Effects of thermoperiods on diapause induction in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

Abstract. The effects of thermoperiods on diapause induction in continuous darkness or under a 12 : 12 h LD photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly, a typical short‐day species. The diapause response curves both at different constant temperatures and at the thermocycle of format CT x: (24 ? x) h (16 : 28 °C) under continuously dark rearing conditions showed that the incidence of diapause depended mainly on whether or not the mean temperature was ≤20 °C or >20 °C. If the mean temperature was ≤20 °C, all individuals entered diapause; if >20 °C, the incidence of diapause declined gradually with increasing mean temperatures. The thermocycle (CT 12 : 12 h) with a series of different cryophases (8–22 °C) and thermophases (24–32 °C) under continuous darkness demonstrated a cryophase response threshold temperature of approximately 19 °C and a thermophase response threshold temperature of approximately 31 °C. Thermoperiodic amplitude (temperature difference between cryophase and thermophase) was shown to have a significant influence on diapause induction at the mean temperatures of 22, 23 and 24 °C, but not at ≥25 °C. Thermoperiodic responses under LD 12 : 12 h clearly showed that the incidence of diapause was influenced strongly by the photophase temperature. The thermoperiod under LD 12 : 12 h induced a much lower incidence of diapause than the thermoperiod with the same temperature in continuous darkness. The ecological significance of thermoperiodic induction of diapause in this species is discussed.     

Thermoperiodic response and effect of photoperiod on thermoperiodic induction of diapause in Colaphellus bowringi

The effects of thermoperiods on diapause induction under continuous darkness (DD), continuous light (LL), and an L12:D12 photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), a short‐day species. Diapause could be induced by thermoperiod under both LL and DD; however, in the range of 24–30 °C, lower incidences of diapause were observed under LL than under DD. The critical cryophase was found to be dependent on the mean temperature of the thermoperiod applied. Although the thermoperiodic response pattern was similar under LL and DD, the incidence of diapause was higher under LL when the duration of the cryophase did not exceed 12 h. In contrast, when the duration of the cryophase was longer than 12 h, the incidence of diapause under LL was lower or equal to that under DD. When a thermoperiod of 24 °C (cryophase) and 28 °C (thermophase) was applied, the incidence of diapause was higher under LL than under DD, regardless of the duration of the cryophase. Thermoperiodic responses under a photoperiod of L12:D12 and under DD further revealed that induction of diapause was strongly influenced by the photophase temperature. Moreover, the incidence of diapause was lower when the thermophase coincided with the photophase than when the cryophase coincided with the photophase.     

Thermoperiodic induction of larval diapause in the European corn borer, Ostrinia nubilalis

Thermoperiodic induction of larval diapause was shown to occur in the European corn borer, Ostrinia nubilalis (Hübner). Using continuous darkness and thermoperiods of the format XC:24-XT(15:30°C), incidence of diapause was shown to be dependent on phase durations, with a critical cryophase of about 9.5 hr. A thermoperiodic response threshold was demonstrated; it was found to be very close to 17.5°C. Thermoperiodic amplitude (temperature difference between cryophase and thermophase) was shown to have no influence on the induction of diapause, within a relatively broad range of physiological temperatures. Thermoperiodic induction of diapause was shown to be at least partially independent from the effects of temperature on larval developmental rates.     

Aspects of the induction of diapause in a laboratory strain of the mite Tetranychus urticae

