Survival of indianmeal moth and navel orangeworm (Lepidoptera: Pyralidae) at low temperatures

Concerns over insect resistance, regulatory action, and the needs of organic processors have generated renewed interest in developing nonchemical alternative postharvest treatments to fumigants used on dried fruits and nuts. Low-temperature storage has been identified as one alternative for the Indianmeal moth, Plodia interpunctella (Hiibner), and navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), common postharvest pests in California dried fruits and nuts. The response of eggs, nondiapausing larvae, and pupae of both species to exposure to low temperatures (0, 5, and 10 degrees C) was evaluated. Eggs of both species were the least tolerant of low temperatures. At 0 and 5 degrees C, pupae were most tolerant, but at 10 degrees C, nondiapausing larvae of both species were most tolerant, with lethal time (LT)95 values of 127 and 100 d for Indianmeal moth and navel orangeworm, respectively. The response of diapausing Indianmeal moth larvae to subfreezing temperatures also was evaluated. Diapausing larvae were very cold tolerant at -10 degrees C, with LT95 values of 20 and 17 d for long-term laboratory and recently isolated cultures, respectively. Diapausing larvae were far less tolerant at lower temperatures. At -15 degrees C, LT95 values for both cultures were <23 h, and at -20 degrees C, LT95 values were <7 h. Refrigeration temperatures of 0-5 degrees C should be useful in disinfesting product contaminated with nondiapausing insects, with storage times of 3 wk needed for adequate control. Relatively brief storage in commercial freezers, provided that the temperature throughout the product was below -15 degrees C for at least 48 h, also shows potential as a disinfestation treatment, and it is necessary when diapausing Indianmeal moth larvae are present.     

Effects of temperature and exposure time on mortality of stored-product insects exposed to low pressure.

The prospects of using low pressure that creates a low-oxygen atmosphere to control stored-product insects were investigated in the laboratory. Eggs, larvae, and pupae of Tribolium castaneum (Herbst), Plodia interpunctella (Hübner), and Rhyzopertha dominica (F.) were exposed to 32.5 mmHg in glass chambers at 25, 33, 37, and 40 degrees C for times ranging from 30 min to 144 h. Time-mortality data were subjected to probit analyses and lethal dose ratios were computed to determine differences in lethal time (LT) values among all species-life stage combinations across the four temperatures. Eggs of each species were the life stage most tolerant to low pressure. Pupae of T. castaneum and R. dominica were more tolerant to low pressure than larvae. In all life stages, mortality increased with increasing exposure time to low pressure and also with increasing temperature. Immature stages of R. dominica were more tolerant to low pressure than immature stages of the other two species. The LT99 for R. dominica eggs was 176.32 h at 25 degrees C and that for P. interpunctella eggs was 28.35 h at the same temperature. An increase in temperature to 33 degrees C resulted in a LT99 < of 85.98 h for R. dominica and 6.21 h for P. interpunctella. Higher temperatures resulted in further significant reduction in lethal time values. Low pressure represents a simple, nonchemical alternative to fumigants such as methyl bromide and phosphine for controlling pests of stored-products or other commodities.     

Cold hardiness of the fly pupal parasitoid Nasonia vitripennis is enhanced by its host Sarcophaga crassipalpis

Supercooling points (SCPs) and low temperature survival were determined for diapausing and nondiapausing larvae of the ectoparasitoid Nasonia vitripennis. Neither nondiapausing nor diapausing larvae could survive tissue freezing. The SCP profiles were nearly identical for nondiapause-destined (-27 degrees C) and diapausing larvae (-25 degrees C), but these values were not indicative of the lower limits of tolerance in either type of larvae: larvae were killed by chilling at temperatures well above the SCP. Diapausing larvae could withstand low temperature exposures 3-8 times longer than their nondiapausing counterparts. Low temperature survival was enhanced in diapausing and nondiapausing larvae by their encasement within the puparium of the host flesh fly, SARCOPHAGA CRASSIPALPIS: the LT(50)s determined for nondiapausing and diapausing larvae enclosed by fly puparia were 2-3 times higher than values calculated for larvae removed from the puparia. Additional low temperature protection was gained through acquisition of host cryoprotectants during larval feeding: nondiapausing parasitoid larvae that fed on diapausing flesh fly pupae with high levels of glycerol were able to survive exposure to a subzero temperature 4-9 times longer than wasps reared on nondiapausing fly pupae that contained lower quantities of glycerol. Alanine may also contribute to the cold hardiness of N. vitripennis, as evidenced by the fact that larvae feeding on diapausing fly pupae both contained higher concentrations of alanine and exhibited greater cold hardiness. The results thus demonstrate that several critical features of cold hardiness in the wasp are derived from biochemical and physical attributes of the host.     

