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.     

Dispersion of flightless adults of the Asian lady beetle, Harmonia axyridis, in greenhouses containing cucumbers infested with the aphid Aphis gossypii: effect of the presence of conspecific larvae

Nezara viridula (L.) (Heteroptera: Pentatomidae) recently expanded its distribution range in Japan and reached Osaka. In the southern temperate zone, the species overwinters in the adult stage and reproductive diapause is associated with a body colour change from green to russet. In Osaka, the reproductive diapause is only induced in September–October and nymphs from late egg masses are destined to die during winter. However, the fate of adults emerging late in the season remained unknown. Survival, body colour change, and post‐diapause reproduction were studied under quasi‐natural conditions in Osaka in 1999–2000 in those adults that attained adulthood as late as in November. Two experimental cohorts were used: in the Outdoor cohort, insects were reared outdoors starting in their second instar (28 September); in the Laboratory cohort, nymphs and subsequently adults were reared from the same day under diapause‐inducing conditions (L10:D14 at 25 °C), then acclimatized (5 days at 20 °C and 5 days at 15 °C; L10:D14) and transferred outdoors on 1 December. Adults in both cohorts did not reproduce in autumn and survived the winter with a low mortality. More than 20% of adults in the Outdoor cohort failed to change body colour from green to russet during winter, apparently because of the low ambient temperature, suggesting that the environmental conditions required for colour change do not completely coincide with those required for diapause induction, and that the colour of the adults is not always a reliable indicator of diapause in this species. After overwintering, females from the Outdoor cohort produced significantly fewer egg masses and eggs and had a significantly shorter period of oviposition than females that entered diapause under short‐day conditions in the Laboratory cohort. Thus, if progeny from the late egg masses attain adulthood late in the autumn, these adults have high chances of successful overwintering, but their reproductive output after the winter diapause is significantly reduced.     

Dissecting insect responses to climate warming: overwintering and post‐diapause performance in the southern green stink bug,Nezara viridula,under simulated climate‐change conditions

The effect of simulated climate change on overwintering and post‐diapause reproductive performance is studied in Nezara viridula (L.) (Heteroptera: Pentatomidae) close to the species' northern range limit in Japan. Insects are reared from October to June under quasi‐natural (i.e. ambient outdoor) conditions and in a transparent incubator, in which climate warming is simulated by adding 2.5°C to the ambient temperatures. Despite the earlier assumption that females of N. viridula overwinter in diapause, whereas males do so in quiescence, regular dissections show that the two sexes overwinter in a state of true diapause. During winter, both sexes are dark‐coloured and have undeveloped reproductive organs. Resumption of development does not start until late March. During winter, the effect of simulated warming on the dynamics and timing of physiological processes appears to be limited. However, the warming significantly enhances winter survival (from 27–31% to 47–70%), which is a key factor in range expansion of N. viridula. In spring, the effect of simulated warming is complex. It advances the post‐diapause colour change and transition from dormancy to reproduction. The earlier resumption of development is more pronounced in females: in April, significantly more females are already in a reproductive state under the simulated warming than under quasi‐natural conditions. In males, the tendency is similar, although the difference is not significant. Warming significantly enhances spring survival and percentage of copulating adults, although not the percentage of ovipositing females and fecundity. The results suggest that, under the expected climate‐warming conditions, N. viridula will likely benefit mostly as a result of increased winter and spring survival and advanced post‐diapause reproduction. Further warming is likely to allow more adults to survive the critical cold season and contribute (both numerically and by increasing heterogeneity) to the post‐overwintering population growth, thus promoting the establishment of this species in newly‐colonized areas.     

Seasonal changes in the reproductive and life-history traits of Chrysomela populi L. (Coleoptera: Chrysomelidae)

Seasonal changes in the reproductive and life‐history traits of Chrysomela populi L. were investigated in Shobara (34°52′N, 133°01′E), Japan, in 2004 and 2005. Larvae were hatched and reared under natural photoperiod and temperature in 8 different periods between late April and early September in 2004. The incidence of adult diapause increased with progression of the season in 2004. The critical timing of diapause induction, as defined by 50% of females entering diapause, was estimated to occur between late July and early August. No effects of season on the survival rate from hatching to adult emergence, percentage ovipositing females and percentage females that deposited viable eggs were clearly detected. Adult weight at emergence fluctuated seasonally, which was probably caused by air temperature. No effect of season on the oviposition period was observed among females that averted diapause. Females that entered diapause in 2004 started oviposition from the first day of May in 2005. Reproductive output was significantly greater in diapause females than in non‐diapause females. This increase in the reproductive output of diapause females was caused by elongation of the oviposition period and consequently by enlargement of the number of egg clutches deposited. These results suggest that the seasonal timing of diapause induction in females of C. populi would be affected by various risks and benefits to reproduction and survival.     