Some diapause characteristics were studied in a strain of the spider mite. Tetranychus urticae. which had been reared on bean plants in the laboratory for over 15 yr. The diapause induction response curve was of the long-day type, showing a sharply defined critical daylength of 13 hr 50 min. In constant darkness no diapause induction occurred, but with a photoperiod of 1L:23D diapause incidence was already complete. A thermoperiod with a 5°C amplitude induced diapause in combination with a short-day photoperiod only when the low phase of the thermoperiod coincided with the scotophase. The same thermoperiod did not induce any diapause in constant darkness. The photoperiodic reaction of the laboratory strain used in these experiments appeared to remain constant over a very long period of time and to be independent of the diapause history of previous generations of mites.Although photoperiodic sensitivity was demonstrated during the whole postembryonic development, sensitivity was maximal at the end of the protonymphal instar and declined rapidly during the deutonymphal instar. Only 2 inductive cycles of 10L:14D were required to induce up to 62% diapause if the mites were kept in continuous darkness during the remainder of their development. Long days or continuous light could reverse the inductive effect of a sequence of short-day cycles previously applied to the mites.Light breaks of 1 hr duration applied at different times during the dark period of a 10L:14D photoperiod generated a sharp bimodal response curve with two discrete points of sensitivity to the light breaks at 10 hr after ‘dusk’ and 10 hr before ‘dawn’, thus showing a remarkable similarity with the results obtained in light break experiments with some species of insects.     

Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, from tropical and temperate regions

Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, obtained from south-central Mexico (19°N latitude) and southeast Missouri (37°N latitude) were compared. Day length and temperature were found to serve as environmental cues to programme the larval diapause of both populations, but different critical values were observed. The critical day length for diapause induction was about 13 hr light/day for Mexican larvae and about 15 hr light/day for Missouri larvae, and was relatively stable at 20 to 30°C. Mexican larvae displayed a less-intense diapause than did Missouri larvae. Some diapausing Mexican larvae maintained at 25 or 30°C pupated in about 15 days, regardless of the day length to which they were exposed. The rate of diapause development of Mexican larvae was high at day lengths between 14 hr and 16 hr, whereas that of Missouri larvae was accelerated at day lengths of 16 hr at 25 and 30°C. Diapause development of Mexican larvae was virtually unaffected by chilling at 10°C, whereas that of Missouri larvae continued at a low rate at 10°C. Selection of Mexican larvae for diapause showed that only four generations were needed to significantly increase the incidence of diapause.     

Diapause induction in Eotetranychus smithi (Acari: Tetranychidae): effect of average temperature,but not of thermoperiod

Facultative diapause of Eotetranychus smithi appears to occur at the egg stage and is induced by temperatures ≤17.5 °C, independent of photoperiod. However, the effect of thermoperiod on the induction of diapause remains unclear. To answer this question, we exposed female E. smithi to various thermoperiods under constant light conditions. First, we found that the deposition order of eggs affected the incidence of diapause: the first eggs (exclusively males) tended to avert diapause compared with the second and third eggs (most of them are females), possibly because of the sex of the eggs. Next, the incidence of diapause of the second eggs decreased with shortening of the cryophase, which was associated with an increase of the average temperature, and it showed clear long‐day‐type thermoperiodic response curves. However, this species does not sense the ratio of day (thermophase) to night (cryophase) of a given thermoperiod. Short thermoperiods did not increase the incidence of diapause, but rather precluded the entry into diapause. We detected no sign of the involvement of the circadian system in diapause induction in the thermoperiodic Nanda–Hamner protocol. We conclude that diapause induction of E. smithi does not involve the circadian system, and thus does not show thermoperiodism. Diapause induction under the various thermoperiodic conditions tested in the present study appears to be derived from the temperature itself. E. smithi is an exceptional species that relies on temperature alone to induce diapause.     

Diapause induction in the thrips predatorAmblyseius cucumeris [Acarina: phytoseiidae] under greenhouse conditions

The predatory miteAmblyseius cucumeris (Oudemans) is an important biological control agent for thrips in commercial greenhouses, but its effectiveness in fall and winter is limited by reproductive diapause induced under short day conditions. Influence of photoperiod and temperature on diapause induction was investigated to provide information for successful management of the predator. Under 8∶16 (L∶D) photoperiods and 22°C photophase temperatures, diapause incidence was inversely related to scotophase temperature, decreasing from 100% diapause at 15°C to no diapause at 21°C. In continuous darkness, diapause was induced by thermoperiods of 20∶10 and 22∶17 and 22∶17 but not 25∶15°C (T∶C) (8h thermophase). Critical daylength for inducing diapause under 22∶17°C (T∶C) was 12.45 h, which was consistent with the trend in diapause incidence in mites collected from an established greenhouse population September to November. MostA. cucumeris diapaused only when exposed to diapause inducing conditions throughout their juvenile development and none stopped laying eggs when transferred from nondiapause to diapause inducing conditions as adults. After 14 generations of genetic selection for a nondiapause strain, diapause incidence was 33.3%.      

