Development, survivorship, and reproduction of Helicoverpa armigera (Lepidoptera: Noctuidae) under constant and alternating temperatures

Laboratory studies were conducted to assess the effect of temperature on the survival, development, fecundity, and longevity of Helicoverpa armigera (Hübner) at 11 constant temperatures ranging from 12.5 to 40 degrees C, as well as at five alternating temperature regimes (25-10, 30-15, 32.5-17.5, 35-20, and 35-27.5 degrees C) and under a photoperiod of 16:8 (L:D) h. H. armigera reared at constant temperatures did not develop from egg to adult (emergence) outside the temperature range of 17.5-32.5 degrees C. The alternating conditions expanded this range from 10 to 35 degrees C. The lowest developmental thresholds of the immature stages were estimated by a linear model and ranged from 10.17 (pupal stage) to 11.95 degrees C (egg stage) at constant temperature regimes and from 1.1 to 5.5 degrees C, respectively at alternating temperatures. The values of developmental thresholds estimated using the nonlinear (Lactin-2) model were lower than those estimated by the linear model for constant and alternating temperature regimes except for larval and pupal stages at constant temperatures. Mean adult longevity fluctuated from 34.4 d at 15 degrees C to 7.6 d at 35 degrees C. Females reared under all alternating temperature regimes laid more eggs than females reared at any, except the 25 degrees C, constant temperature treatment. The intrinsic rate of increase was highest at 27.5 degrees C, at both the constant and the corresponding alternating temperature regimes (0.147 and 0.139, respectively). Extreme temperatures had a negative effect on life table parameters.     

Effects of photoperiod and temperature on blood feeding,oögenesis and fat body development in the mosquito, Culiseta inornata

In the laboratory, blood feeding rates, oögenesis and fat body development were utilized to assess the effects of photoperiod and temperature in the conditioning of adult female Culiseta inornata for aestivation. Long-day (16L:8D) and short-day (8L:16D) photoperiods were examined in combination with temperatures of 15°C, 20°C, and 25°C. All tested individuals were reared from egg to adult under one of six possible regimes.Blood feeding occurred in approximately 60% of the females subjected to short-day conditions. Females subjected to long-day regimes exhibited gonotrophic concordance (the inhibition of blood feeding), evidenced by a decrease in overall blood-feeding rate to 20%. Inhibition of blood feeding by long-day females decreased in a linear fashion with increasing temperature. No interaction of the effects of photoperiod and temperature upon blood feeding was apparent. Examination of the ovarioles of post-blood feeding females, reared under each of the above conditions, revealed no evidence of gonotrophic dissociation (the inhibition of oögenesis despite continued blood feeding).Fat body hypertrophy occurred in females reared under long-day conditions, whereas hypotrophy of this tissue was apparent in short-day females. No significant difference in fat body development occurred between parous and nulliparous females reared under long-day photoperiod conditions. Short-day blood-fed females reared at 15°C deposited a significantly greater amount of fat than short-day blood fed females reared at 20° and 25°C, and short-day nonbloodfed females reared at 15°, 20°, and 25°C. The primary stimulus for fat body hypertrophy appears to be long-day photoperiod conditions. Temperature exerted little discernible effect upon this process, and there was no interaction between the effects of photoperiod and temperature upon the degree of fat body development.     

Temperature-related development of the parasitoid wasp Nasonia vitripennis as forensic indicator

Development times of the forensically significant parasitic wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) from oviposition to pupation, and from oviposition to adult emergence, were studied in the laboratory at temperatures of 15-35 degrees C using host pupae of the blowfly Protophormia terraenovae (Robineau-Desvoidy) (Diptera: Calliphoridae). Total developmental time of N. vitripennis from oviposition to adult emergence (mean+/-SD) was 43.5+/-2.4, 22.5+/-1.1, 14.8+/-1.7 and 11.3+/-0.9 days when reared at 15, 20, 25 and 30 degrees C, respectively. At 35 degrees C, N. vitripennis did not develop successfully. The rate of total immature development (1/days) increased with temperature. From linear regression of development rates, it was determined that the minimum threshold (tL) for total immature development was 9.8 degrees C (approximately 10 degrees C). Above this threshold, the overall thermal constant (K) for N. vitripennis was found to be 224.3+/-1.7 degree-days.     