Surviving winter: diapause syndrome in the southern green stink bug Nezara viridula in the laboratory,in the field,and under climate change conditions

The southern green stink bug Nezara viridula (L.) (Heteroptera: Pentatomidae) has long attracted attention not only as a serious pest of numerous agricultural crops, but also as a species expanding its range in many parts of the world. Nezara viridula has also been widely used as a model in different experimental studies. The present review focuses on reproductive (i.e. adult) winter diapause, which is the pivotal element of the species' seasonal cycle. Results from numerous field experiments and observations, as well as laboratory ecophysiological investigations conducted during the few last decades, are analyzed and interpreted. Experimental findings are used to describe in detail the dynamics of physiological changes during overwintering. Reproductive diapause in N. viridula is controlled in both sexes by photoperiodic conditions. The induction of diapause is associated with a reversible change of body colour from green or yellow to russet (or brown). The proper timing of adult emergence and the induction of diapause, as well as the size of adults, is vitally important for successful overwintering. Nezara viridula has been shown to respond strongly to the current trend in climate change by shifting the limit of its northern range, particularly in central Japan. Analysis of historic climate data suggests that the environmental conditions during the last few decades have become more favourable for the overwintering survival of N. viridula in many locations in central Japan. This has likely promoted the northward spread of the species. The relationships between reproductive diapause, reversible body colour change, overwintering success and the recent range expansion are analyzed. Perspectives of the range dynamics of the species are discussed in light of further predicted climate change.     

Photoperiodic response in the subtropical and warm‐temperate zone populations of the southern green stink bug Nezara viridula: why does it not fit the common latitudinal trend?

The photoperiodic response of diapause induction is studied in females of five subtropical and warm‐temperate zone populations of Nezara viridula (L.) (Heteroptera: Pentatomidae) in Japan (26.4–34.7°N; 127.4–135.7°E). Laboratory tests at 25 °C demonstrate that both warm‐temperate and subtropical populations have pronounced photoperiodic responses of adult diapause induction. Under short‐day conditions (LD 10 : 14 h), 73–100% of females enter diapause, whereas, under long‐day conditions (LD 15 : 9 h), 87–100% of females are nondiapause and reproduce. When the critical photoperiod for diapause induction is plotted against the latitude of origin of each population, the data points do not show the expected tendency of increasing critical photoperiod northwards but, instead, vary between 12 h 15 min and 13 h 30 min. It is suggested that adults from different populations of such a highly migratory species move often among subtropical islands (by themselves or being assisted by typhoons), thus constantly destabilizing the photoperiodic responses. Although important for general synchronization of seasonal development in the tropics and subtropics, winter diapause might not be so critical for survival in mild winters in these zones. Such circumstances might make the selective pressure over the photoperiodic response less severe in the tropics and subtropics than in the temperate zone. It is suggested that the current climate warming might contribute to this situation as well by promoting polewards migrations and lessening the selective pressure of overwintering conditions.     

Some like it hot! Rapid climate change promotes changes in distribution ranges of Nezara viridula and Nezara antennata in Japan

We compared past and current limits of the distribution range of the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae), in central Japan. In the early 1960s, the northern limit of the range was in Wakayama Prefecture and was limited by a +5 °C isothermal line for the mean January temperature. In 2006–2007, a new survey demonstrated that this northern limit had shifted northwards by 85 km (i.e., at a mean rate of 19.0 km per decade). The shift was most likely promoted by milder winter conditions. The mean January to February temperature in the region was 1.03–1.91 °C higher in 1998–2007 than in 1960–1969. The number of cold days (with the mean temperature below +5 °C) also significantly decreased, while the annual lowest temperature significantly increased. Nezara viridula was found mostly close to those locations where (i) the mean January temperature exceeded +5 °C, (ii) the mean number of cold days did not exceed 26 in January to February, and (iii) where the mean annual lowest temperature did not drop below –3.0 °C. The general linear model shows that the mean January temperature and number of cold days are the most important factors controlling the northern limit of distribution of N. viridula. All the climatic data suggest that over the last 45 years, environmental conditions have become more favourable for overwintering of N. viridula at many locations in central Japan. This has probably promoted the northward spread of the species, representing a direct response to climate warming. A sympatrically distributed congeneric, Nezara antennata Scott, seems to respond to the warming by a retreat from the ocean coast towards cooler elevated habitats, which might be a complex response to elevated temperature and interspecific mating with N. viridula. It is suggested that the range changes in both species will continue in response to further climate change.     