Photoperiodic induction of the pupal diapause in the tobacco hornworm, Manduca sexta

A study was made of photoperiodic induction of the facultative pupal diapause in the tobacco hornworm, Manduca sexta, reared on artificial diet in the laboratory. The species entered a prolonged diapause when the egg and larval feeding stages were reared in daily photoperiods of 13·5 hr or less. Diapause was induced in all insects at photoperiods ranging from 1 to 13 hr, and part of the population entered diapause at only 15 to 30 min of light per day. Photoperiods of 14 hr or more and continous darkness prevented diapause. Duration of diapause varied with the inductive photoperiod in which the hornworms were reared during the sensitive period. Insects reared in longer diapause-inducing photoperiods within a range of 12 to 13·25 hr remained in diapause longer than those reared in shorter photoperiods. There was no difference in the rate of larval development of hornworms reared in diapause-inducing vs diapause-preventing photoperiods. Temperatures of 26 to 30°C were most favourable for the photoperiodic induction of diapause; at 21°C, the critical photoperiod and incidence of diapause were decreased. Diapause induction was suppressed by low (18°C) and higher (33°C) temperatures. The number of inductive 12L:12D (light = 12 hr; dark = 12 hr) cycles required to induce diapause ranged from as few as 5 for some insects to as many as 12 for others when the post-inductive régimen was continuous light, but with insects previously held in continuous dark, as few as 2 12L:12D cycles during the last 2 days of larval feeding induced diapause in 38 per cent of the population. Only 3 to 4 cycles of 15L:9D during the final larval instar reversed inductive effects of 14 to 15 12L:12D cycles. Photoperiodic sensitivity extended from the late embryo to the end of larval feeding but showed considerable fluctuation during development with maximum sensitivity occurring just before egg hatch and during larval growth.Light breaks applied at different times during the dark period of 12L:12D cycles generated different response curves, depending on the number of cycles in which light breaks were repeated. When repeated for 6 cycles, a unimodal response curve was obtained; 10 cycles produced a bimodal curve and light breaks given for 18 cycles throughout the sensitive period averted diapause regardless of time of night applied. It is suggested that diapause is regulated by a photo- and thermolabile substance that accumulates during long nights (11 hr or more) and acts during the early pupal stage to inhibit the translocation and release of development-promoting neurosecretion from the brain.     

Insect photoperiodism: diversity of results in night-break experiments, including nonresponsiveness to light

Three night-break experiment protocols were utilized in an attempt to help clarify the role of the circadian system in photoperiodic time measurement in the European corn borer, Ostrinia nubilalis. Larvae raised in a light-dark (LD) cycle consisting of 12 hr of light alternating with 12 hr of darkness (LD 12:12), at a constant temperature of 30 degrees C, enter a state of arrested growth and development known as diapause (Takeda and Skopik, 1985). In the present research (Experiment 1), the induction of diapause was prevented by 1-hr light pulses that systematically scanned the dark phase of LD 12:12. Thus, the importance of 12 hr of uninterrupted darkness for maximal induction of diapause is stressed. The same experimental protocol applied to larvae already in diapause (Experiment 2), however, resulted in a bimodal curve of diapause termination. Although this result is consistent with the proposition that a nonperiodic hourglass timer underlies this event (Skopik and Takeda, 1986), it does not rule out the circadian system. Like LD 12:12, a thermoperiod in constant darkness (12 hr at 4 degrees C alternating with 12 hr at 25 degrees C) also induces diapause. Scanning such a thermoperiod with 1-hr light pulses, however, resulted in only a small effect (reduction of diapause) when light fell in the early to middle part of the warm phase (Experiment 3). Thus, the time-measuring system, under these experimental conditions, showed only a weak response to light. This unexpected result is discussed with respect to Experiment 1 and two general models that have been proposed to account for photoperiodic time measurement in insects.     

