Further studies on the involvement of the circadian system in photoperiodic control of antifreeze protein production in the beetle Dendroides canadensis

The role of circadian rhythmicity in the photoperiodic time measuring processes regulating antifreeze protein production in the beetle Dendroides canadensis was further investigated. Using “T” experiments larvae were exposed to environmental light cycle periods close to the period length of the endogenous circadian oscillator. The following light cycles were employed: light/dark 8/13, 8/14, 8/16, 8/18 and 8/19 corresponding to period lengths of 21, 22, 24, 26 and 27 h. Larvae maintained in cycles equal to or less than 24 h displayed a characteristic short-day response, showing significantly (P < 0.01) greater antifreeze protein activity than did those measured on the day of collection in late summer. In contrast, a long-day response was observed in larvae maintained under a 26- or 27-h light cycle in that antifreeze protein activity did not differ from that measured on the initial collection date.

The role of photoperiod and temperature in influencing the photoperiodic timing processes were examined with a series of resonance experiments. The first group consisted of a 24, 36, 48, 60 or 72-h light cycle, each with an 8-h photophase at temperatures of 20 or 17°C. Rhythmic increases in antifreeze protein levels at intervals of 24 h occurred under both temperatures. However, the lower temperature displaced the resonance curve in the vertical direction (i.e. increasing % population response) and reduced the difference between peaks and troughs on the resonance curve. Resonance experiments incorporating a 14-h photophase resulted in low antifreeze protein activity under all conditions except a 36-h light cycle in which a 67% induction was observed.

Eight hour resonance experiments were also conducted with D. canadensis collected in early spring to determine whether the circadian system participates in the photoperiodic timing processes influencing the spring termination of antifreeze protein production. Positive resonance results were obtained in that only larvae maintained in cycles of 36 and 60 h displayed significantly (P < 0.01) lower antifreeze activity when compared to animals on the initial collection date.

The combined results emphasize the involvement of the circadian system in the photoperiodic control of antifreeze protein production by D. canadensis during the fall and spring. Furthermore, the induction of antifreeze protein production is a function of light cycle and its waveform (photoperiod). Temperature appears to modify the photoperiodic response in some manner involving the photoperiodic time measuring processes. It is concluded that the photoperiodic response of antifreeze protein production by D. canadensis is dependent upon the entrainment of the circadian system by the light cycle.     

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 in Conogethes punctiferalis (Lepidoptera: Pyralidae)

The yellow peach moth, Conogethes punctiferalis (Guenée), a multivoltine species that overwinters as diapausing larvae, is one of the most serious insect pests on maize in China. Effect of photoperiod and temperature on larval diapause was examined under empirical laboratory conditions. Short‐day treatments caused larval diapause at 25°C, and the critical photoperiod was between 12 and 13 h (or 12 h 51 min) light per day. No sensitive instar was identified for diapause induction under alternated short‐ (L : D 11 : 13 h) and long‐day (L : D 14 : 10 h) treatments at different larval stages. However, accumulative treatment of three instars and 10 d under short‐day treatment was required for the induction of 50% larval diapause. All larvae entered diapause at 20°C, whereas less than 3% did so at 30°C, irrespective of the long‐ or short‐day treatment. Furthermore, under the short‐day treatment, more than 90% of larvae went into diapause with temperatures ≤ 25°C, but less than 17% did so at 28°C. In contrast, under the long‐day treatment, less than 19% of larvae went into diapause with temperatures ≥ 23°C. The forward shift (5°C) of critical temperature under the long‐day regime demonstrated the compensatory effect of temperature and photoperiod on diapause induction. In conclusion, C. punctiferalis had a temperature‐dependent type I photoperiodic diapause response; there was no sensitive instar for diapause determination, but the photoperiodic accumulation time countermeasures both of the short‐day cycles and the number of instars exposed, and the photoperiodic diapause response, was a temperature‐compensated phenomenon.     

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.     

