintenance and termination of the adult diapause. Tem- peratures of 20-30°C did not affect the incidence and termination of diapause at 16L : 8D. Adult winter diapause at the higher lati- tude Sapporo might have originated from adult summer diapause at middle latitude regions such as Kyoto. Selection at increasing latitudes would have forced northerly populations of the species to lose the adult summer diapause in the range of natural day- lengths. Subsequent selection pressure should have favored adults that avoided futile oviposition in late summer or autumn, survived cold winters in diapause and commenced an additional oviposition in the second summer. Thus, a latitudinal difference in photoperi- odic responses might have developed.

Overwintering Strategies Depending on High Cold Hardiness in Nondiapause Stages inBruchidius dorsalis(Coleoptera: Bruchidae)

Bruchidius dorsalis Fahraeus (Coleoptera: Bruchidae) enters winter diapause in either the fourth (final) instar or during the adult stage (Kurota and Shimada 2001, 2003b). In the middle part of Japan, it overwinters in several developmental stages: nondiapausing young instars, diapausing instars, and adults (Kurota and Shimada 2002). To understand the relationship between the complex overwintering stages and the adaptive diapause strategy of B. dorsalis, I investigated (1) overwintering survivorship in developmental stages observed in the field and (2) cold hardiness at all stages including nonoverwintering ones such as eggs and pupae after enduring a controlled chilling experiment at 5°C for 100 d. The following results were obtained: (1) survivorship of nondiapausing larvae under natural conditions was almost as high as that of diapausing larvae and adults, and (2) cold hardiness in eggs and pupae was much lower than the other developmental stages in terms of survivorship and reproductive ability after the chilling treatment. From these results, I concluded that larval and adult diapause of this species would be induced at the most appropriate time to avoid overwintering in developmental stages with low cold hardiness. The complex overwintering stages in species that inhabit the middle part of Japan are likely to result from the adaptive timing of diapause induction at the two stages.

PHOTOPERIODIC CONTROL OF ADULT DIAPAUSE IN CHRYSOPERLA SINICA (TJEDER) (NEUROPTERA: CHRYSOPIDAE— I. CRITICAL PHOTOPERIOD AND SENSITIVE STAGES OF ADULT DIAPAUSE INDUCTION

Abstract Photoperiodic sensitivity for diapause induction of the green lacewing, Chrysoperla sinica (Tjeder) was examined at 22°C. The adult diapause of C. sinica was induced by short‐day photoperiods, and the critical photoperiod for its induction was between 12.5L‐11.5D and 13L‐11D.Adults developed without diapause under long‐day conditions, and entered diapause under short‐day conditions. The adult stage was the uppermost sensitive stage for adult diapause induction, adults could go into diapause only when the emerging adults were under diapause‐inducing short‐day photoperiods. The short‐day photoperiodic experience by transferring between 15L: 9D and 9L: 15D at preimaginal stages did not result in adult diapause under 15L: 9D photo regime, although some treatments extended the pre‐oviposition period in adult stage. The results showed that the 3rd instar larvae and pre‐pupae were more sensitive to the photoperiodic change from 15L: 9D to 9L: 15D photo regime than the other preimaginal stages.

Diapause in the calanoid freshwater copepod Eudiaptomus graciloides

The seasonal appearance and the intensity of diapausing-egg production in Eudiaptomus graciloides in five lakes of different size and trophic level were studied. In all lakes, diapausing eggs were produced in autumn. In the large mesotrophic lake Selenter See, the population’s shift to the production of diapausing eggswas morecompletethan in other lakes.Weexamined daylength, temperatureand foodasproximate factors for the production of diapausing eggs with laboratory experiments. Eudiaptomus graciloides produced diapausing eggs in all treatments, but a significantly higher percentage of diapausing eggs was found under short day conditions except when algal food was abundant and temperature was high. To investigate the adaptive significance of diapause in E. graciloides, we compared the survival of adult and juvenile at different temperatures for E. graciloides with Eudiaptomus gracilis, a sympatric species that does not exhibit diapause. At 8 � C, adult E. graciloides survived better than adult E. gracilis and exhibited reduced gut contents and accumulation of storage lipids, traits characteristic of adult diapause. Eudiaptomus graciloides nauplii did not reach the copepodid stage at 6 � C, but E. gracilis nauplii exhibited high mortality and developed very slowly. We hypothesize that adult diapause and production of diapausing eggs facilitate the survival of E. graciloides during cold periods and enhance coexistence with its congener, E. gracilis, in temperate zones.