Diapause induction as an interplay between seasonal token stimuli,and modifying and directly limiting factors: hibernation in Chymomyza costata

Larvae of wild type (WT) strain of Chymomyza costata Zetterstedt (Diptera: Drosophilidae) enter diapause (stop developing) in response to short‐day signal at a constant 18 °C, whereas larvae of a non‐photoperiodic‐diapause (NPD) strain do not respond to photoperiodic signalling and continue in larval development irrespective of daylength. The present study shows that WT larvae also respond reliably to thermoperiodic signalling (daily cycles of temperature) under constant darkness, whereas the NPD larvae do not, suggesting that the pathways transducing the environmental token stimuli (photoperiod and thermoperiod) onto the diapause developmental programme might merge functionally in the central biological clock system known to be mutated in NPD strain. Temperature and larval population density modify the output of token stimuli signalling. High temperatures (>24 °C) tend to avert, whereas low temperatures (<18 °C), especially in combination with constant darkness, stimulate diapause induction in WT strain. Overcrowding (>200 larvae per 5 g of larval diet) lengthens the duration of larval development and induces a ‘diapause‐like’ developmental arrest of relatively weak intensity in up to 60% of larvae of both strains. At high temperatures (>30 °C), all WT larvae continue direct development but subsequently die during the pupal stage. Low temperature exposure (<12 °C) causes quiescence in the majority of the larvae of both strains. Starvation blocks development and causes mortality when applied in larvae younger than day 3 of the third instar. Older larvae survive starvation and their photoperiodically‐induced developmental pre‐programming is not affected. Collectively, the results show that diapause induction in C. costata is a result of various interacting effects of multiple environmental factors.     

Effect of temperature and photoperiod on the induction of diapause in the mite Metaseiulus occidentalis

Diapause in a predaceous mite, Metaseiulus occidentalis, from a Californian vineyard population is a photoperiodically induced, facultative, adult reproductive diapause in females. The laboratory-determined critical photophase at 19°C was estimated at 11·2 hr. At 16°C, the critical photophase under laboratory conditions was approximately 11·6 hr. Temperature influenced the photoresponse of M. occidentalis so that diapause was entirely averted at temperatures of 22, 25, and 30°C. Aestival diapause at higher temperatures and long photophases was lacking. Development was continuous under constant darkness at all the temperatures tested. Diapause termination in laboratory-reared mites occurred spontaneously under the inductive conditions. Under constant 19°C temperatures, females responded to photophases so that diapause was terminated most rapidly under a 16 hr photophase (in 18·6 days); the 12 and 8 hr photophases, at this temperature, were next in their effectiveness, with 27·9 and 73·0 days, respectively, required for termination.     

Effects of thermoperiods on the reproductive activity of females and on the maternal induction of larval diapause in the blowfly, <Emphasis Type="Italic">Calliphora vicina</Emphasis> R.-D. (Diptera,Calliphoridae)

The interaction of thermoperiod and photoperiod in their influence on the reproductive maturation of females and on the induction of the maternal effect determining larval diapause of the progeny of the blowfly, Calliphora vicina, was first investigated under laboratory conditions. Under the combination of a day length of 12 h with a thermoperiod (the alternation of 12 h long periods with temperatures of 10 and 20°C) the reproductive maturation of females was faster than at the corresponding mean constant temperature of 15°C. Under the “natural” thermoperiod, when the period with a temperature of 10°C coincided with “night-time” (the dark phase of the diurnal light-dark cycle) the maturation of females was slower than that under the “inverted” thermoperiod, when the period with a temperature of 10°C coincided with “day-time” (the light phase of the diurnal light-dark cycle). The proportion of diapausing individuals was maximal in the progeny of females kept at 20°C and decreased with the increase in temperature. Under thermoperiods (the alternations of 12 h long periods with temperatures of 20 and 26°C) the proportion of diapausing progeny was lower than that under the corresponding mean constant temperature of 23°C, but under the inverted thermoperiod with a high night temperature this effect was much stronger. In combination with the results of our previous studies, these data support the hypothesis that the effects of “night” and “day” temperatures are substantially different only when the thermal response interacts with a strong photoperiodic response.     

