Responses to stepwise photoperiodic changes for the larval diapause of the Indian meal moth Plodia interpunctella

Abstract The Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae) diapauses as a last‐instar (fifth) larva. At 30 °C, no larvae enter diapause under any photoperiodic conditions; at 25 °C, the photoperiodic response curve is a long‐day type with a critical length of approximately 13 h light; at 20 °C, diapause is induced moderately even under long days (> 13 h). Cumulative effects of short days or long days on diapause induction are determined by alternate, stepwise and gradually changing regimes of photoperiod at 25 °C. When the larvae are repeatedly exposed to LD 16 : 8 h and LD 12 : 12 h photoperiods every other day, the incidence of diapause is 37%. When the larvae are placed under an LD 16 : 8 h photoperiod for 2 days and then under an LD 12 : 12 h photoperiod for 1 day, it is 38 %. Exposure to an LD 16 : 8 h photoperiod for 1 day and then to an LD 12 : 12 h photoperiod for 2 days induces only 15% diapause. This may indicate that the photoperiodic information is not accumulated in a simple fashion despite the generally accepted hypothesis (i.e. photoperiodic counter). Larvae exposed to an LD 16 : 8 h photoperiod for 5 days after oviposition express a very high incidence of diapause even under short days between an LD 2 : 22 h and LD 12 : 12 h photoperiod. After 10 days exposure to an LD 16 : 8 h photoperiod, however, the short day does not induce diapause strongly. On the other hand, an LD 12 : 12 h photoperiod in the early larval life is highly effective in the induction of diapause. A gradual increase or decrease of photoperiod (2 min day^?1) shows that the direction of photoperiodic change does not affect the diapause determination.     

Effects of photoperiod and temperature on diapause induction and termination in the swallowtail,Sericinus montelus

Abstract Sericinus montelus overwinters as diapausing pupae. In the present study, the effects of photoperiod and temperature on diapause induction and termination of diapause are investigated. The results obtained demonstrate that high temperature can reverse the effect of short day‐lengths on diapause induction. Under an LD 12 : 12 h photoperiod, all pupae enter diapause at 15, 20 and 25 °C, whereas all pupae develop without diapause at 35 °C. No pupae enter diapause under an LD 14 : 10 h photoperiod when the temperature is above 20 °C. Photoperiodic response curves obtained at 25 and 30 °C indicate that S. montelus is a long‐day species and the critical day‐length is approximately 13 h at 25 °C. At 25 °C, the duration of diapause is shortest when the diapausing pupae are maintained under an LD 16 : 8 h photoperiod and increases under LD 14 : 10 h and LD 12 : 12 h photoperiods. Under an LD 16 : 8 h photoperiod, the duration of diapause is shortest when the diapausing pupae are maintained at 25 °C, followed by 20 and 30 °C, and then at 15 °C. These results suggest that a moderate temperature favours diapause development under a diapause‐averting photoperiod in this species. The duration of diapause induced by an LD 12 : 12 h photoperiod is significantly longer at 25 °C than those at 15, 20 and 30 °C, and is shortest at 15 °C. At 25 °C, the duration of diapause induced by LD 6 : 18, LD 12 : 12 and LD 13 : 11 h photoperiods is similar and longer than 90 days. Thus, the diapause‐inducing conditions may affect diapause intensity and a photoperiod close to the critical day‐length has significant influence on diapause intensity in S. montelus.     

Effect of daylength and temperature on the larval diapause of the sunflower moth, Homoeosoma electellum

The effect of daylength and temperature on the regulation of the larval diapause of a central Missouri population of the sunflower moth, Homoeosoma electellum, was examined. Fully grown fourth-instar larvae exhibit a facultative diapause. Measurements of the effect of photoperiod on diapause induction revealed critical photoperiods of about 13 h 30 min light/day at 20°C, and between 11 h 45 min and 12 h light/day at 23°C. Third and fourth-instar larvae were shown to be the main sensitive stages for diapause determination. Daylength was also shown to be an important regulator of the rate of diapause development. A short day of LD 10:14 h permitted only a low rate of diapause development, whereas long days of LD 14:10 h and LD 16:8 h accelerated diapause development at 25 and 30°C. When long days were alternated with short days at 30°C the accelerating effect of long days on diapause development was not found. Systematic transfers of chilled diapausing larvae revealed an accelerated diapause development in groups transferred from 10 to 30°C LD 10:14 h, but diapause development was not accelerated in groups transferred from 10 to 30°C LD 16:8 h.     