Thermal death kinetics of fifth-instar Plodia interpunctella (Lepidoptera: Pyralidae)

Heat treatments have been suggested as alternatives to chemical fumigants for control of postharvest insects in dried fruits and nuts. Conventional forced hot air treatments heat product too slowly to be practical, but radio frequency treatments are capable of more rapid product heating. While developing radio frequency heat treatments for dried fruits and nuts, the heat tolerance of nondiapausing and diapausing fifth-instar larvae of the Indianmeal moth, Plodia interpunctella (Hübner), was determined using a heating block system developed by Washington State University. Both a 0.5th order kinetic model and a classical empirical model were used to estimate lethal exposure times for temperatures of 44-52 degrees C for nondiapausing fifth-instar larvae. We obtained 95% mortality at exposures suitable for practical radio frequency treatments (< or = 5 min) with temperatures of 50 and 52 degrees C. Diapausing larvae were significantly more tolerant than nondiapausing larvae at the lowest treatment temperature and shortest exposure, but differences were not significant at more extreme temperature-time combinations. Previous studies showed that fifth-instar larvae of the navel orangeworm, Amyelois transitella (Walker), were more heat tolerant than either diapausing or nondiapausing Indianmeal moth larvae. Consequently, efficacious treatments for navel orangeworm would also control Indianmeal moth.     

Upregulation of two actin genes and redistribution of actin during diapause and cold stress in the northern house mosquito, Culex pipiens

Two actin genes cloned from Culex pipiens L. are upregulated during adult diapause. Though actins 1 and 2 were expressed throughout diapause, both genes were most highly expressed early in diapause. These changes in gene expression were accompanied by a conspicuous redistribution of polymerized actin that was most pronounced in the midguts of diapausing mosquitoes that were exposed to low temperature. In nondiapausing mosquitoes reared at 25 degrees C and in diapausing mosquitoes reared at 18 degrees C, polymerized actin was clustered at high concentrations at the intersections of the muscle fibers that form the midgut musculature. When adults 7-10 days post-eclosion were exposed to low temperature (-5 degrees C for 12 h), the polymerized actin was evenly distributed along the muscle fibers in both nondiapausing and diapausing mosquitoes. Exposure of older adults (1 month post-eclosion) to low temperature (-5 degrees C for 12 h) elicited an even greater distribution of polymerized actin, an effect that was especially pronounced in diapausing mosquitoes. These changes in gene expression and actin distribution suggest a role for actins in enhancing survival of diapausing adults during the low temperatures of winter by fortification of the cytoskeleton.     

Cold hardiness adaptations of codling moth, cydia pomonella

The cold hardiness adaptations of natural and laboratory reared populations of the codling moth, Cydia pomonella, were examined. Hemolymph, gut, and whole body supercooling points (SCPs), 24-h LT50s, polyhydroxy alcohol concentrations, hemolymph freezing points, and hemolymph melting points were determined. Nondiapausing codling moth larvae do not have appreciable levels of ice nucleators in the hemolymph or gut. Whole body supercooling points were higher than hemolymph supercooling points. For nondiapausing larvae, LT50s were significantly higher than both the whole body and the hemolymph supercooling points, indicating the presence of chill sensitivity. As the larvae left the food source and spun a cocoon, both hemolymph and whole body SCPs decreased. Diapause destined larvae had significantly lower hemolymph SCPs than nondiapausing larvae, but whole body SCPs were not significantly different from nondiapausing larvae of the same age. The LT50s of diapause destined and diapausing larvae were significantly lower than that of nondiapausing larvae. Codling moths are freezing intolerant, with LT50s close to the average whole body supercooling point in diapause destined and diapausing larvae. The overwintering, diapausing larvae effectively supercool to avoid lethal freezing by removal of ice nucleators from the gut and body without appreciable increase of antifreeze agents such as polyols or antifreeze proteins.     