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.     

Factors influencing the duration and termination of diapause in the Warehouse moth, Ephestia elutella

The influence of environmental factors on the duration of diapause was evaluated in larvae of Ephestia elutella (Hübner) reared in short photo-periods at 25C or below. Termination of diapause was hastened by long photoperiods, high temperatures, long periods at low temperature, or exposure to fumigants. Diapause terminated rapidly under long photoperiods at 30 or 25C, but not at 20C. The critical photoperiod for the termination of diapause was similar to that for induction, lying between 13 and 16 h at 25C. The longest duration of diapause occurred in constant darkness (DD) at 20C. However, batches of larvae reared at 20C in DD pupated a little sooner than batches reared under LD, if both were transferred at the start of diapause to warm, long-day conditions. Long exposure to low temperature reduced the number of long photoperiods necessary for the rapid termination of diapause at high temperature. Samples of larvae brought to the laboratory at monthly intervals from an unheated outbuilding in which they were overwintering, required an average of c. 200 days to pupate in DD at 25C when transferred in December, compared with only 32 days when transferred in February or March. By comparison, batches transferred to LD 16:8 at 25C required 39 days when transferred in December and 20–24 days in February and March. Holding at low temperature for long periods also encouraged synchronous emergence of the sexes. Duration of diapause was generally shorter in a laboratory stock than in a stock collected from the field.     

Short-day and low-temperature conditions promote reproductive maturation in the terrestrial slug, Lehmannia valentiana

Terrestrial slugs (Lehmannia valentiana) collected from a field in Osaka, southwestern Japan, were reared under long-day (16-h light and 8-h darkness, LD 16:8) or short-day conditions (LD 12:12) at 15, 20, or 25 degrees C for 60 days. Slugs reared under short-day conditions were heavier than those reared under long-day conditions; however, slugs reared at 15 degrees C gained more weight regardless of the photoperiodic condition. Gonads were significantly heavier under short-day conditions than under long-day conditions, and oogenesis and spermatogenesis were also induced under short-day conditions. Under short-day conditions, reproductive maturation was suppressed at 25 degrees C as compared with 15 and 20 degrees C, whereas under long-day conditions, lower temperatures induced reproductive maturation. In contrast, slugs reared under short-day conditions at 20 degrees C from the time of hatching gained more weight than those reared under long-day conditions at the same temperature. Moreover, short-day conditions induced reproductive maturation, similar to that observed in the field-collected slugs. In conclusion, short-day and low-temperature conditions promoted growth and reproductive maturation, whereas long-day and high-temperature conditions suppressed them in L. valentiana. Thus, L. valentiana reproduces from late autumn to spring in Osaka.     

The influence of temperature on the biology of triatominae. IX. Rhodnius nasutus Stal, 1859 (Hemiptera, Reduviidae)

The influence of temperature on the biology of Rhodnius nasutus Stal, 1859 (Hemiptera, Reduviidae) was studied in order to obtain a larger number of triatominae reared in laboratory to use in xenodiagnosis and to be able to get information for their proper control. The experiments were performed in two climatized chambers at 25 +/- 0.5 degrees C and 30 +/- 1 degrees C, 70 +/- 5% of relative humidity and photoperiod of 12 hours. Data in relation to evolution cycle, period between emergency of adults and first oviposition, fecundity, fertility, amount of blood ingested and fast resistance, are presented. The mean duration of the evolutive cycle for males and females was 145.7 days at 25 degrees C and 114.2 days at 30 degrees C. The mean of blood ingested to complete the evolutive cycle was 304.3 mg and 350.3 mg, at 25 degrees C and 30 degrees C, respectively. The triatominae survival on conditions of absolute fast was significantly higher at 25 degrees C than at 30 degrees C (P less than 0.01).     