Impact of increasing temperatures and exposure duration on egg hatch in the hemlock looper,Lambdina fiscellaria

As the growing season is expected to begin earlier under climate change, insects should initiate reproduction several days or weeks earlier than they used to. In eastern Canada, hemlock looper (HL) Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) females generally oviposit in September, with eggs entering an obligatory diapause quickly after their deposition. We therefore simulated an early start of the HL reproduction cycle of 2, 4, 6, or 8 weeks to examine the extent to which freshly laid eggs from two populations (island and mainland) can withstand exposure to four temperature conditions (15, 20, 25 °C, or fluctuating temperature in an outdoor insectary), with all treatments ending on 1 September 2007. On this date, half the eggs from each population were immediately incubated at 15 °C, while the rest were stored in an outdoor insectary until their incubation at 15 °C the following spring. In a separate experiment, the effect of temperature on pre‐diapause duration was determined from the number of days required for eggs to change colour after oviposition. The pre‐diapause phase was completed faster as temperature increased. Regardless of incubation date and population, percent hatch decreased significantly after 6‐8 weeks of exposure to 25 °C or in the outdoor insectary. Under most treatments, the odds of dying as pharate larvae increased with exposure duration. When eggs were incubated at 15 °C immediately after treatment, time to hatch and diapause duration remained constant over treatments, except at 25 °C when they both decreased. After 8 weeks of exposure to 15 or 20 °C, eggs transferred outdoors were more likely to hatch precociously than those exposed to 25 °C or insectary conditions. Globally, mortality seemed greater among eggs stored outdoors than among those kept indoors. Most eggs that survived the winter hatched synchronously after incubation in spring. Overall, larger eggs from the island population survived better than smaller eggs from the mainland population.     

Alternative life cycles controlled by temperature and photoperiod in the oligophagous bug, Dybowskyia reticulata

Abstract. Effects of temperature and photoperiod on the induction and re-induction of adult diapause were examined in Dybowskyia reticulata (Dallas) (Heteroptera: Pentatomidae). Adults collected from the field after overwintering in early summer continued oviposition under long-day conditions of LD 16:8 h at 20 or 25°C, while they re-entered diapause under short-day conditions of LD 12:12 h at 25, 27.5 or 30°C. By contrast, adults reared in the laboratory from eggs at 20 or 25°C entered diapause under both long-day and short-day conditions, whereas those reared at 27.5 and 30°C entered diapause only under short-day conditions. Under quasi-natural conditions in 1993, when summer temperature was low, most adults of the first generation entered diapause in late July. However, in the warmer summer of 1996, oviposition was recorded in many females that ecdysed into adults from July to early August. Even though the seeds of the host plants occur in a restricted period from early summer to early autumn, in warmer years D. reticulata may produce a second generation. The response to temperature with a threshold between 25 and 27.5°C in D. reticulata brings about a switch between the univoltine and bivoltine life cycles.     

Seasonal occurrence and diapause induction of a predatory bug Andrallus spinidens (F.) (Heteroptera: Pentatomidae)

The bug Andrallus spinidens (F.) (Heteroptera: Pentatomidae) is a polyphagous predator of insect larvae, which is distributed in tropical and warm temperate zones worldwide. Seasonal occurrence and diapause induction of this bug were studied in a population in Miyazaki, southern Kyushu, Japan. The field research showed that A. spinidens produces three or four generations a year and is most abundant from mid‐summer to autumn. Reproductive activity of field‐collected adults decreased from late summer to autumn, indicating that this bug enters adult diapause in autumn. Only adults were found in early spring and these were reproductive. Laboratory experiments showed that, irrespective of photoperiod, adult diapause is induced at lower temperatures (≤22.5°C), whereas it is avoided at higher temperatures (≥25°C). Ambient temperature falls across the critical range from late summer to autumn. Thus, the bug clearly overwinters in adult diapause induced by low temperatures and this diapause is terminated during the course of winter.     

