Pupal diapause of Helicoverpa armigera (Lepidoptera: Noctuidae): sensitive stage for thermal induction in the Okayama (western Japan) population

Helicoverpa armigera (Hübner) exhibits a facultative pupal diapause, which depends on temperature and photoperiod. Pupal diapause is induced at 20 degrees C by short photoperiods and inhibited by long photoperiods during the larval stage. However, in some pupae (35% of males and 57% of females) of a non-selected field population from Okayama Prefecture (34.6 degrees N), diapause is not induced by short photoperiods. In the present experiment, the importance of temperature for diapause induction was studied in the non-diapausing strain, which was selected from such individuals reared at 20 degrees C under a short photoperiod of 10L:14D. Furthermore, the sensitive stage for thermal determination of pupal diapause was determined by transferring larvae of various instars and pupae between 20 degrees C and 15 degrees C. Diapause was induced by 15 degrees C without respect to photoperiod. When larvae or pupae reared from eggs at 20 degrees C under a short or a long photoperiod were transferred to 15 degrees C in the periods of the middle fifth instar to the first three days after pupation, the diapause induction rate was significantly reduced in both males and females, especially in females. In contrast, when larvae or pupae reared at 15 degrees C were transferred to 20 degrees C in the same periods, diapause was induced in males, but not in females. However, the diapause induction rate of pupae transferred to 20 degrees C on the fourth day after pupation was significantly increased in females. The results show that temperature is the major diapause cue in the photoperiod-insensitive strain and the periods of middle fifth larval instar to early pupal stage are the thermal sensitive stages for pupal diapause induction with some different responses to temperatures between males and females in H. armigera.     

Effects of photoperiod and low temperature on diapause termination in the yellow-spotted longicorn beetle (Psacothea hilaris)

Abstract. .The effects of photoperiod and low temperature on diapause termination in the yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe) (Coleoptera: Cerambycidae), were examined using a population from Ino, Japan. Diapausing insects obtained by rearing larvae under short daylength (12 or 13 h) at 25^oC were subjected to various treatments. When the photoperiod was changed at the same temperature, diapausing larvae showed a long-day response with a critical daylength between 13.5 and 14h. The diapause was terminated and consequently pupation occurred if the daylength was longer than 13.5 h. Chilling the diapausing larvae at 10^oC for 30 or more days also terminated diapause in most larvae irrespective of the photoperiods during and after chilling treatment. In contrast, the post-chilling photoperiod had a critical effect on development of diapausing larvae chilled for only 15 days.     

Role of photoperiod and temperature in the induction of overwintering pupal diapause in the spotted tentiform leafminer,Phyllonorycter blancardella

The role of photoperiod and temperature in the induction of overwintering diapause inPhyllonorycter blancardella (F.) (Lepidoptera: Gracillariidae) was examined in the laboratory and field using leafminers from commercial apple orchards in Ontario, Canada.P. blancardella exhibited a long-day response to photoperiod: long daylengths resulted in uninterrupted development whereas short daylengths induced diapause. The estimated critical photoperiod for diapause induction was L14.25∶D9.75. The larvae of leafminers destined to enter diapause took ca. 3× longer to complete development than the larvae of non-diapausing leafminers. The development prolonging effect of photoperiod decreased with decreasing daylength. Temperature modified the diapause inducing effect of photoperiod. At L14.25∶D9.75, diapause incidence was similar at 15 and 20°C but was lower at 25°C. Photoperiod also altered the normal relationship between development rate and temperature. At L14.25∶D9.75, the duration of larval development of diapausing leafminers was similar at 15, 20 and 25°C. Temperature alone is unlikely to have a role in the induction of diapause because leafminers exposed to natural late summer and fall temperature regimes and L16∶D8 did not enter diapause.     

The influence of physiological age of Argas reflexus larvae (Acari: Argasidae) and of temperature and photoperiod on induction and duration of diapause

The occurrence of diapause and quiescence was investigated in Argas reflexus engorged larvae, nymphs I and nymphs II. For diapause experiments, larvae were maintained at five different locations: at constant 20°C long day (LD; 17 h light:7 h dark) or short day (SD; 10 h light:14 h dark), at two locations with natural photoperiod and temperature and at one location with natural photoperiod but constant 15°C. At 20°C, diapause incidence was low in physiologically young larvae, increased with larval age, and then decreased to zero in specimens of increased physiological age. This pattern, observed both at constant LD and SD, suggests that the propensity to diapause changes with the physiological age of the unfed larva. The duration of diapause decreased with increasing larval physiological age at all locations, resulting in a seasonally synchronized moulting pattern. The results suggest that A. reflexus larvae are photoperiodically sensitive both before and after feeding and that decreasing daylengths may be particularly strong inductive stimuli. The developmental zero and thermal constant of the larvae were determined as 13.24°C and 220 degree-days, respectively. Degree-day measurements revealed that larval A. reflexus may enter a diapause of different length when fed between August and December and kept at natural daylength. Development of engorged nymphs I and nymphs II, but not of larvae, was ultimatively restricted at a temperature of 37.5°C, but immediately resumed at 25°C, demonstrating the occurrence of quiescence at high temperatures. Similarly, at a low temperature of 15°C, many nymphs I and II did not develop within 58 months, but did so successfully after transfer to 25°C, without additional food intake. Received: 20 May 1997 / Accepted: 4 August 1997     