Cold hardiness of Helicoverpa zea (Lepidoptera: Noctuidae) pupae

An insect's cold hardiness affects its potential to overwinter and outbreak in different geographic regions. In this study, we characterized the response of Helicoverpa zea (Boddie) pupae to low temperatures by using controlled laboratory measurements of supercooling point (SCP), lower lethal temperature (LT(50)), and lower lethal time (LLTime). The impact of diapause, acclimation, and sex on the cold hardiness of the pupae also were evaluated. Sex did not significantly affect the SCP, LT(50), or LLTime. However, the mean SCP of diapausing pupae (-19.3°C) was significantly lower than nondiapausing pupae (-16.4°C). Acclimation of nondiapausing pupae to constant temperatures from 10 to 20°C before supercooling also produced a significantly lower SCP than nondiapausing pupae held at 25°C. The LT(50)s of nondiapausing and diapausing were not significantly different, but confirmed that H. zea pupae are chill-intolerant because these lethal temperatures are warmer than the corresponding mean SCPs. Diapausing pupae survived longer than nondiapausing pupae at the same, constant, cold temperatures, a finding consistent with the SCP results. Both of these results suggest enhanced cold hardiness in diapausing pupae. When laboratory results were compared with field temperatures and observed distributions of H. zea in the contiguous United States, the laboratory results corroborated what is currently perceived to be the northern overwintering limit of H. zea; approximately the 40(th) parallel. Moreover, our research showed that areas north of this limit are lethal to overwintering pupae not because of low temperature extremes, but rather the length of time spent at near-zero temperatures.     

Role of antioxidant defense during different stages of preadult life cycle in European corn borer (Ostrinia nubilalis, Hubn.): Diapause and metamorphosis

Antioxidant enzymes, total glutathione (GSH), and ascorbic acid (ASA) were determined in whole body homogenates of nondiapausing larvae, diapausing larvae during the diapausing period (October, December, and February), and in pupae emerged from both diapausing and nondiapausing larvae of the European corn borer (Ostrinia nubilalis, Hubn., Lepidoptera: Pyralidae). The activities of catalase, selenium nondependent glutathione peroxidase (GPx), and glutathione-S-transferase (GST), as well as the content of GSH and ASA, were found to vary throughout the larval diapause. Compared to diapausing larvae, nondiapausing larvae were higher in levels of catalase, GPx, GST, and dehydroascorbate reductase (DHAR) activity. GSH content was also increased. However, nondiapausing larvae contained less ASA than diapausing ones. Pupae had higher GPx and GST activity and an increased ASA content compared to larvae. The pupae emerged from nondiapausing larvae had higher GST, glutathione reductase (GR), and DHAR activities, but lower GPx activity and ASA content than those emerged from diapausing larvae. Correlation analysis revealed differences in the way the antioxidant level is equilibrated for a particular stage and developmental pattern. The results suggest that cellular antioxidants are involved in both the protection of cells and the regulation of redox levels during the pre-adult stages of Ostrinia nubilalis. Arch. Insect Biochem. Physiol. 55:79-89, 2004.     

The sensitivity of larval Plodia interpunctella and Ephestia elutella (Lepidoptera) to light during the photoperiodic induction of diapause

ABSTRACT. The incidence of diapause in larvae of Plodia interpunctella and Ephestia elutella held under two light systems was examined. Both systems progressively shortened the photophase of 24-h cycles, one with a motorized dimming switch providing dawns and dusks about 1 h long, the other switching the lights instantaneously. The mean critical photoperiod for P. interpunctella was about 131/4 h and for E. elutella just over 14 h. In both species light intensities as low as 0.2 lx influenced the induction of diapause. In P. interpunctella the critical photoperiod and sensitivity to light were similar at 23.±.;5°C and 20.5±0.5°C. At 22.5°C the percentage of diapausing larvae of E. elutella increased from 2% in long photoperiods (> 15 h light), to 100% in short photo-periods (t 12.5h light). Fox P. interpunctella , at 22.5°C the percentage increased from zero in long photoperiods (> 14 h light) to about 98% in short photoperiods (< 11.5h light), and at 20°C from 12% to 100% over a similar photoperiodic range. Similar results were obtained under selected fixed photoperiods, switched on or off instantaneously.     