Induction of adult diapause and of low and high reproductive states in a parasitoid wasp,Ooencyrtus nezarae, by photoperiod and temperature

Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) was reared on eggs ofRiptortus clavatus (Thunberg) (Heteroptera: Alydidae) at various temperatures under long-day (L16:D8) or short-day (L10:D14) conditions. There was no diapause during egg, larval or pupal stages under any set of conditions examined. However, at 15°C under short-day conditions, vitellogenesis was arrested in all adult females and they entered diapause. At 15°C under long-day conditions, or at 20°C under short-day conditions, some adult females entered diapause. Under the latter set of conditions, the adult females laid eggs but they laid fewer eggs than under long-day conditions, Even at 25°C, under short-day conditions, adult females laid fewer eggs than under long-day conditions, and this low rate of oviposition was attributed to the retarded development of ovaries. Diapause adults reared at 15°C were more resistant to low temperature than nondiapause adults reared at 25°C.     

Changes in life‐history traits of the water strider Aquarius paludum in accordance with global warming

Seasonal records of nymphs of the water strider Aquarius paludum Fabricius (Heteroptera: Gerridae) at a waterway in Kochi prefecture, Japan (33°00′N to 33°30′N), in 2007, show that populations of new generation adults occur four or more times during the year, in mid and late May; late July to early August; September; and October to November. In laboratory experiments, more than 50% of adults are reproductive, irrespective of photoperiod, and this ratio increases to 80% even under a short‐day LD 11.5 : 13.5 h photocycle, which corresponds to the winter season at Kochi (33°N). There is a diminishing photoperiodic response in relation to the induction of diapause compared with measurements made in previous years (1995–1997), suggesting that reproduction may be possible over a much longer period in the near future (and even in winter) if local climate warming is sustained. A high proportion of males sampled in 2008 have small testes and a high proportion of females do not have mature oöcytes even in summer. This contrasts with earlier data showing that the testis volume index for the same period is greater in 1995–1997, and that 75% of females have mature oöcytes. These changes suggest that the Kochi‐Nankoku population of A. paludum is beginning to show partial aestivation. Overwintering adults of both sexes are found to have no mature flight muscles in October/November 2008. This is in marked contrast with earlier data from 1995 and 2004. Adults that are reared in the laboratory also show a lower flight propensity in response to shorter day lengths. The absence of mature flight muscles in the autumn and lower flight propensity under shorter days may indicate a cessation of dispersal between the summer habitats and overwintering sites on land far from the waterways. Taken together, these data suggest that populations of A. paludum in the Kochi‐Nankoku region are continuing to show adaptive changes, apparently in relation to global warming.     

Diapause induction and termination in a commonly univoltine leaf beetle (Phratora vulgatissima)

Abstract The leaf beetle Phratora vulgatissima (Linnaeus 1758) is commonly univoltine in south‐central Sweden but may sometimes initiate a partial second generation. The current study was set out to investigate under what abiotic conditions the beetles initiate a second generation. Using climate chamber experiments, the beetles were shown to have a facultative reproductive diapause induced by declining day‐length. The critical day‐length (CDL) for diapause induction was estimated to be 18 h and 10 min. In the field, first‐generation beetles developing to adulthood before August in 2009 became reproductively active and produced a second generation, but most individuals emerged later and were in reproductive diapause. P. vulgatissima overwinter as adults and diapause was shown to be maintained until mid‐winter in 2008/2009. The cumulative temperature requirement for oviposition after diapause termination was estimated to be 222 day‐degrees with a 5.5°C temperature threshold. Three different day‐degree models that were developed to predict the phenology of female oviposition in the spring were validated by comparing model results with field data on the timing of oviposition in previous years. The study suggests that P. vulgatissima may initiate a second generation in Sweden if development of the first generation is completed before August. Warmer spring and summer temperatures due to ongoing climate change may cause advanced insect phenology and faster completion of insect life‐cycles at northern latitudes, which will affect the proportion of insects that initiate a second generation.     

Photoperiodic and temperature control of nymphal development and induction of reproductive diapause in two predatory Orius bugs: interspecific and geographic differences