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.     

Effect of different artificial diets on diapause induction under controlled temperature and photoperiod in the silkworm, Bombyx mori L.

ABSTRACT. Embryonic diapause of the silkworm, Bombyx mori , is generally induced by temperature and photoperiod during the egg stage of the previous generation and not in the larval stage. However, when silkworm larvae are reared on an artificial diet instead of mulberry leaves, their diapause is strongly affected by temperature and photoperiod experienced in the larval stage, with a distinct long-day response for diapause induction. Moreover when larvae which have been reared on artificial diet under long-day condition are fed mulberry leaves even for a short period of time, most of the resultant female adults lay diapause eggs. These results suggest that the photoperiodic response of larvae for diapause induction may be strongly suppressed by some components in mulberry leaves.     

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。     

Influence of photoperiod and temperature on reproductive mode in the Brine shrimp, Artemia franciscana

Brine shrimp, Artemia, exhibit two modes of reproduction: oviparity (diapause cyst production) and ovoviviparity (live larvae release). Environmental conditions determining these developmental routes are poorly understood, so we investigated the effects of photoperiod and temperature on reproductive mode. Nauplii of A. franciscana were hatched from cysts produced in the Great Salt Lake, Utah, and raised in 2% natural sea salt water under photoperiods of 24, 14, 12, or 10 h at 28 degrees or 20 degrees C. Mating pairs of mature shrimp were isolated and reared continuously under those conditions. The mode of reproduction shown by each pair was determined daily throughout their life span, and found to be greatly affected by photoperiod, and less influenced by temperature. The relative degree of oviparity increased as the photoperiod became shorter at both temperatures. In contrast, the degree of ovoviviparity was higher as the photoperiod became longer at both temperatures. The critical photoperiod appears to be between 12 and 14 h. For all photoperiods examined, the degree of oviparity was higher at 28 degrees C than at 20 degrees C, whereas the degree of ovoviviparity was greater at 20 degrees C than at 28 degrees C.     

Effects of constant and changing temperature conditions on diapause induction in Helicoverpa armigera (Lepidoptera: Noctuidae)

The effects of photoperiod and temperature on the induction and termination of facultative pupal diapause in Helicoverpa armigera (Lepidoptera: Noctuidae) were investigated under laboratory conditions. Exposing H. armigera larvae to both constant and fluctuating temperature regimes with a mean of 25°C and 20°C resulted in a type-III photoperiodic response curve of a short-long day insect. The long-day critical daylengths for diapause induction were ten hours and 12 hours at the constant temperatures of 25°C and 20°C, respectively. Higher incidences of diapause and higher values both for the longer and the shorter critical photoperiods for diapause induction were observed at fluctuating regimes compared with the corresponding constant ones. At alternating temperatures, the incidence of diapause ranged from 4.2% to 33.3% and was determined by the temperature amplitude of the thermoperiod and by the interaction of cryophase or thermophase with the photoperiod. Helicoverpa armigera larvae seem to respond to photoperiodic stimuli at temperatures >15°C and <30°C; all insects entered diapause at a constant temperature of 15°C, whereas none did so at a constant temperature of 30°C under all the photoperiodic regimes examined. Although chilling was not a prerequisite for diapause termination, exposure of diapausing pupae to chilling conditions significantly accelerated diapause development and the time of adult emergence. Therefore, temperature may be the primary factor controlling the termination of diapause in H. armigera.     