Induction and termination of prepupal summer diapause in Pseudopidorus fasciata (Lepidoptera: Zygaenidae)

The seasonal life cycle of the zygaenid moth, Pseudopidorus fasciata is complicated by two different developmental arrests: a winter diapause as a fourth larval instar and a summer diapause as a prepupa in a cocoon. Both larval diapause induction and termination are under photoperiodic control. Short days induce larval diapause with a critical daylength of 13.5h and long days terminate diapause with a critical daylength of 14h. In the present study photoperiodic control of summer diapause was investigated in Pseudopidorus fasciata. Under long photoperiods ranging from LD 14:10 to LD 18:6, only part of the population entered summer diapause, the rest continued to develop. The lowest number of prepupae entered diapause at LD 14:10, followed by LD 16:8 and LD 17:7. The highest incidence of diapause occurred with photoperiods of LD 15:9 and LD 18:6. By transferring the diapausing prepupae induced by various long photoperiods (LD 14:10, LD 15:9, LD 16:8, LD 17:7, LD 18:6) to LD 13:11, 25 degrees C, the duration of diapause induced by LD 14:10 was significantly shorter than those induced by longer photoperiods. By keeping aestivating prepupae induced by LD 15:9, 28 degrees C or by natural conditions at short photoperiods (LD 11:13 and LD 13:11) and at a long photoperiod (LD 15:9), the duration of diapause at LD 15:9 was more than twice as long as than those at LD 11:13 and LD 13:11. Moreover, adult emergence was highly dispersed with a high mortality at LD 15:9 but was synchronized with low mortality at LD 11:13 and LD 13:11. When the naturally induced aestivating prepupae were kept under natural conditions, the early aestivating prepupae formed in May exhibited a long duration of diapause (mean 126 days), whereas the later-aestivating prepupae formed in July exhibited a short duration of diapause (mean 69 days). These results indicate that aestivating prepupae require short or shortening photoperiod to terminate their diapause successfully. By transferring naturally induced aestivating prepupae to 25, 28 and 30 degrees C, the duration of diapause at the high temperature of 30 degrees C was significantly longer than those at 25 and 28 degrees C, suggesting that high temperature during summer also plays an important role in the maintenance of summer diapause in Pseudopidorus fasciata. All results reveal that summer diapause can serve as a "bet hedging" against unpredictable risks due to fluctuating environments or as a feedback mechanism to synchronize the period of autumn emergence.     

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.     

Photoperiodic and temperature effects on the intensity of larval diapause in Sesamia nonagrioides

Abstract. The intensity of larval diapause in Sesamia nonagrioides Lef (Lepidoptera: Noctuidae) was investigated under laboratory conditions. Newly hatched larvae were exposed to different stationary photoperiods (from LD 7 : 17 h to LD 14 : 10 h), at a constant temperature of 25 °C. Diapause incidence was higher when larvae were exposed to daylengths shorter than the critical value (LD 12 : 12 h), whereas the within‐treatment variation in the larval period appeared to be significantly correlated with the photoperiod applied. The incidences of diapause and the duration of larval development were also measured after exposing larvae to short photoperiods (LD 8 : 16 h, LD 10 : 14 h or LD 12 : 12 h) in combination with various temperatures (20, 22.5 or 25 °C). Although an increase in the incidence of diapause appeared with the lowering of the temperature, no statistical differences were observed in the time needed for pupation within the photoperiodic treatments at the temperatures of 20 and 22.5 °C. Furthermore, when diapausing larvae were transferred to the long photoperiod of LD 16 : 8 h, they immediately proceeded to pupation, regardless of the photoperiod or the temperature to which they had been previously exposed, indicating that there were no differences in the intensity of diapause. Photoperiodic changes from LD 10 : 14 h to LD 12 : 12 h or to LD 14 : 10 h at different larval ages reduced the intensity of diapause with (a) early age of transfer and (b) increase of daylength. By contrast, when larvae were transferred from the long photoperiod of LD 14 : 10 h to shorter, such as LD 10 : 14 h or LD 12 : 12 h, a small increase in the intensity of diapause with the shortening of the daylength was apparent. These results support the hypothesis that insects may compare the duration of the photoperiod and could classify them as either longer or shorter in relation to the critical value.     