Abstract The effects of day‐length and temperature on pre‐adult growth and induction of reproductive diapause are studied in Orius sauteri and Orius minutus (Heteroptera: Anthocoridae) from northern (43.0°N, 141.4°E) and central (36.1°N, 140.1°E) Japan. In the north, at 20 °C, pre‐adult growth is slower under an LD 14 : 10 h photoperiod than under shorter or longer photophases. At 24 and 28 °C, the longer photophases result in shorter pre‐adult periods. Acceleration of nymphal growth by short days in autumn appears to be adaptive. In the central region, this response is less pronounced, suggesting that timing of adult emergence is less critical than in the north. Day length also influences the thermal requirements for pre‐adult development. The slope of the regression line representing temperature dependence of pre‐adult development is significantly smaller and the lower development threshold (LDT) is significantly lower under an LD 12 : 12 h photoperiod than under long‐day conditions. The weaker dependence of nymphal growth on temperature and the lower LDT in autumn might be adaptive. In the north, increased temperature shifts the critical day length of diapause induction and suppresses the photoperiodic response in O. sauteri but not in O. minutus. Further south, the incidence of diapause in both species is low even under short‐day conditions but the same interspecific difference is observed (i.e. increase of temperature affects the response in O. sauteri but not in O. minutus). This suggests seasonally earlier diapause induction with weaker temperature dependence in O. minutus than in O. sauteri.     

Selection for an optimal monovoltine life cycle in an unpredictable environment. Studies on the beetleCatops nigricans Spence (Col., Catopidae)

Summary Catops nigricans reproduces in the autumn. Pre-imaginal development is temperature-dependent and takes place during the winter, followed by aestivation in the early adult stage. This summer diapause is obligatory and temperature independent. It synchronizes the monovoltine life cycle with the annual cycle. In three populations collected near Kiel (54°22′ N, 10°6′ E), K?ln (50°54′ N, 7°6′ E), and Paris (49°25′ N, 2°20′ E), pre-imaginal development slowed and the duration of summer diapause decreased with increasing latitude. Synchronization of the critical breeding interval with the appropriate environmental conditions was achieved through temperature- and photoperiod-dependent sensitivity of ovipositing adults, through different thermal thresholds in eggs, larvae, and pupae, and through sensitivity to photoperiod in third-instars larvae.C. nigricans copes with the unpredictability of climatic conditions in different ways. The local populations have evolved a mean diapause length which probably adjusts the life cycle in most years to the optimal date for reproduction. The mean diapause length was 77 days for Kiel, 98 days for K?ln and 138 days for Paris at 10°C, short-day (=SD).C. nigricans also spreads the risk by varying diapause length. Amongthe progeny of single females the range of diapause duration covered about 70% of the total range of the whole population. The oviposition rate of females confined to subterranean life was the same as females confined to subterranean life was the same as in those living under the influence of a varying photoperiod.C. nigricans should therefore be able to live both in the litter layer of forests and also in the nests and galleries of small mammals.     

Effects of diet, photoperiod and temperature on the postdiapause reproduction in the cabbage bug,Eurydema rugosa

InEurydema rugosa Motschulsky (Heteroptera: Pentatomidae), the type of food supplied (i.e. seeds or leaves of the brown mustard,Brassica juncea Hemsel) and photoperiod, which control the induction of adult diapause, do not play a role in the initiation of reproduction after overwintering. A temperature above 13.2°C was required to start reproduction. After its initiation, however, short-day conditions on seeds induced diapause again in some adults. Although a diet of seeds under long-day conditions, in common with short-day conditions, induced diapause in young adults (Numata & Yamamoto, 1990), it did not reinduce diapause in adults after overwintering. Thus,E. rugosa that had overwintered became sensitive to diapause-inducing photoperiod again but not to dietary factors.     

Effects of photoperiod and temperature on reproductive diapause in Ophraella communa (Coleoptera: Chrysomelidae), a potential biocontrol agent against Ambrosia artemisiifolia

Abstract To investigate the seasonal adaptation strategies of Ophraella communa to new habitats, the effects and regulation mechanisms of photoperiod and temperature on the reproductive diapause in a population collected from Changsha, Hunan were examined. Adults showed obvious reproductive diapause, which was regulated by photoperiod and temperature. At 30°C, there was no adult diapause occurring under either long‐day or short‐day conditions; at 25°C the pre‐oviposition period was short and fecundity was high in adult females under L : D 16 : 8 h, whereas under L : D 12 : 12 h, a few females entered reproductive diapause; at 20°C under short‐day conditions, all female adults entered diapause. The pre‐oviposition period was significantly prolonged when the pupae and adults were transferred from long‐days to short‐days, but the day length influence was not obvious when they were transferred only in the adult stage. However, the fecundity dropped greatly no matter whether the photoperiod shifted to short‐days only in the adult stage or whether the shift occurred in both the pupal and adult stage. The fecundity was extremely low when photoperiod shifted from long‐days to short‐days in both pupal and adult stages. This was an indication that the pupal and adult stages were the photoperiod‐sensitive stage for adult reproductive diapause. This was especially true for the photoperiod in the pupal stage, which has a distinctly significant regulative effect on reproductive diapause. Additionally, this article also addresses the reason for different photoperiodic response patterns in reproductive diapause induction between the Changsha strain and the Tsukuba strain (Japan) of O. communa.     