Photoperiodism in Ostrinia nubilalis: a new protocol for the analysis of the role of the circadian system

A 12-hr dark period, at a temperature high enough to permit time measurement to occur, is necessary for maximal induction of larval diapause in the European corn borer, Ostrinia nubilalis. In the present study, induction of diapause only occurred in a periodic environment. This was in the form of certain (1) light-dark (LD) cycles at a constant temperature; (2) thermoperiods in constant darkness (DD), but not constant illumination (LL); and (3) LD cycles with concurrent thermoperiods. A light-break experiment protocol, in which the pulses systematically scan the cold and warm phases of a thermoperiod in DD, is discussed as a way of helping clarify how seasonal time measurement is effected in Ostrinia.     

Effects of photoperiod and temperature on the development and diapause of the bark beetle Ips typographus

Abstract:  Diapause was induced in a Central European population of Ips typographus grown at 20°C when the day length decreased below 16 h [50% diapause incidence occurred in the 14.7:9.3 h L:D (light:dark) regime]. The non-diapausing adults fed on days 2–6 and 10–14 after the ecdysis and swarmed after the second feeding bout with chorionated eggs in the ovaries and sperm in the spermiducts. Neither gonads nor the flight muscles matured and no swarming occurred in the diapausing adults. The development from egg to adult took about 34 days in both 18:6 h (no diapause) and 12:12 h L:D (diapause) regimes, but it was extended by up to 30% without diapause induction when only larvae or pupae were exposed to L:D 12:12 h. Diapause was induced in insects reared at L:D 12:12 h through the last larval and the pupal instars and/or in the adult stage. Temperature ≥ 23°C prevented diapause induction at L:D 12:12 h but diapause occurred at L:D 14:10 h associated with 26:6°C thermoperiod. The effect of thermoperiods on the developmental rate requires further research. Exposure of the non-diapausing adults to 5°C for several days blocked feeding and evoked a diapause-like state, whereas diapausing adults fed and their gonads slowly developed at this temperature. Diapausing adults exposed in forest to low night temperatures and transferred in October to 20°C readily reproduced at 18:6, but not 12:12 h L:D photoperiods. After 2-months at 5°C and darkness, they became insensitive to the photoperiod, matured and most of them also swarmed at 20°C in the 12:12 h L:D regime. In a Scandinavian population, diapause occurred at 18:6 h L:D and was terminated either by exposure to 5°C or by very long photoperiod (L:D 20:4 h) combined with high temperature (23°C).     

Determination of effective light pulse and classical Bünsow experiment in the larval diapause of the Indian meal moth Plodia interpunctella

Plodia interpunctella Hübner (Lepidoptera: Pyralidae) comprises a model insect to analyse the photoperiodic time‐measuring system controlling its larval diapause. In the present study, the effective length of light pulse in night interruption experiments is determined at 25 °C. Various lengths of light pulse are tested by inserting them at the midnight of an LD 12 : 12 h photoperiod. When the light pulse is 15 or 30 min, the incidence of diapause is 86%. To inhibit the induction of diapause effectively, a light pulse of 1.75–2 h is needed. The incidence of diapause is 12% under an LD 12 : 5 : 2 : 5 h photoperiod. To determine the precise role of the light pulse, 2‐h light pulses placed at the midnight of an LD 12 : 12 h photoperiod are disrupted systematically by darkness. When a 2‐h light pulse is disrupted by 15 min of darkness, diapause is generally prevented (< 29%) regardless of the temporal position of darkness. Longer disruption by darkness induces diapause moderately (37–67%). A Bünsow experiment is also conducted at 25 and 20 °C, in which the main photophase of 12 h of light is combined with 24–72‐h scotophases scanned by a 2‐h light pulse. The photoperiodic cycle length tested, therefore, varies in the range 36–84 h. In each cycle length, the incidence of diapause fluctuates as the light pulse moves toward dawn. However, no regular and circadian changes in the percentage diapause are observed in relation to diapause determination.     