Environmental and genetic control of the larval diapause of the Southwestern corn borer, Diatraea grandiosella

ABSTRACT. The interaction of photoperiod and temperature in the regulation of the induction and termination of the larval diapause of the Southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera), was examined. A population originating from south-eastern Missouri had critical daylengths for diapause induction of about 15h 5min (ecological threshold) and llh (physiological threshold). The ecological threshold was more stable than was the physiological threshold at temperatures lower than 25°C. Above 25°C the diapause response was suppressed. The insect appears to measure photoperiods in a stationary manner since a stepwise increase or decrease in photoperiod did not affect the incidence of diapause. In the critical region of the photoperiodic response curve, a higher incidence of diapause was found among females than among males. Females entered diapause later than did males, but resumed active development earlier than males. The rate of diapause development was more temperature dependent than was the rate of diapause induction, yet it was also clearly under photoperiodic control. The temperature coefficient (Q₁₀) for this process was about 4. Several other factors including sex-linkage, age, and geographic adaptations are involved in controlling the rate of diapause development, even more so than they are in controlling diapause induction. In the laboratory, the intensity of diapause declined gradually without larvae being exposed to non-diapause inducing conditions. Incubation of field-collected larvae revealed that their sensitivity to diapause maintaining photoperiods had ended by January. Three generations of selection of a Mississippi population of D. grandiosella at 30°C and LD 12:12 led to the production of an essentially diapause-free strain and a diapause strain.     

白蛾周氏啮小蜂滞育诱导及滞育后发育

本研究针对人工繁育白蛾周氏啮小蜂Chouioia cunea Yang过程中出现的小蜂滞育现象, 对其滞育诱导的光周期反应及敏感光照虫态进行了调查。结果表明: 沈阳地区的白蛾周氏啮小蜂属长日照型昆虫, 以老熟幼虫进入滞育状态, 但在不同的温度条件下诱导滞育的临界光周期不同, 在18℃时诱导滞育的临界光周期处于13L∶11D和14L∶10D之间; 在21℃和24℃时诱导滞育的临界光周期变短, 处于12L∶12D和13L∶11D之间。白蛾周氏啮小蜂滞育诱导的敏感光照虫态为幼虫期, 且以幼虫的后期最为敏感, 但整个幼虫期接受短光照对滞育的形成更为有利。通过观察白蛾周氏啮小蜂滞育后在18℃, 21℃, 24℃和30℃的恒温条件下的发育历期, 由最小二乘法计算出白蛾周氏啮小蜂老熟幼虫滞育后发育起点温度和有效积温分别为14.60±0.31℃和209.38±8.72日·度。这些结果可为进一步研究白蛾周氏啮小蜂的种蜂长期保存技术和指导商品蜂生产, 正确把握放蜂时机提供理论依据。     

Effect of photoperiod on the development and diapause of the green lacewing Chrysopa pallens (Neuroptera: Chrysopidae)

To investigate the physiology of Chrysopa pallens, the effect of photoperiod on diapause and development was examined in a Japanese population (33.4°N). The response stage for diapause of C. pallens was considered to be the prepupal stage. The critical photoperiod for diapause induction at 20.0°C was between 13 h light : 11 h dark (LD 13:11) and LD 14:10. The larval developmental period was affected by photoperiod: larvae in diapause took longer to complete their development. This difference of larval developmental period in relation to photoperiod was considered to be an adjustment of larval diapause timing.     