Environmental regulation of the purine synthesis enzyme purH transcript during adult diapause in Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

A 1962 bp cDNA clone of 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase (purH) was isolated from diapausing adults of Leptinotarsa decemlineata using RT-PCR and 3' and 5'-RACE. The probe generated from this clone hybridized to a transcript approximately 1960 bp in length on northern blots. The clone encodes for a deduced protein 594 amino acids in length with 73% identity, 83% similarity to purH from Drosophila melanogaster. Northern blot (total RNA) analysis determined that L. decemlineata purH (LdpurH) was downregulated in diapausing beetles stored at 10°C. Developmental studies revealed that LdpurH is expressed at nearly constant high levels in both nondiapausing and prediapause adults. LdpurH expression during the first 20 days of diapause is equivalent to that seen in nondiapausing beetles, after which expression decreases. Exposing 70 day old diapausing beetles to 20°C for 24 h induced an increase in expression of purH indicating that purH is regulated by temperature in diapausing/overwintering beetles.

Diapausing Colorado potato beetles are devoid of short neuropeptide F I and II

An extract of head ganglia and retrocerebral complexes of nondiapausing and diapausing Leptinotarsa decemlineata was prepared to characterize regulatory neuropeptides involved in adult diapause by using a differential peptidomics approach. To reduce sample complexity, both extracts were roughly separated by means of an identical chromatographic step. MALDI-TOF MS led to the identification of proctolin, an adipokinetic hormone, and short neuropeptide F I and II in the extract of nondiapausing beetles. In combination with nano-ESI-Q-TOF MS 2 evidence was found for the presence of three pyrokinins, the first to be identified in a coleopteran species. Pyrokinins, involved in the induction of embryonic diapause in Bombyx mori, were present in both physiological conditions suggesting that they are of minor importance in the regulation of adult diapause in the Colorado potato beetle. A striking difference, detected by the differential peptidomics approach, between both neuropeptide profiles was the absence of ions corresponding to the short neuropeptide F (sNPF) related peptides, also known as Led-NPF-I and -II, in the extract of diapausing animals. Therefore, we postulate that “short NPFs” are involved in the regulation of adult diapause, displayed by the Colorado potato beetle.

Photoperiod and temperature affect the life cycle of a subtropical cockroach, Opisoplatia orientalis: seasonal pattern shaped by winter mortality

Abstract. Opisoplatia orientalis is an ovoviviparous cockroach living in the subtropical areas in Japan. Both adults and nymphs overwinter on Hachijo Island (33°N). The nymphs sampled before and after overwintering showed a similar pattern in frequency distribution of head widths with a definite peak of fifth instars. The present study was conducted to determine how this pattern was formed by investigating the effects of photoperiod and temperature on development and reproduction. Photoperiod influenced the number of nymphal instars, resulting in a longer duration of nymphal development at LD 12 : 12 h than at LD 16 : 8 h. However, the rate of development at each instar was only affected to a small extent by photoperiod and no sign of diapause was detected. It was suggested that the photoperiodic response controlling the number of nymphal instars might have evolved to adjust the timing of adult emergence and reproduction to the favourable season. The prereproductive period and time intervals between nymph depositions were prolonged as temperature declined, but there was no evidence for diapause in adults. Mortality occurred in eggs and embryos inside of the body of the females during winter. Thus, it was inferred that female adults would reset ovarian development in spring and deposit nymphs in summer simultaneously, and these nymphs would reach the fifth instar before winter comes. This winter mortality hypothesis was supported by experiments in which reproductive activity and mortality were monitored for field‐collected adults under either constant or changing temperature conditions simulating those in the field.