Effects of cold storage on field and laboratory performance of Trichogramma carverae (Hymenoptera: Trichogrammatidae) and the response of three Trichogramma spp. (T. carverae, T. nr. brassicae, and T. funiculatum) to cold

Delaying emergence of Trichogramma spp. is critical for commercial production. Here, diapause induction was considered for three species (Trichogramma nr. brassicae Bezdenko, Trichogramma carverae Oatman & Pinto, and Trichogramma funiculatum Carver), and the effect of storage temperature (4 degrees C, 8 degrees C, and 10 degrees C) and time (1-8 wk) was investigated for T. carverae. For all species, percentage of emergence was lowered after an initial diapause induction period (28 d at 14 degrees C and a photoperiod of 8:16 [L:D] h) and lowered further after 1-mo storage at 3 degrees C and a photoperiod of 0:24 (L:D) h. No wasps emerged after 2 mo of storage, suggesting that true diapause was not induced. The effect of 1-8-wk storage on wasp quality was investigated for T. carverae both in the laboratory and the field. Initial fieldwork suggested that this species could be successfully stored at 10 degrees C under continuous light (after 5-d development at 25 degrees C and a photoperiod of 16:8 [L:D] h) without reducing the ability of wasps to parasitize eggs in the field. In a second experiment, storage temperatures lower than 10 degrees C and storage times 3 wk or longer had a negative impact on emergence and longevity, and effects were not additive. Negative effects may partly reflect size changes, because size decreased in response to storage time, and there was an interaction between time and temperature effects on size. Storage time was the major factor influencing fecundity and field success; both fitness measures were reduced after storage of 3 wk or longer. T. carverae can therefore be successfully stored for up to 2 wk without detrimental effects, and 10 degrees C is the preferred storage temperature. T. carverae seems to survive unfavorable temperature conditions by entering a state of quiescence.     

Differential expression of two HSP70 transcripts in response to cold shock,thermoperiod, and adult diapause in the Colorado potato beetle

Partial clones for two members of Leptinotarsa decemlineata inducible 70kDa heat shock protein family (LdHSP70A and B) were developed using RT-PCR. LdHSP70A, but not LdHSP70B, was upregulated during adult diapause. The ability of L. decemlineata to express these two genes in response to subzero temperatures depended on the thermal history of the beetles. Chilling diapausing beetles increased the rate at which both LdHSP70A and B were expressed following a cold shock at -10 degrees C. Following cold shock at -10 degrees C, LdHSP70B expression peaked after 3h at 15 degrees C for chilled diapausing individuals, decreasing to near background levels by the sixth hour. In contrast, nonchilled diapausing beetles expressed their highest level of LdHSP70B only after 6h at 15 degrees C. Diapausing beetles exposed to a thermoperiod with a mean temperature of either 0 or -2.5 degrees C expressed significantly higher levels of both LdHSP70A and B than beetles exposed to constant 0 or -2.5 degrees C. These results demonstrate that the expression of LdHSP70A and B is differentially regulated in response to diapause and environmental conditioning.     

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.     

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.     

Induction and development of winter larval diapause in a drosophilid fly,Chymomyza costata

Photoperiodic response during induction of larval hibernal diapause of Chymomyza costata was characterized and the course of diapause development was analyzed in the laboratory. C. costata becomes sensitive to photoperiodic stimuli during an unspecified stage of its early development (embryo, 1st larval instar); the sensitivity gradually increases during the 2nd and early 3rd larval instars and reaches its maximum just before the moment when it abruptly ceases at the age of 15-19 days after oviposition. Diapause intensifies during a period of 2-3 weeks after induction and, later, is maintained without apparent development until death (between 150 and 250 days) under 18 degrees C and a short-day photoperiod (L10:D14, SD). Diapause may be terminated in a horotelic process by exposure to a low temperature (2 degrees C) during which larvae subsequently (1) synchronize their post-diapause development (requires up to 14 days of chilling), (2) lose photoperiodic sensitivity (2 months), and finally (3) terminate diapause (5 months). Alternatively, diapause may be terminated in a tachytelic process by exposure to a high temperature (18 degrees C) and long-day photoperiod (L16:D8, LD) during which no synchronization occurs and pupariation takes place after a mean of 25.2 days (with a broad range from 8 to more than 50 days). Larvae that are transferred from LD to SD during their sensitive period switch their developmental programming from pupariation to diapause. Proliferation of adult primordial structures (imaginal discs, neuroblasts) slows down within 1 day after transfer. In contrast, whole body growth continues for at least 3 days before its rate slows down and matches the rate characteristic for SD conditions.     