Photoperiodic responses of a northern and southern ecotype of black cottonwood

Photoperiod is an important signal controlling the onset of dormancy in perennial plants. Short days typically induce growth cessation, the initiation of cold acclimation, the formation of a terminal bud. bud dormancy and other adaptive responses. Photoperiodic ecotypes have evolved in many species with large latitudinal distributions. The photoperiodic responses of two northern (53°35′ and 53°50′N) and two southern (34°10′ and 40°32′N) genotypes of black cottonwood (Populus trichocarpa Torr. & Gray) were characterized by growing trees under a range of photoperiods in the greenhouse and growth chamber. Short days induced bud set in both ecotypes. resulting in trees with fewer leaves and less height growth than trees grown under long days. Short days also enhanced anthocyanin accumulation in the northern ecotype and decreased branching of the southernmost genotype. Two aspects of the photoperiodic response were evaluated for each trail: critical photoperiod. which was defined as the longest photoperiod that elicited a short-day response, and photoperiodic sensitivity, which was defined as the change in response per unit change in photoperiod. For each of the traits analyzed, the northern ecotype had a longer critical photoperiod and greater photoperiodic sensitivity than did the southern ecotype. The short critical photoperiod and reduced photoperiodic sensitivity of the southern ecotype resulted in a significant delay in bud set compared to that of the northern ecotype, even under a 9-h photoperiod. Typically, photoperiodic ecotypes have been characterized as having different critical photoperiods. Ecotypic differences in photoperiodic sensitivity, however, indicate that differences in the photoperiodic response curves cannot be completely described by the critical photoperiod alone. These results also suggest that the critical photoperiod. photoperiodic sensitivity and speed of bud set have a common physiological basis. Bud set occurred earlier hi the northern ecotype primarily because bud scale leaves were initiated earlier. For one of the northern genotypes, leaf primordia that were initialed under long days subsequently differentiated into bud scale leaves after the trees were transferred to a 9-h photoperiod. This demonstrates that primordia initiated under long days are not necessarily committed to becoming foliage leaves. The response to photoperiod did not differ appreciably between the greenhouse and growth chamber conditions that were tested.     

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.     

Effect of temperature on photoperiodic response in a selected 'non-diapause' strain of Pyrrhocoris apterus (Heteroptera)

Abstract. The artificially selected 'non-diapause' strain of Pyrrhocoris apterus (L.) (Heteroptera) showed no diapause response to photoperiod at 26°C (Socha & Hodkova, 1994). However, the diapause response to short-day photoperiod (LD 12:12 h) became apparent at lower temperatures of 17°C (70% diapause) or 20°C (41% diapause). Diapause was induced in 60% females by short-day photoperiod combined with thermoperiod of 26/16°C, whereas only 20% diapause was induced by the same thermoperiod under continuous darkness. Thus the time-measuring system was not removed by artificial selection but the diapause response was shifted to lower temperatures. The diapause response to short days seems to be favoured rather by low temperature during scotophase than by low temperature throughout the whole light/dark cycle. If the percentage of diapause at 26°C is compared in F₁ hybrids and in wild and selected parental strains the diapause appears to be dominant at LD 13:11 h but recessive at LD 11:13 h and LD 10:14 h. A hypothesis is proposed that the inheritance of the percentage of diapause in F1 hybrids is determined by interactions of genes controlling the temperature dependence of photoperiodic response.     

Maternal thermal and photoperiodic effects on the progeny diapause in Trichogramma telengai Sorokina (Hymenoptera: Trichogrammatidae)

Although maternal photoperiodic and maternal thermal effects on the progeny diapause have been demonstrated in a number of insect species, their interaction has been rarely studied. We investigated this interaction in Trichogramma telengai. In a series of experiments, maternal females were reared at day lengths of 12–18 h and at temperatures of 17, 20, 25 and 30°C. Their progeny developed under day length of 12 h and temperatures of 13, 14 and 15°C. The experiments showed that both short day and low temperature experienced by the maternal generation significantly increased the proportion of diapausing progeny. In particular, the threshold of the maternal photoperiodic response decreased with temperature. Under combinations of photoperiod with daily thermoperiod, the role of the “night” temperature in the induction of diapause in the progeny was much more important than that of the “day” temperature. We conclude that the interaction pattern between the photoperiodic and thermal maternal effects in T. telengai is generally the same as that between the photoperiodic and thermal responses directly influencing diapause induction in other long‐day insects. The threshold temperature of the maternal thermal response of T. telengai was about 25–27°C, while diapause can be induced if larvae develop at temperatures not higher than 15–16°C. This suggests that, at least in the studied Trichogramma species, the maternal thermal effect has no ecological value. In the practice of biocontrol, however, rearing of Trichogramma wasps at high temperature can drastically reduce the proportion of diapausing progeny.     

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.     

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.     