Efficient strategies for changing the diapause character of silkworm eggs and for the germline transformation of diapause silkworm strains

Abstract To overcome the disadvantages of current silkworm Bombyx mori transgenic technology, such as costly and time‐consuming to maintain non‐diapause transgenic silkworms, we report here on the development of treatments for the germline transformation of diapause silkworm strains. Our results showed that HCl treatment within 3 h of oviposition was able to prevent the diapause of eggs from Japanese lineage diapause silkworm strains and was also suitable for germline transformation of the same strains. By incubating developing mother eggs from Chinese lineage diapause silkworm strains at 15°C (15°C‐IME), we were able to prevent the diapause of their daughter eggs; a similar strategy (15°C‐IMES) for the germline transformation of the same strains was that the mother eggs were incubated at 15°C, and the daughter eggs were then microinjected according to the conventional microinjection methods used for non‐diapause eggs. By combining temperature and light controls, the improved 15°C‐IMES strategy prevented diapause in daughter eggs, and also enabled the germline transformation of both Japanese and Chinese lineage diapause silkworm strains. Although each of the strategies developed here has advantages and disadvantages, we suggest that the 15°C‐IMES strategy is a good reference for the establishment of germline transformation technologies of other egg diapause insects. These new strategies for the efficient germline transformation of diapause silkworm strains are likely to improve the practical use of silkworm transgenic lines in sericulture and also highlight silkworm functional genomics research and its modeling.     

Inheritance of photoperiodic induction of larval diapause in the Asian corn borer Ostrinia furnacalis

The Asian corn borer Ostrinia furnacalis (Guenée) enters facultative diapause as fully‐developed larvae in response to short‐day conditions. As a consequence of geographical variation in photoperiodic response, moths from Nanchang (28°46′N, 115°50′E) enter diapause in response to short day‐lengths (D strain), even at the high temperatures whereas moths from Ledong (18°47′N, 108°89′E) exhibit almost no diapause under the same conditions (N strain). In the present study, crosses between the two strains are used to evaluate the inheritance of diapause under different photoperiods at temperatures of 22, 25 and 28 °C. The moths, both reciprocal crosses and backcrosses, show a clear long‐day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. However, the critical day‐length for induction of diapause is shorter in hybrids than in the D strain. The N strain also shows a short‐day photoperiodic response at the lower temperature of 22 °C, indicating that the N strain still has the capacity to enter a photoperiodically‐induced diapause, depending on the rearing temperature. The incidence of diapause in all crosses is highest with D strain fathers or grandfathers and lowest with N strain fathers or grandfathers, indicating that the male parent has significantly more influence on the incidence of diapause of subsequent progeny than the female. The results obtained from all crosses under LD 12 : 12 h or LD 13 : 11 h photocycles at 25 °C show that inheritance of diapause in O. furnacalis does not fit an additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance.     

Effects of photoperiod and temperature on the termination of diapause in the univoltine seed wasp Eurytoma plotnikovi

Abstract Mummified pistachios containing fully grown diapause larvae of Eurytoma plotnikovi Nikol'skaya (Hym., Eurytomidae) were collected in early August and late September in coastal northern Greece and subjected to various photoperiod and temperature treatments, then maintained at 19 or 26°C and a long-day (LD 16:8 h), a changing, or a short-day (LD 10:14 h) photoperiod until pupation. In larvae of early August (beginning of diapause) subjected for 20 weeks to 19°C under a long, a changing, or a short photophase, followed by 19°C and a long photophase, 50% of the larvae pupated after 24, 18 and 13 weeks respectively. After exposure for 20 or even 12 weeks to a short photophase and low temperatures (10 or 4°C), pupation occurred after only 7–8 weeks and was more synchronous. The ranges of temperature for diapause development and post-diapause morphogenesis overlap. After exposure for 12 weeks to short days and low temperature, larvae of late September pupated much sooner under long days than under short days and sooner at 26° than at 19°C. E.plotnikovi depends on both temperature and photoperiod for diapause development, low temperature having a strong favourable effect on the earlier part and long day on the later part of diapause. In a few larvae of another pistachio seed wasp, Megastigmus pistaciae Walker, after a long enough period of low temperatures, diapause was terminated normally at 26°C and long days, or at 19°C and long or short days.