Species specificity in photoperiodic control of nymphal development in four species of cricket from north-west China

Photoperiodic regulation of nymphal development was examined in four species of cricket collected in the Xinjiang‐Uygur Autonomy Region, China (approximately 43°N, 81–89°E). Fifty percent of individuals of Modicogryllus frontalis reared at 28°C reached adulthood in approximately 80 days in conditions of 11 h light : 13 h dark (LD 11:13) to 14:10, and in approximately 95 days under LD 15:9 to 16:8. Melanogryllus desertus started adult emergence earliest under LD 16:8 at 28°C, but some individuals required much longer to mature, and thus two peaks of adult emergence occurred at approximately 60 and 160 days after hatching. More individuals hatched during the late peak in LD 18:6 than in LD 16:8. The mean nymphal period was approximately 100 days in LD 11:13 to 14:10. Both species showed short‐day type photoperiodic responses, but Mo. frontalis developed faster than did Me. desertus. The latter occupied a wider range of habitat conditions and was more variable in life cycle than the former. Modicogryllus burdigalensis started adult emergence earliest in LD 16:8 at 28°C in the six photoperiods tested, most adults emerging within 60 days. The mean nymphal period was 80 days in LD 15:9, 135 days in LD 14:10 and 80–100 days in LD 11:13 to 13:11, showing an intermediate type of photoperiodic response. Acheta domesticus was a long‐day type species, and the proportion of delayed individuals increased with decreasing photoperiod. In the dry climate of Xinjiang‐Uygur, nymphal overwintering seems to be successful in all of the four different patterns of nymphal development.     

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.     

Photoperiodic control of diapause in Pseudopidorus fasciata (Lepidoptera: Zygaenidae) based on a qualitative time measurement

In the zygaenid moth, Pseudopidorus fasciata, both larval diapause induction and termination are under photoperiodic control. In this study, we investigated whether photoperiodic time measurement (with a 24-h light-dark cycle) in this moth is qualitative or quantitative. Photoperiodic response curves, at 22, 25, and 28 degrees C indicated that the incidence of diapause depended on whether the scotophases exceeded the critical night length (CNL) or not. All scotophases longer than the CNL-induced diapause; all scotophases shorter than the CNL-inhibited diapause. The CNL was 10.5h at 25 and 28 degrees C, and 10h at 22 degrees C. By transferring from various short photoperiods (LD 8:16, LD 9:15, LD 10:14, LD 11:13, LD 12:12, and LD 13:11) to a long photoperiod (LD 16:8) at different times, the number of light-dark cycles required for 50% diapause induction at 25 degrees C was 7.14 at LD 8:16, 7.2 at LD 9:15, 7.19 at LD 10:14, 7.16 at LD 11:13, and 7.13 at LD 12:12, without showing a significant difference between the treatments. Only at LD 13:11 (near the CNL), the number of light-dark cycles was significantly increased to 7.64. The intensity of diapause induced under different short photoperiods (LD 8:16, LD 9:15, LD 10:14, LD 11:13, and LD 12:12) at 25 degrees C was not significantly different with an average diapause duration of 36 days. The duration of diapause induced under LD 13:11 was significantly reduced to 32 days. All results indicate that the night-lengths are measured as either "long" or "short" compared with some critical value and suggest that photoperiodic time measurement for diapause induction in this moth is based on a qualitative principle.     