Mortality of life stages of cowpea weevil (Coleoptera: Bruchidae) exposed to low pressure at different temperatures

Previous studies have shown that low pressure creates a low oxygen controlled atmosphere that can kill stored-product insects. The current study was conducted to determine the mortality of life stages of the cowpea weevil, Callosbruchus maculatus (F.) (Coleoptera: Bruchidae), exposed to different low pressures and temperatures for various exposure periods. The adults were the most susceptible life stage to low pressure; 99% mortality was achieved within 0.8 h at 32.5 mmHg, 30 degrees C. The pupae were the most tolerant life stage to low pressure, requiring exposure periods between 28.98 and 153.20 h at temperatures of 20-35 degrees C to achieve 99% mortality. Mortality increased with exposure time and also with increasing temperature in all life stages. Early stage eggs (3 h old) and late stage eggs (48 h old) experienced higher mortality (values for LT99 of 42.331 and 46.652 h, respectively) compared with intermediate aged eggs (24 h old; LT99 of 74.735 h) under the same conditions of low pressure and temperature. Dried beans, including cowpea, Vigna unguiculata (Walp.), are currently protected with fumigants. Application of low pressure as a pest management tool represents a potential nonchemical alternative to fumigants such as methyl bromide and phosphine for controlling the cowpea weevil and related bruchids.     

Age‐dependent changes in tolerance to cold and accumulation of cryoprotectants in overwintering and non‐overwintering larvae of European corn borer Ostrinia nubilalis

Abstract The age‐dependent cold hardiness profile of Ostrinia nubilalis is compared between nondiapausing and diapausing larvae, as well as with field‐collected larvae. The results suggest that both cold tolerance and accumulation of cryoprotectants depends upon the age of O. nubilalis larva. Late fifth‐instar nondiapausing larvae are more cold tolerant than younger fifth‐instars because they show enhanced ability to withstand sub‐zero temperatures. No appreciable difference is observed between the experimental groups of diapausing larvae as far as their supercooling ability and tolerance at sub‐zero temperatures above the supercooling point. In general, both field‐collected and diapausing larvae are more cold tolerant than nondiapausing larvae, indicating a direct link between diapause and cold hardiness. The age of diapausing larvae affects the ability to accumulate glycerol. Glycerol levels of 45‐day‐old diapausing larvae are significantly higher (2.7‐fold) compared with 90‐day‐old diapausing larvae. Moreover, diapausing larvae display a five‐ to 13‐fold higher glycerol content compared with nondiapausing larvae. There is a trend for an age‐dependent cold hardiness profile in O. nubilalis and further tests that could demonstrate a causal relationship between age and cold tolerance are needed.     

Geographical and diapause-related cold tolerance in the blow fly,Calliphora vicina

Three geographical strains of the blow fly, Calliphora vicina, were tested for cold tolerance at 0 degrees, -4 degrees and -8 degrees C. Survival to eclosion after 1 to 18 days of cold exposure was greater for diapause-destined larvae than for nondiapause-destined larvae of the two northern strains (Nallikari, Finland 65 degrees N and Edinburgh, Scotland 55 degrees N) but not for the southernmost strain (Barga, Italy 44 degrees N) where no clear differences were apparent. Diapause-destined larvae of the Edinburgh strain were more cold tolerant than those from Nallikari, at both -4 degrees and -8 degrees C, a difference possibly attributable to the long-lasting snow cover in the more northern locality, which might insulate the overwintering soil microclimate. At 0 degrees C, however, Nallikari larvae were more cold tolerant than Edinburgh or Barga. This was also the case for nondiapause-destined larvae, indicating that cold tolerance may occur, in part, independently of the diapause programme. In all three strains diapausing larvae were more cold tolerant than same-age (nondiapausing) pupae. For Nallikari, but not Barga, wandering larvae from short-day exposed flies, therefore initially programmed for diapause, but diverted from the diapause pathway by larval breeding at 19 degrees C, were significantly more cold tolerant than nondiapause larvae from long-day parents, indicating some maternal regulation of larval cold tolerance. There was, however, no evidence for an additional cold hardiness in larvae acclimatised to cold by a gradual reduction of temperature.     

Evaluation of thiamethoxam and imidacloprid as seed treatments to control European corn borer and Indianmeal moth (Lepidoptera: Pyralidae) larvae