Factors governing the induction of diapause in Ephestia elutella and Plodia interpunctella (Lepidoptera)

Diapause in fully grown larvae of Ephestia elutella and Plodia inferpunctella was induced by low temperature and short photoperiods. Light intensities below 1 lx affected the induction of diapause in both species. At 20 and 25d?C, the critical photo-period for E.elutella was c. 14 h, and for P.interpunctella c. 13 h. The sensitive phase in both species occurred at about the time of the fourth larval moult. In E.elutella about seven short photoperiods were required for larvae to enter diapause. In P.interpunctella high population density during larval development increased the proportion of larvae entering diapause. The conditions inducing diapause in laboratory stocks, and in stocks collected from the field, were different. Laboratory stocks of both species did not enter diapause at 25d?C and required short photoperiods for diapause at 20d?C. Some larvae of the field stock of E.elutella entered diapause in constant darkness at 30d?C, the number being increased at low R.H., and almost all did in short photoperiods at 25°C. At 20T, most larvae of this stock entered diapause regardless of photoperiod, and at 15°C all did. In P.interpunctella up to one-third of larvae of the field stock entered diapause in short photoperiods at 25d?C, and all did if transferred to short photoperiods at 20d?C. In unheated premises, falling temperatures normally induce diapause in E.elutella each autumn, photoperiod only being important if temperatures are high. In P.interpunctella, photoperiod is a more important factor because it can override the effect of falling temperature to a greater extent than in E.elutella. In both species, however, different field populations may respond in different ways.     

Photoperiodic control of larval diapause in the yellow-spotted longicorn beetle, Psacothea hilaris: analysis by photoperiod manipulation

The photoperiodic control of diapause induction in the larvae of the yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe), was investigated using a west Japan-type population collected from Ino, Kochi Prefecture, Japan. In this population, the larvae expressed a long-day photoperiodic response with a critical daylength between 13.5 and 14 h at 25 °C ; under a long daylength, the larvae pupated after the 4th or 5th instar, while the larvae entered diapause under a short daylength after 2.3 additional molts on average. When the photoperiod was changed from a short (L12:D12) to a long (L15:D9) daylength, pupation occurred in most of the individuals irrespective of the time of the change. When the photoperiod was changed from long to short at 1 or 2 weeks after hatching, all of the larvae entered diapause, whereas when the photoperiod was changed at 5 weeks after hatching or later, most of the larvae pupated. The 2 weeks exposures to a long daylength against a 'background' of a short daylength at various times revealed that the larvae of this insect are most sensitive to the photoperiod from 4 to 6 weeks after hatching.     

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.     

Characteristics of summer diapause in the onion maggot,Delia antiqua (Diptera: Anthomyiidae)

Characteristics of summer diapause in the onion maggot, Delia antiqua, were clarified by laboratory experiments. Temperature was the primary factor for the induction of summer diapause in this species. The critical temperature for diapause induction was approximately 24 degrees C, regardless of the photoperiod. At 23 degrees C, the development of the diapausing pupae was arrested the day after pupariation, when about 7% of the total pupal development had occurred in terms of total effective temperature (degree-days). The most sensitive period for temperature with regard to diapause induction was estimated to be between pupariation and "pupation" (i.e., evagination of the head in cyclorrhaphous flies). Completion of diapause occurred at a wide range of temperatures (4-25 degrees C): The optimal temperature was approximately 16 degrees C, at which temperature only five days were required for diapause completion. The characteristics of summer diapause in D. antiqua are discussed in comparison with those of summer dormancy in a congener D. radicum and those of winter diapause in D. antiqua.     

Diapause induction in the oblique-banded leafroller Choristoneura rosaceana (Lepidoptera: Tortricidae): Role of photoperiod and temperature

Induction of diapause in the larval stage of the oblique-banded leafroller, Choristoneura rosaceana (Harris), was found to be dependent on both photoperiod and temperature. At constant temperatures of 24, 20 and 16°C, short photoperiods induced diapause. The critical photoperiod was between 14–15 h of light per day at 20 and 16°C. At 14 h light: 10 h dark, all larvae expressed diapause. Temperature had a modifying effect, and slightly shifted the larval response to diapause-inducing photoperiods. High constant temperatures of 28°C and above induced diapause in some individuals (< 20%), while fluctuating temperatures of 32 and 16°C in a 12-h cycle resulted in 67% diapause induction, suggesting that diapause could also be induced by fluctuating temperatures, particularly if the higher temperature exceeds 25°C.The first- and the second-instar larvae were the only two stages sensitive to diapause induction. Exposure of adult, egg and third, fourth, and fifth-larval instars to diapause-inducing conditions did not produce diapause. Although diapause was induced in the first or the second instars, it was always expressed in the third or fourth instar.     

Photoperiodism in the cabbage whitefly, Aleyrodes brassicae

ABSTRACT. Reproductive diapause was induced in A. brassicae by short photo-period at 15 and 20°C but was almost prevented at 25°C. The critical photoperiod was LD 153/4: 81/4 at 15°C, giving 60% diapause. Photoperiodic sensitivity was confined to the early immature stages. Food plant quality appeared not to influence the induction or prevention of diapause. Chilling facilitated diapause termination. Overwintering females brought into the laboratory as adults or pupae from the field from September to December took longer before laying their first eggs than females collected in January and February.