Environmental factors that determine the seasonal onset and termination of reproduction in seed-sucking bugs (Heteroptera) in Japan

The onset and termination of reproductive seasons in insects are determined by various environmental factors under natural conditions. These factors will be reviewed in seed-feeding heteropterans that have winter adult diapause in Japan. Most species use photoperiod to time the induction of adult diapause and therefore the termination of reproduction in autumn. In some species, however, temperature or the quality of food are also used as seasonal cues. For initiation of reproduction in spring, a temperature increase above the lower thermal threshold for postdiapause development is essential. The appearance of host plant seeds primarily determines the onset of reproduction in Dybowskyia reticulata, and the photoperiod plays a definitive role in Cletus punctiger. However, the proximate factors that determine the onset of reproduction in spring have not been examined as intensively as those for the termination of reproduction in autumn.

Termination of reproductive diapause in the rice water weevil with particular reference to the effects of temperature

The period of diapause termination in adults (collected in Yueqing 120.94°E, 28.14°N, Zhejiang) of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), were determined by initially exposing diapausing adults to various constant temperatures (25–5°C) as well as to room temperatures (33–−1°C), and then transferring them at intervals to a climatically controlled chamber (26±1°C, using rice seedlings as adult hosts) where the dynamics of oviposition onset and the numbers of eggs deposited were observed. Under room temperature, the diapause in 1st- and 2nd-generation adults terminated around late September and early December, respectively, i.e. at ca. 2.5 and 2.0 months after collection. Diapause in both 1st- and 2nd-generation adults was significantly affected by temperature. When exposed to 10, 15 and 20°C, the diapause in most 1st-generation adults terminated after 75, 25 and 50 days, respectively, while in 2nd-generation adults it terminated after 50 days at each of these temperatures. The associated adaptive significance and geographical variation of diapause termination in this insect are discussed.

Heat-shock-responsive genes are not involved in the adult diapause of Drosophila triauraria.

Although the molecular regulation of diapause remains largely unknown, there is an accumulation of data suggesting the involvement of heat-shock proteins in the expression of diapause or dormancy. However, Goto et al. [J. Insect Physiol. 44 (1998) 1009] reported that Drosophila triauraria does not express Hsp70 transcripts at normal temperatures, regardless of the diapause state. Here, we investigated the transcriptional regulation of other heat-shock-responsive genes (Hsp23, Hsp26, Hsp83 and Hsrw) in D. triauraria with relation to diapause. The results revealed that these genes are not regulated as a function of diapause, suggesting that they are not involved in the expression of diapause in this species.

Timing of diapause induction and its life‐history consequences in Nezara viridula: is it costly to expand the distribution range?

Abstract. 1. From the early 1960s to 2000 Nezara viridula (Heteroptera: Pentatomidae) expanded its range northwards in Japan and reached Osaka following climate warming recorded in the region.2. The timing of diapause induction and its effect on life‐history traits were studied under quasi‐natural conditions in Osaka. Egg masses were placed outdoors in six series in July–November 1999. Developmental events were monitored until September 2000.3. Adult diapause was induced in September–October in agreement with the photoperiodic response obtained under laboratory conditions. Induction of diapause in early October ensured the highest winter survival. Nymphs that hatched after late September died by December–April showing that the species cannot survive winter in the nymphal stage.4. Life‐history traits varied between the early (non‐diapause reproduction) and late (post‐diapause reproduction) series. Thus, non‐diapause females produced significantly fewer egg masses than did females that reproduced only after diapause. The timing of diapause induction strongly affected overwintering success and post‐diapause performance: females that became adults and entered diapause in October lived longer, had a longer period of oviposition, and produced more eggs in larger egg masses than females that attained adulthood and entered diapause in September.5. Females from the early series reproduced until late November, although progeny from the late September eggs were destined to die during the winter. Pre‐winter reproduction of adults that emerged in mid‐September or later was a result of the imperfect timing of diapause induction. It is an ineffective allocation of resources and may be considered the ecological cost of range expansion.6. To establish in the region, N. viridula will probably evolve a lengthening of the critical photoperiod of the diapause induction response. This will allow the species to enter diapause earlier and, thus, avoid maladaptive late‐autumn reproduction but, perhaps, increase the cost of diapause because of a possible adverse impact of pre‐winter high temperature conditions on overwintering.