Reproductive activity of Coelomera lanio (Coleoptera: Chrysomelidae)

The Cecropia spp. (Cecropiaceae) trees are attacked by several insects; among them, Coelomera lanio (Dalman) (Coleoptera: Chrysomelidae). The reproductive behavior of C. lanio was studied under laboratory conditions (12 hour photoperiod, 24.1 +/- 0.1 degrees C and mean relative humidity 67.7 +/- 0.6%), in Vi?osa, Minas Gerais, Brazil. The insects were reared in cages and in Petri dishes and fed leaves of Cecropia pachystachya Trec. Reproductive activity began 5.8 +/- 0.2 days after adult emergence and mean copulation time was 2.5 +/- 0.1 min. The female began oviposition only after 25.7 +/- 0.7 days. Each female laid a mean of 4.7 +/- 0.4 times (range 1-9). The mean number of eggs per oviposition and female was 129.2 +/- 2.4 and 587.4 +/- 92.1 respectively, and the time between egg-layings averaged 16.3 +/- 0.8 days.     

松毛虫狭颊寄蝇实验种群生态学研究

松毛虫狭颊寄蝇(Carcelia matsukarehae)是松毛虫重要的寄生天敌之一。在控制松毛虫自然种群增长中起重要的作用。本文在15℃、18℃、22℃、25℃、29℃、32℃6个恒温。相对湿度为70％～85％,光照为12：12(L：D)的条件下研究了松毛虫狭颊寄蝇的生态学特性。结果表明,松毛虫狭颊寄蝇的世代发育起点温度是5．23℃。积温为523．73日·度。成虫寿命在没有补充营养的条件下为1．3～8．06d,喂以30％蜜糖水。寿命可以从9．63d延长到36．42d。成虫产卵的最适温度为236℃,每雌最大产量为86粒．种群增长最适温度22～25℃．以近似方法计算22℃和25℃下实验种群繁殖特征生命表参数。在22℃,R0、T0、rc和A值分别为24．89、37．33、0．086和1．089。在25℃时分别为20．01、32．38、0．09和1．10．22℃时种群最大LxMx出现在成虫羽化后第33～38天。25℃时的LxMx最大值出现在成虫羽化后第29～34天。     

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.     

Parasitism, development and adult longevity of the egg parasitoid Telenomus nawai (Hymenoptera: Scelionidae) on the eggs of Spodoptera litura (Lepidoptera: Noctuidae)

When Telenomus nawai Ashmead or Trichogramma ostriniae Pang & Chen (Hymenoptera: Trichogrammatidae) was inoculated into intact egg masses of Spodoptera litura (Fabricius) that were covered with a scale-hair layer, T. nawai emerged from 76% of the eggs, while emergence of T. ostriniae was from only 3% of the eggs. When the hair layer was removed before inoculation, the rate by the latter increased to 21%. These observations confirmed that the hair layer effectively protects S. litura egg masses from attack by T. ostriniae, and that T. nawai parasitism is more effective. In order to assess the feasibility of T. nawai as a biological control agent for S. litura, parasitism rate, development time and adult longevity were examined in the laboratory. Emergence of T. nawai was observed in more than 95% of 0- and 1-day-old separated eggs of S. litura, but the rate decreased to 60% and 0% for 2- and 3-day-old eggs, respectively. The emergence rates of T. nawai were near 95% for temperatures in a range from 25 degrees C to 35 degrees C, but decreased to 80% at 20 degrees C. No parasitoids emerged at 15 degrees C. The developmental periods decreased as temperature increased from 20 degrees C to 35 degrees C. The developmental threshold occurred at 13.7 degrees C and 13.9 degrees C, and the effective accumulative temperatures from egg to adult emergence were 149.3 and 147.1 degree-days for females and males, respectively. Mean longevity of the adult females decreased with increasing temperature; 87.0 days at 15 degrees C and 9.5 days at 35 degrees C. The feasibility of the use of T. nawai for controlling S. litura is discussed.     