A comparison of photoperiodic control of diapause between aestivation and hibernation in the cabbage butterfly Pieris melete

In the cabbage butterfly, Pieris melete, summer and winter diapause are induced principally by long and short daylengths, respectively; the intermediate daylengths (12-13 h) permit pupae to develop without diapause. In this study, photoperiodic control of summer and winter diapause was systematically investigated in this butterfly by examining the photoperiodic response, the number of days required to induce 50% summer and winter diapause and the duration of diapausing pupae induced under different photoperiods. Photoperiodic response curves at 18 and 20 degrees C showed that all pupae entered winter diapause at short daylengths (8-11 h), the incidence of diapause dropped to 82.3-85.5% at 22 degrees C without showing a significant difference between short daylengths, whereas the incidence of summer diapause induced by different long daylengths (14-18 h) was varied and was obviously affected by temperature. By transferring from various short daylengths (LD 8:16, LD 9:15, LD 10:14 and LD 11:13) to an intermediate daylength (LD 12.5:11.5) at different times after hatching, the number of cycles required to induce 50% winter diapause (7.28 at LD 8:16, 7.16 at LD 9:15, 7.60 at LD 10:14 and 6.94 at LD 11:13) showed no significant difference, whereas by transferring from various long daylengths (LD 14:10, LD 15:9, LD 16:8 and LD 17:7) to an intermediate daylength (LD 12.5:11.5) at different times, the number of cycles required to induce 50% summer diapause (5.95 at LD 14:10, 8.02 at LD 15:9, 6.80 at LD 16:8, 7.64 at LD 17:7) were significantly different. The intensity of winter diapause induced under different short daylengths (LD 8:16, LD 9:15, LD 10:14 and LD 11:13) was not significantly different with an average diapause duration of 87 days at a constant temperature of 20 degrees C and 92 days at a mean daily temperature of 19.0 degrees C, whereas the intensity of summer diapause induced under different long daylengths (LD 14:10, LD 15:9, LD 16:8 and LD 17:7) was significantly different (the diapause duration ranged from 75 to 86 days at a constant temperature of 20 degrees C and from 76 to 88 days at a mean daily temperature of 19.0 degrees C). All results suggested that photoperiodic control of diapause induction and termination is significantly different between aestivation and hibernation.     

Nutritional and photoperiodic control of the seasonal reproductive cycle in Chrysopa mohave (Neuroptera)

Chrysopa mohave adults, which are predaceous, undergo a facultative reproductive diapause which can be induced, averted, and terminated in the laboratory by manipulating either photoperiod or diet. Photoperiods of LD 14:10 or shorter evoke a photoperiodically controlled diapause which breaks in long day (LD 16:8) conditions. Withholding prey induces the diapause syndrome in animals experiencing long day lengths, whereas supplying prey terminates this diapause; thus food constitutes a major factor in diapause induction and termination.Under short day regimens, with prey continuously present, diapause persists for approximately 60 days at 24±1°C; however, protein-fed, short day animals retain the diapause characteristics until they receive prey.Our experimental results in combination with field observations and examination of collected specimens, indicate four periods in the annual reproductive cycle as follows. The animals reproduce during April, May, and June when photoperiods are long and prey abundant. When prey become scarce during the dry months of the California summer, part of the population enters a food mediated diapause. During October, November, and December a short day diapause occurs in the population. Although the photoperiodic maintenance of diapause probably ends during early winter, the insects retain the diapause symptoms until prey becomes abundant at the end of March.     