Responsiveness to photoperiodic changes in the circannual rhythm of the varied carpet beetle, <Emphasis Type="Italic">Anthrenus verbasci</Emphasis>

The circannual pupation rhythm of Anthrenus verbasci is entrained to an environmental cycle by changes in photoperiod. Exposure of larvae reared under short-day conditions to 4 weeks of long days can induce phase-dependent phase shifts. In the present study, we examined the range of photoperiodic changes effective for phase shifts at 20°C. For larvae under light/dark (LD) 12:12 conditions, 4-week exposure to LD 14:10 caused a clear phase delay, as great an extent as that brought about by exposure to LD 15:9 and LD 16:8. In contrast, the delay brought about by exposure to LD 13:9 was slight. For larvae under LD 10:14, exposure to LD 14:10 and LD 16:8 for 4 weeks induced a phase delay, but exposure to LD 12:12 did not. These results indicate that a clear phase delay is induced when the photoperiodic change exceeds a critical value in the photophase between 13 and 14 h, regardless of the amplitude of the change. Although phase advances were smaller than phase delays, they depended on the amplitude of photoperiodic changes rather than the absolute photophase duration in contrast to the case of the phase delay.     

Photo-thermal regulation of diapause in Trichogramma piceum Djur. (Hymenoptera, Trichogrammatidae)

Interaction of the photoperiodic conditions of development of maternal females (day lengths of 2 to 22 h at 20°C) with the thermal regime of development of their progeny (temperature of 12 to 15°C at day length of 12 h) in determination of prepupal diapause in Trichogramma piceum was studied under laboratory conditions. At 15°C the diapause was practically absent. At lower temperatures, the proportion of diapausing prepupae was maximal (25% of larvae at 14°C, 70% of larvae at 13°, and 80% of larvae at 12°C) if the maternal females developed under short day conditions (10–12 h). When maternal females developed at day lengths of 18–20 h, diapause was rarely recorded at all temperatures, while ultra-short (less than 8–10 h) days also caused a decrease in the proportion of diapausing progeny. The right (ecologically important) threshold of this maternal long-day photoperiodic response was about 14–15 h independently of the temperature during the progeny development. These results make it possible to clarify the mechanism of the “maternal photoperiodic correction of the progeny thermal response.” Although the impact of the maternal photoperiodic response can be revealed only within a very narrow thermal range, the relative strength of the diapause-inducing effect of different day lengths is independent of the temperature regimen of the progeny development.     

Diapause termination in two species of damselflies

Larvae of two species of damselflies, Enallagma hageni and E. aspersum, were collected in southwestern North Carolina and subjected to different combinations of daylength (SD, 11 hr day; LD, 14 hr day) and temperature to determine the factor critical in the termination of diapause. Diapausing larvae were collected in September, and 15 comparable groups of each species were given pretreatments (SD, 10°C; LD, 10°C; or SD, 21°C) for 2, 4, or 8 weeks and then transferred to SD, 21°C or LD, 21°C until emergence. Control groups were maintained under both photoperiods at 21°C.Response times (days from collection to emergence) for both species showed that rapid development required transfer to LD, 21°C regardless of the type of pretreatment or length of exposure. Larvae transferred to LD, 21°C after exposure to any of the three types of pretreatment for equal lengths of time developed at similar rates. Pretreatments at 10°C, which were equally effective with SD or LD, stimulated subsequent rapid development at LD, 21°C to a greater extent than continuous exposure to LD, 21°C conditions, and the longer the exposure to 10°C, the faster the subsequent response. Pretreatments at SD, 21°C also resulted in rapid development, similar to that of larvae exposed to 10°C, upon transfer to LD, 21°C conditions. Long daylengths administered only during pretreatments did not effect rapid development, since all larvae responded slowly when transferred to SD, 21°C. Diapause termination, therefore, was effected by LD, 21°C conditions preceded by exposure to either low temperatures, during which the photoperiod was not important, or short daylengths at 21°C.     