Presence of three diapauses in a subtropical cockroach: control mechanisms and adaptive significance

Abstract. Diapause is common among insects and is regarded as an adaptive response to periodic occurrence of adverse conditions. It occurs at a particular developmental stage, typically only once in a lifetime. However, little is known about the details of the control mechanism of life cycles with multiple diapauses in insects. In this study, a complex 2‐year life cycle with three types of diapause is reported in a subtropical cockroach, Symploce japonica: a winter diapause in mid‐nymphal instars, a summer diapause in later nymphal instars, and a reproductive diapause is reported in the adult stage. Nymphal development was extremely slow either at short days (winter diapause) or long days (summer diapause). Nymphs in summer diapause matured rapidly when transferred from long days to short days, indicating that seasonal changes in day‐length are the pivotal factor in the control of this life cycle. It is proposed that the main significance of winter diapause in this subtropical species is to enable the nymphs to survive the mild winter successfully with reduced energy demand, and that of summer diapause is to delay adult emergence until late in the autumn for successful induction of the following adult diapause. Adults do not emerge until shortly before winter, yet the presence of diapause in the adult stage does not simply appear to be a response to cope with the winter conditions but, instead, ensures that reproduction will occur early the next year, before summer, because reproduction is greatly hampered at high temperature.

Photoperiodic and temperature control of diapause induction and colour change in the southern green stink bug Nezara viridula

Abstract. The effect of photoperiod and temperature on the duration of the nymphal period, diapause induction and colour change in adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) from Japan was studied in the laboratory. At 20 °C, the developmental period for nymphs was significantly shorter under LD 10 : 14 h (short day) and LD 16 : 8 h (long day) than under intermediate photoperiods, whereas at 25 °C it was slightly shorter under intermediate than short‐ and long‐day conditions. It is assumed that photoperiod‐mediated acceleration of nymphal growth takes place in autumn when day‐length is short and it is unlikely that nymphal development is affected by day‐length under summer long‐day and hot conditions. Nezara viridula has an adult diapause controlled by a long‐day photoperiodic response. At 20 °C and 25 °C in both sexes, photoperiodic responses were similar and had thresholds close to 12.5 h, thus suggesting that the response is thermostable within this range of temperatures and day‐length plays a leading role in diapause induction. Precopulation and preoviposition periods were significantly longer under near‐critical regimes than under long‐day ones. Short‐day and near‐critical photoperiods induced a gradual change of adult colour from green to brown/russet. The rate of colour change was significantly higher under LD 10 : 14 h than under LD 13 : 11 h, suggesting that the colour change is strongly associated with diapause induction. The incidences of diapause or dark colour did not vary among genetically determined colour morphs, indicating that these morphs have a similar tendency to enter diapause and change colour in response to short‐day conditions.

First evidence for photoperiodic regulation of the life cycle in a millipede species, Polydesmus angustus (Diplopoda: Polydesmidae)

The hypothesis that the periods of dormancy previously described in the millipede Polydesmus angustus may be photoperiodically induced diapauses was tested experimentally. In this species, biennial individuals exhibit two successive periods of dormancy: aestivation in the penultimate stadium (stadium VII) and reproductive dormancy in the adults, which emerge in autumn. It was first established that the reproductive dormancy is not a thermally controlled state of quiescence. When adults emerging in autumn were kept at 16 °C under natural photoperiod, their reproduction was delayed for several months in comparison with adults emerging in spring at similar temperatures. This indicates that the reproductive dormancy begins with a period of diapause. Further experiments provided evidence of a photoperiodic induction of the adult diapause. When millipedes were reared under short day length (L:D 12:12 h) throughout their development, they required more time to reproduce than millipedes reared under long day length (L:D 16:8 h) at the same temperatures. Photoperiod influenced reproduction in females, but no significant effects were detected in adult males. On the other hand, stadium VII was markedly longer at L:D 16:8 h than at L:D 12:12 h in both sexes, which strongly suggests that aestivation is also induced by photoperiod. However, the effects on the duration of stadium VII varied among individuals, some of which showed no response to long days. This study is the first to document photoperiodic regulation of the life cycle in the class Diplopoda, a trait common in other classes of terrestrial arthropods.