Effect of photoperiod and temperature on diapause in a Florida strain of the tropical warehouse moth Ephestia cautella

A photoperiodically-controlled diapause of the long-day, short-day type was identified in a brown-winged, yellow-eyed strain of Ephestia cautella (Walker). The proportion of larvae diapausing in very long photoperiods was less than in short photoperiods. The mean critical photoperiod, here defined as that photoperiod giving half the maximum percentage of insects that diapause in response to photoperiod at a given temperature, was between 12 and 13 hr for the long-day reaction at both 20 and 25°C. The principal sensitive phase occurred near the time of the last larval moult. The mean duration of diapause was 2–3 months at 20°C and slightly longer at 25°C. The optimum temperature for diapause development was near 15°C, all larvae pupating within 24 days after a 45-day exposure at this temperature. Diapause could be terminated whenever larvae diapausing at 20°C were exposed to as few as five long (15 hr) photoperiods at 25°C. Long photoperiods at 20°C, or short photoperiods (9 hr) at 25°C were less effective in terminating diapause.     

Diapause induction and termination in the predatory mite Euseius finlandicus in peach orchards in northern Greece

The course of diapause induction as well as of diapause termination infemales of the predatory mite Euseius (Amblyseius)finlandicus Oudemans (Acari: Phytoseiidae) in Northern Greece wasdetermined by transferring females during winter and early spring from peachtrees to a short day (LD 8:16) or a long day (LD 16:8) photoperiod both at 20°C. The first diapause females were found in mid September andby the first week of October all the females were in diapause. The mean numberof days required for diapause termination under the short day photoperiod LD8:16 was gradually reduced from 93.7 days in the beginning of October to lessthan 20 days in mid February and early March. Under the long day photoperiod ofLD 16:8 diapause was terminated in less than 20 days irrespective of the dateof collection. These results indicate that by mid February photoperiodicsensitivity of females was lost and diapause was terminated. However, femaleswere found in their overwintering sites until the second half of March,probablybecause of the prevailing relatively low temperatures and lack of adequatefood.     

Photoperiodic control of larval development in the semivoltine cockroachPeriplaneta japonica (Blattidae: Dictyoptera)

Periplaneta japonica is semivoltine, entering early diapause in any (except the first) larval instar before the last, and late diapause in the last instar. Early diapause was induced under a short day of 13 h or less at 28°C, and under both short and long daylength (12–16 h) at 20°C. The shorter the daylength and the lower the temperature, the younger the instar was entering early diapause. Early diapause was terminated by a long day (16 h) or a high temperature (28°C), after which larvae grew faster in short days than in long days until the last instar, when they again entered diapause, always in short days and frequently in long days. This late diapause was terminated also by an increase in daylength and was always followed by adult emergence. In this case, 13 and 14 h daylengths after exposure to 12 h daylength were as effective as 16 h daylength. Ourdoor samples collected in late autumn, winter and early spring at Hirosaki (40.5°N) comprised two distinct size groups, corresponding with the early and late diapause instars. Based on these results, the seasonal development strategy and intriguing aspects of the photoperiodic response in this cockroach are discussed.     

Seasonal regulation of dormancy in Chrysopa carnea (Neuroptera)

In Ithaca, New York, diapause incidence in Chrysopa carnea exceeds 50 per cent among adults emerging between 31 August and 3 September. Apparently, decreasing late summer day lengths, which exceed the stationary critical photoperiod in the laboratory, act on the sensitive stages and induce diapause. Full diapause intensity occurs about 2 weeks after adult emergence; complete winter coloration appears approximately 2 weeks later. Photoperiodic stimili in combination with the geographic strain largely determine diapause depth.Decreasing autumn day lengths decelerate diapause development and maintain diapause until the winter solstice. Subsequently, short day lengths and cold temperatures slow diapause development. In nature, neither long days, increasing day lengths, nor chilling hasten diapause termination. Diapause duration is largely determined by the interaction between inducing photoperiod, maintaining photoperiodic and thermal stimuli, and geographic strain. In Ithaca, diapause ends (all response to photoperiod ceases) between 22 January and 12 March.After diapause ends, the animals retain their diapause characteristics until temperatures exceed 4°C. Post-diapause reproductive development in females requires approximately 100 heat units above 4°C; however, below 8°C mating and oviposition are absent. Although the winter coloration remains, mating occurs within 1 day after transfer from 4 to 24°C. Temperature determines the rate at which the green summer colour returns.     