Environmental induction of larval diapause and life-history consequences of post-diapause development in the Large Copper butterfly,Lycaena dispar (Lepidoptera: Lycaenidae)

Many insects in temperate zones withstand the adverse conditions of winter through entering diapause and the two most important environmental stimuli that induce diapause are photoperiod and ambient temperature. The Large Copper butterfly, Lycaena dispar Haworth (Lepidoptera: Lycaenidae), is a Palearctic butterfly that hibernates as larvae. Since this butterfly is a near threatened species in some regions, there has been a growing need for a standardized protocol for mass rearing of this butterfly based on the adequate knowledge of its ecology. In the present study, we first identified that L. dispar larvae were sensitive to the photoperiodic induction of diapause during their first larval instar. We then investigated to what extent the diapause-inducing effects of photoperiod could be modified by ambient temperatures in L. dispar larvae by exposing them to the range of day-lengths (L:D 14:10, 12:12, 10:14 and 8:16) at three different temperatures (15, 20 and 25 °C). All larvae were induced to enter diapause at low ambient temperature (15 °C) regardless of photoperiod, whereas most of them (86 %) exhibited direct development when temperature was high (25 °C). The photoperiodic induction of diapause was evident when day-length was shorter than 14 h at intermediate temperature (20 °C). Pre-diapause development was prolonged at low temperatures. Finally, we found that post-diapause development of L. dispar larvae was determined by both the chilling temperature experienced by diapausing larvae and the duration of larval diapause. Adult emergence was enhanced when larvae were chilled at 8 °C and when they had been under the state of diapause for 20 days before they were treated to terminate diapause.     

Effects of temperature,photoperiod and soil humidity on induction of pseudopupal diapause in the bean blister beetle Epicauta gorhami

Larvae of the bean blister beetle Epicauta gorhami Marseul (Coleoptera: Meloidae) feed on grasshopper eggs in soil and undergo hypermetamorphosis. This beetle undergoes larval diapause in the fifth instar as a pseudopupa, a form characteristic of hypermetamorphosis in meloid beetles. The effects of temperature, photoperiod and soil humidity on larval development of E. gorhami are examined in a population in Miyazaki, Japan, using egg pods of Locusta migratoria L. as food. At lower temperatures (20 and 22.5 °C), all larvae become pseudopupae, regardless of the photoperiod. By contrast, at higher temperatures (27.5 and 30 °C), almost all larvae pupate at the end of the fourth instar, again regardless of the photoperiod. A long‐day photoperiodic response occurs only at an intermediate temperature (25 °C): under an LD 12 : 12 h photocycle, all larvae enter diapause, although the diapause incidence tends to decrease as the day length becomes longer. Pseudopupae are immobile and remain in diapause for ≥120 days when they are kept under the same conditions, except that diapause terminates within a relatively short time at 30 °C. Although lower soil humidity retards post‐feeding development, soil humidity has no effect on the diapause incidence. On the basis of the short developmental period and diapause avoidance under summer conditions, it is suggested that this beetle partially produces two generations a year in southwestern Japan.     

The regulation of development during diapause in Ephestia elutella (Hübner) by temperature and photoperiod

Diapausing larvae of Ephestia elutella reared at 20°C in short photoperiods (LD 11:13), and then maintained 12 weeks or longer at 5–15°C before transfer to 20 or 25°C, pupated sooner than unchilled controls. At 25°C, all samples kept in long photoperiods (LD 15:9) survived better and pupated faster than similarly treated samples held in short photoperiods (LD 9:15). Samples kept at 20°C after chilling pupated much slower than those at 25°C, and, except after exposure at 5°C, pupated at similar rates at LD 11:13 or 15:9, although mortality was higher at the shorter photoperiod. After exposure at 5°C, larvae required increased day-length as well as increased temperature to hasten pupation whereas after exposure at 10°C most responded to increased temperature only.For samples maintained in slightly heated or unheated outbuildings, the summer emergence was poorly synchronized and males on average emerged ahead of females. Samples moved from the unheated outbuilding to 25°C and long days in the laboratory in early spring, however, pupated quickly and males and females emerged together. A late phase of diapause development thus exists requiring both high temperature and long photoperiods to ensure a prompt resumption of morphogenesis. Spring temperatures in the United Kingdom are seldom high enough to synchronize the completion of diapause.     

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.