Photoperiodic induction of pupal diapause in Sarcophaga argyrostoma: Temperature effects on circadian resonance

Larval cultures of the flesh-fly Sarcophaga argyrostoma maintained in circadian ‘resonance’ experiments produced a high incidence of pupal diapause when the period of the light cycle was close to (T) 24, 48 or 72 hr, but a low incidence of diapause at T 36, 60 or 84 hr. Cultures pre-programmed for diapause by exposing pregnant females to long nights indicated the induction of non-diapause development at T 36, 60 and 84, whereas cultures pre-programmed for diapause-free development by exposing females to continuous light indicated the induction of diapause at T 24, 48 and 72.Raising the temperature reduced the heights of the diapause peaks whereas lowering the temperature raised them. With progeny from long-night-reared flies the lowest temperature tested (18°C) produced a result indistinguishable from an ‘hour-glass’ response, warning that ‘negative’ resonance experiments may merely indicate non-permissive conditions for demonstrating the involvement of circadian rhythmicity in insect photoperiodism.The results of the ‘resonance’ experiments and the effects of temperature are interpreted in terms of a multioscillator ‘external coincidence-photoperiodic counter’ model for the clock.     

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.     

Effects of background light conditions on thermoperiodic eclosion rhythm of onion fly Delia antiqua

To elucidate the effects of light on thermoperiodic regulation of adult eclosion rhythm in the onion fly, Delia antiqua, the responses to two thermoperiods, 29°C (12 h):21°C (12 h) and 25.5°C (12 h):24.5°C (12 h), with different amplitude and same average temperature, were examined in continuous darkness (DD) and continuous light (LL). Irrespective of the temperature step between warm phase (W) and cool phase (C), temperature cycles effectively entrained the adult eclosion rhythm in both DD and LL. Eclosion peaks, however, varied with light conditions and temperature step between W and C. It advanced by approximately 2–3 h in DD than in LL and at smaller temperature step. Background light conditions and temperature step also affect the amplitude of eclosion rhythm. It became lower in LL than in DD and at smaller temperature steps. On transfer to constant temperature (25°C), eclosion rhythm was elicited earliest in the pupae at 8°C temperature step in DD and latest in those at 1°C temperature step in LL. Pupae at 1°C temperature step in DD and at 8°C temperature step in LL demonstrated intermediate responses, but the eclosion rhythm was elicited 1 day earlier in the former than in the latter. This might be ascribed to the interaction between background light and temperature step under thermoperiodic conditions. The results suggest that continuous light and a smaller temperature step weaken the coupling strength between eclosion rhythm and thermoperiod, but the light effect is stronger than the temperature step effect.     

Diapause in the mite Metaseiulus occidentalis: Stages sensitive to photoperiodic induction

Stages of Metaseiulus occidentalis sensitive to photoperiod induction of diapause were determined by transferring various stadia into diapause-inducing conditions, and rearing them until adult females could be scored for reproductive condition. When eggs were transferred to 10 hr light at 19°C from 24 hr light at 25°C and the mites reared to adults, 92 per cent entered diapause. When larvae and all subsequent stages were kept under the inductive conditions, 62 per cent of adult females diapaused. Mites transferred as protonymphs into inductive conditions yielded only 10 per cent in diapause, and mites transferred as deutonymphs or newly emerged females did not enter diapause.However, adult females reared from eggs at 19°C under 12 hr light (which is near the critical photophase of 11·2 hr at 19°C) showed an unexpected sensitivity to photoperiod. Some newly emerged females oviposited upon transfer to an 8 hr photophase at 19°C. Some then stopped ovipositing and apparently entered diapause; these females resumed ovipositing after intervals ranging from 34 to 100 days. This was termed ‘switching’ into diapause. Some females reared under a 16 hr photophase at 19°C ‘switched’ also upon transfer as adults to shorter photophases—either 8 or 12 hr at 19°C. Thus, ‘switching’ may be due to transfer to shorter photophases. Promptness of mating vs delayed mating allowed ‘switching’ to be more easily detected.     

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.