Induction and termination of diapause inOrius predatory bugs

Photoperiodic induction of reproductive diapause at 18°C was investigated in fourOrius [Heteroptera: Anthocoridae] species.Orius insidiosus (Say) displayed a long-day response with a critical photoperiod between L11:D13 and L12:D12. Diapause in this species was terminated rapidly when the temperature and/or the daylength were increased.Orius majusculus (Reuter) also displayed a long-day response. The critical photoperiod fell between L14:D10 and L16:D8. Diapause in this species was not terminated within 14 days when both temperature and daylength were increased. InOrius albidipennis (Reuter) no diapause could be induced at photoperiods varying from L8:D16 to L16:D8. InOrius tristicolor (White) a high proportion of diapause was found at all photoperiods tested. The effect of temperature on photoperiodic induction of diapause was studied inO. insidiosus at L10:D14. Diapause occurred at 18°C, 21°C and 25°C, but not at 30°C. Again, diapause was terminated rapidly after transfer to 25°C/L16:D8. Exposing only the nymphal instars 1–5 to short daylength was not enough to induce diapause in the whole population ofO. majusculus. Orius predatory bugs are used as biocontrol agents against western flower thrips,Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidael, in greenhouses. The consequences of photoperiodic induction of diapause for the success of early season releases ofOrius are discussed.     

Summer diapause and nymphal growth in a subtropical cockroach: response to changing photoperiod

Abstract.  The effects of photoperiod on nymphal growth and adult reproduction were investigated in a small cockroach, Margattea satsumana, living on the subtropical, Hachijo island (33°N), Japan. Nymphal development is slow under constant photoperiods at 25 °C. The shortest mean duration of nymphal development (176 days) is observed at LD 14 : 10 h, followed by LD 12 : 12 h (221 days) and LD 16 : 8 h (309 days). Nymphal development is further prolonged when the nymphs are transferred from LD 12 : 12 to LD 16 : 8 h at 90 days after hatching. However, rapid and synchronized development is observed when nymphs were transferred in the opposite direction. A decreased change in photoperiod from LD 14 : 10 to LD 12 : 12 h also reduces the duration of nymphal development, and this cannot be explained by the results obtained at constant photoperiods. Similarly, nymphs reared at LD 16 : 8 h during the first 60 days mature more rapidly when transferred to LD 12 : 12 h than when transferred to LD 14 : 10 h. The developmental suppression induced by long days may represent a form of summer diapause that is terminated rapidly by short days. Based on these observations and field-census data, it is suggested that this cockroach has a univoltine life cycle overwintering as nondiapause adults, and that this life cycle is stabilized by the response to changing photoperiod.     

The role of photoperiod and temperature in determination of summer and winter diapause in the cabbage beetle,Colaphellus bowringi (Coleoptera: Chrysomelidae)

The cabbage beetle, Colaphellus bowringi, is a short-day species undergoing an imaginal summer and winter diapause. Its photoperiodic response highly depends on temperature. All adults entered diapause at ≤ 20 °C regardless of photoperiods. High temperatures strongly weakened the diapause-inducing effects of long daylengths. The diapause-averting influence of short daylengths was expressed only at high temperatures (above 20 °C). This indicates that the beetle has a cryptic ability to reproduce in summer. In fact, summer and winter diapause were induced principally by relatively low temperatures in the field, whereas photoperiod had less influence on diapause induction. The critical daylength for the autumnal population was between 12 h and 13 h. By transferring from a long day to a short day or vice versa at different times after hatching, it was shown that the sensitive stage with regard to photoperiod was the larva, whereas a long day was photoperiodically more potent than a short day. The sensitive stage to temperature encompassed the larval, pupal and adult stages. This different response pattern serves to ensure that the beetle enters summer and winter diapause in time. The selections for non-diapause trait under laboratory (at 25 °C) and natural conditions (at >24 °C) showed that the beetle could lose its sensitivity to photoperiod very rapidly.     