Mobility of mass-reared diapaused and nondiapaused Cydia pomonella (Lepidoptera: Tortricidae): effect of different constant temperatures and lengths of cold storage

Desirable behavioral attributes in mass-reared insects should include the ability to perform favorably under the various environmental conditions they encounter upon release in the field. Insect quality also may be influenced by storage conditions and storage duration before field release. We studied the effects of three different constant ambient temperatures (15, 20, and 25 degrees C) and different lengths of adult cold storage (0, 24, 48, and 72 h at 2 degrees C) on the locomotor activity of adult Cydia pomonella (L.) mass reared through diapause or standard production protocols. Mobility was assessed in actographs housed in a climate controlled chamber; tests lasted 24 h. We found that adult mobility was significantly higher for both males and females at 25 and 20 degrees C than at 15 degrees C. There were no significant differences in mobility in moths reared through diapause or nondiapaused production protocols. In addition, temporal analysis of the data revealed a significant shift in the diel patterns of activity for both genders when adults were tested at the three different temperatures. Moths exposed to the lower temperature shifted their activity pattern from evening to mid-afternoon, which may be an adaptive behavior to take advantage of the expected warmest period of the day. Diapaused adults were significantly less mobile when stored in the cold (24, 48, or 72 h of storage at 2 degrees C) than were diapaused adults that did not experience cold storage (0 h). However, length of time in cold storage did not significantly influence the mobility of adult codling moths reared through standard production protocols.     

Induction of reproductive diapause in Habrobracon hebetor (Hymenoptera: Braconidae) when reared at different photoperiods at low temperatures

Development of the parasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) at low temperatures was determined to identify rearing conditions that might result in adults that were in reproductive diapause. Diapausing adults would be expected to survive cold storage longer than nondiapausing adults for use in biological control programs. Only a few eggs were found in the ovaries when H. hebetor females were reared during the immature stages at 17.5 and 20°C with a 16-h photoperiod, and the ovaries were poorly developed and contained no eggs when females were reared with a 10-h photoperiod in these low temperatures. Rearing H. hebetor at 17.5 and 20°C did not result in diapause of immature stages, but did appear to result in possible adult reproductive diapause when the immature stages were reared with a 10-h photoperiod. Females reared during the immature stages at 17.5°C with a10-h photoperiod lived longer and took longer to lay their first eggs and to lay 50% of their eggs than those females reared at 17.5°C with a16-h photoperiod. Females reared during the immature stages at 20°C with a10-h photoperiod took longer to lay their first eggs and to lay 50% of their eggs, and they had a lower respiration rate, than those females reared at 20°C with a16-h photoperiod. Females that were reared in conditions that appeared to induce reproductive diapause resumed oviposition and their respiration rate increased soon after being transferred to a higher temperature (27.5°C). Thus, females reared at a 10-h photoperiod at 17.5 and 20°C appear to enter reproductive diapause.     

Biology of Cerotoma arcuatus (Coleoptera: Chrysomelidae) and field validation of a laboratory model for temperature requirements

Cerotoma arcuatus Olivier is a polyphagous pest of legumes [soybean, Glycine max (L.); dry beans, Phaseolus vulgaris (L.); and cowpeas, Vigna unguiculata (L.)], all of which are considered important protein sources for humans and domestic animals. Studies on the biology and temperature requirements of C. arcuatus were made under laboratory and field (cage) conditions. In the laboratory, insects were reared on soybean plants in incubators held at 18, 20, 22, 25, 28, 30, or 32 degrees C, 70 +/- 10% RH, and a photoperiod of 14:10 (L:D) h. A degree-days (DD) model developed based on the incubator data were validated in the field based on air and soil temperatures. The duration of the egg, larva-to-adult, and egg-to-adult period was inversely correlated with the temperature within the range of 18-32 degrees C, with the highest viability found from 20 to 30 degrees C. The temperature threshold for development and the thermal constant for the egg phase and the larva-to-adult periods were 13.6 degrees C and 106.7 DD, 8.3 degrees C and 399.4 DD, and 10.7 degrees C and 489.0 DD, respectively. The DD model for the egg-to-adult period, calculated using constant temperatures in the laboratory, was found to be valid for populations of C. arcuatus in the field, based on the fluctuating air and soil temperatures, although air temperatures provided more precise predictions. These data provide support for the rational control of this pest through population predictions based on their temperature requirements.     

Larval diapause of Monochamus urussovi and photoperiodic effects on larval development in tree bolts

To determine the larval diapause and the effect of photoperiod on development in Monochamus urussovi (Coleoptera: Cerambycidae), larvae were reared on Abies sachalinensis and Picea jezoensis logs and bolts. Larvae stopped developing in the final instar at 25°C and 16L : 8D (16 h light and 8 h dark) whereas an exposure to 5°C in the dark (134 days) following acclimation at 12°C under natural daylength led to adult emergence. When larvae were reared under 8L : 16D or 16L : 8D at 25°C with an intervening period of chilling at 5°C in the dark (112 days), a photoperiod of 8L : 16D induced a shorter time required for adult emergence after being returned to 25°C, and smaller adult body size than 16L : 8D.     

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.     

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

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

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.     

Life cycle regulation in the heather psyllid Strophingia ericae : responses to temperature and photoperiod

Abstract .The response of overwintering nymphs of Strophingia ericae (Curtis) (Homoptera: Psylloidea) to long and short photoperiods over a range of temperatures was investigated to determine the interaction between these factors and winter development as a regulatory mechanism of their life cycle. Strophingia ericae was successfully reared from egg to adult in a long photoperiod (LD 18:6 h) at 10, 15 and 20°C on its host plant Calluna vulgaris. Although development time was longer at 10 than at 15 or 20°C (≈ 263 days compared with ≈ 155 and ≈ 159 days, respectively), there was no interruption in development at any of these temperatures, indicating that there was no obligatory diapause. However, short photoperiod (LD 12:12 h) inhibited development of overwintering fifth instars collected from the field in early winter. Those collected in September and kept at 15°C developed to adult in ≈ 120 days in a short photoperiod (LD 12:12 h) compared with ≈ 40 days in a long photoperiod (LD 18:6 h). Inhibition became weaker in December and disappeared by January, when fifth instars developed to adult at the same rate in both long and short photoperiods (≈ 30 days). A similar photoperiodic response was observed when the experiment was repeated at 10°C, although development times were consistently longer. The observation that insects collected from the field in early winter were able to resume development immediately on transfer to favourable conditions (15°C and LD 18:6 h photocycle) suggests that there is a photoperiodically induced quiescence (rather than a true diapause) in overwintering S. ericae, which becomes progressively reduced as winter proceeds. It was concluded that the life cycle of the upland and possibly the lowland form of S. ericae is regulated by a winter-active photoperiodic inhibition of development, which effectively synchronizes the emergence of the adult stage with higher spring temperatures and renewed host plant growth.     

Developmental and reproductive biology of Scirtothrips perseae (Thysanoptera: Thripidae): a new avocado pest in California

The developmental and reproductive biology of a new avocado pest, Scirtothrips perseae Nakahara, was determined in the laboratory at five constant temperatures, 15, 20, 25, 27.5 and 30 degrees C. At 20 degrees C, S. perseae exhibited greatest larval to adult survivorship (41%), and mated females produced a greater proportion of female offspring at this temperature when compared to 15, 25, 27.5 and 30 degrees C. Average lifetime fecundity and preoviposition period was greatest at 15 degrees C at 39.6 eggs per female and 17.6 days, respectively. Jackknifed estimates of net reproduction (Ro), capacity for increase (rc), intrinsic rate of increase (rm), and finite rate of increase (lambda) were all significantly greater at 20 degrees C than corresponding values at 15, 25 and 27.5 degrees C. Population doubling time (Td) was significantly lower at 20 degrees C, indicating S. perseae populations can double 33-71% faster at this temperature in comparison to 15, 25 and 27.5 degrees C. Mean adult longevity decreased with increasing temperature, from a maximum of 52.4 days at 15 degrees C to a minimum of 2.4 days at 30 degrees C. Developmental rates increased linearly with increasing temperatures for eggs and rates were non-linear for development of first and second instar larvae, propupae, pupae, and for egg to adult development. Linear regression and fitting of the modified Logan model to developmental rate data for egg to adult development estimated that 344.8 day degrees were required above a minimum threshold of 6.9 degrees C to complete development. An upper developmental threshold was estimated at 37.6 degrees C with an optimal temperature of 30.5 degrees C for egg to adult development. Unmated females produced only male offspring confirming arrhenotoky in S. perseae.