Photoperiodic Control of Pre-Adult Development and Adult Diapause Induction in Zoophytophagous Bug Dicyphus errans (Wolff) (Heteroptera,Miridae)

Zoophytophagous plant bugs (Heteroptera, Miridae) increasingly attract interest as agents of biological plant protection. In the laboratory experiment, the effects of the day length and temperature on the duration of the pre-adult period and on induction of facultative winter adult diapause were studied in Dicyphus errans (Wolff, 1804) collected in Italy. The experiment demonstrated that at 20°C the duration of the pre-adult period of D. errans significantly depended on the day length. On average, females developed 1.3 days longer than males and, at the same time, the day length equally influenced the duration of the pre-adult period in both sexes. The pre-adult period was the shortest under short-day conditions (10 to 12 h of light per day), reached its maximum at day length of 14 h, but then decreased at 15 h, and at day length of 16 h it was as short as under short-day conditions. Also, a pronounced long-day type photoperiodic response of adult diapause induction was recorded in females of D. errans at 20°C: under short-day conditions (10 to 14 h of light per day) almost all females entered diapause, whereas under long-day conditions (15 and 16 h of light per day) about 90% of females were mature. The threshold of this photoperiodic response was close to 14 h 30 min. The mean (± S.D.) egg load of mature females was 6.3 ± 4.0 eggs per female and did not depend on the day length at which the female was reared before and after the final molt. When photoperiodic response of adult diapause induction was observed at two constant temperatures (20 and 25°C), the proportion of mature females depended significantly on the day length but not on the temperature: the shapes of the photoperiodic response curves of diapause induction were almost the same within the near-threshold zone at 20 and 25°C, i.e., the photoperiodic response was thermostable. The set of two photoperiodic responses manifested at different stages of the species’ life cycle has an obvious adaptive significance. In Central Europe, D. errans has 2 or 3 generations per year and hibernates at the adult stage. Due to the thermostable photoperiodic response, females enter diapause always at the same time at the end of summer, regardless of the weather conditions of a particular year. When oviposition and pre-adult development are extended over a prolonged period in summer, nymphs from the later eggs might not be able to molt to adults in due time and then fully prepare for stable winter diapause. Under such circumstances, the photoperiodic response controlling the rates of pre-adult development acquires apparent adaptive meaning: with an autumnal shortening of the day length to 10–12 h, even under conditions of seasonal decrease in temperature, the rates of nymphal development increase and, thus, the chances of nymphs from the later eggs to molt to adults and properly prepare for overwintering also increase. The new data should be taken into account when analyzing the seasonal cycle of D. errans and developing the programs of mass rearing of this zoophytophagous mirid as an agent of biological plant protection.

     

Effect of photoperiod on winter and summer diapause of the soybean pod borer Leguminivora glycinivorella (Lepidoptera: Tortricidae)

To understand the geographical differences between diapause systems and synchronization of adult occurrence in the soybean pod borer Leguminivora glycinivorella (Lepidoptera: Tortricidae), we examined the timing of winter diapause termination and intensity of summer diapause using univoltine and potentially bivoltine individuals in Iwate, Japan. In laboratory rearing experiments of mature larvae maintained at constant temperature (20 °C), winter diapause intensity weakened by January without photoperiodic responses. Meanwhile, summer diapause was maintained by the long day length and presumably terminated with the photoperiodic transition from long to short day length. The intensity of summer diapause was stronger for cocoons that transitioned from a 16 h light to 8 h dark (LD 16:8) to a LD 15:9 photoperiod than for those that transitioned from LD 15:9 to LD 14:10. These results suggest that populations distributed in relatively low-latitude areas, with partly or potentially bivoltine individuals, would have a weaker summer diapause or none at all. Moreover, sexual differences in the number of days to emergence were not detected when individuals experienced a photoperiodic transition from long to short day length, suggesting that the summer diapause system may function to synchronize the emergence of males and females in the population examined.