Efficacy of thiamethoxam (Cruiser) and imidacloprid (Gaucho) were evaluated as seed treatments for controlling European corn borer, Ostrinia nubilalis (Hübner) and Indianmeal moth, Plodia interpunctella (Hübner) larvae in stored grain. At approximately 22-26 degrees C, all fifth instar European corn borers died after two or 4 d of exposure to corn treated with 250 and 500 ppm thiamethoxam, respectively, while mortality of larvae exposed for two and 4 d on corn treated with 6.3-937.5 ppm imidacloprid did not exceed 48% at any concentration. At 29 degrees C, all nondiapausing fifth instars were killed after 3, 4, and 6-d exposure to 400, 300 and 200-ppm thiamethoxam, respectively, while survival increased at successively lower concentrations of 100, 50, 25, and 12.5 ppm. At 29 degrees C, the LC50 decreased from 85.9 to 7.2 ppm as the duration of exposure on treated corn increased from 2 to 6 d. All second and third instar Indianmeal moth larvae died after a 5 d exposure period to corn grain treated with thiamethoxam at 50 ppm or higher, but as the larvae aged, higher concentrations and longer exposure periods were required to give 100% mortality of each larval instar. Similar results were obtained when larval Indianmeal moths were exposed on corn treated with imidacloprid, or on sorghum treated with thiamethoxam. Mature wandering phase fifth instars were the most tolerant larval stage of the Indianmeal moth.     

Susceptibility of Plodia interpunctella (Lepidoptera: Pyralidae) developmental stages to high temperatures used during structural heat treatments

Heating the ambient air of a whole, or a portion of a food-processing facility to 50 to 60 degrees C and maintaining these elevated temperatures for 24 to 36 h, is an old technology, referred to as heat treatment. There is renewed interest in adopting heat treatments around the world as a viable insect control alternative to fumigation with methyl bromide. There is limited published information on responses of the Indian meal moth, Plodia interpunctella (Hübner), exposed to elevated temperatures typically used during heat treatments. Time-mortality relationships were determined for eggs, fifth-instars (wandering-phase larvae), pupae, and adults of P. interpunctella exposed to five constant temperatures between 44 and 52 degrees C. Mortality of each stage increased with increasing temperature and exposure time. In general, fifth-instars were the most heat-tolerant stage at all temperatures tested. Exposure for a minimum of 34 min at 50 degrees C was required to kill 99% of the fifth-instars. It is proposed that heat treatments aimed at controlling fifth-instars should be able to control all other stages of P. interpunctella.     

Cold-Hardiness and Supercooling Capacity in Diapausing and Nondiapausing Stages of the Cabbage Root Fly Delia radicum

Supercooling point (SCP) values and cold-hardiness were measured in individual ontogenetic stages of Delia radicum (Diptera:Anthomyiidae) in various physiological states (winter diapause, summer quiescence, and normal development). Winter diapause-destined mature third-instar larvae had a lower SCP (-9.9 degrees C) than their nondiapause counterparts (-5.2 degrees C), and more of them survived exposure to -10 degrees C for 5 h to pupariation and adult emergence. Values of SCPs were equal in both diapause and nondiapause states of prepupal and pupal stages. The lowest SCP (ca. -20 degrees C) was found in the stage of phanerocephalic pupa (PCP) regardless of the physiological state. The cold-hardiness of PCP corresponded with a low SCP value only in diapausing pupae stored for 80 days at 3 degrees C and in pupae which had terminated their diapause and whose further development was inhibited by storage at low temperatures (3 degrees C). Such pupae survived exposure to temperatures close to their SCP (14 days at -17 degrees C). However, this high cold-hardiness was only acquired after some time and/or exposure to 3 degrees C, as the PCP at the beginning of diapause showed significantly impaired cold-hardiness despite the fact that their SCP was low. The cold-hardiness of nondiapausing PCP did not correspond at all to that of low SCP, as no pupa survived the exposure to -17 degrees C for 1 day; survival rates at temperatures of -13.5 and -10 degrees C were also remarkably lower than those in diapausing pupae. Cold-hardiness in D. radicum was closely connected with the diapause syndrome but the changes in SCP value corresponded rather with the ontogeny of this insect. Copyright 1993, 1999 Academic Press.     

Comparison of cold hardiness and sugar content between diapausing and nondiapausing pupae of the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

Abstract. To understand overwintering of the cotton boll worm Helicoverpa armigera, cold hardiness and sugar content are compared between diapausing and nondiapausing pupae. Diapausing and nondiapausing pupae reared at 20 °C under short and long photoperiods are acclimatized with a reduction of 5 °C per 5 days to 0 °C. When the acclimation temperature reaches 0 °C, the survival of diapausing pupae is assessed. The survival gradually decreases as the period of treatment progresses and approximately half survive for 112 days. However, nondiapausing pupae survive only 14 days after exposure to 0 °C. The surpercooling points of nondiapausing, diapausing and acclimatized pupae are approximately −17 °C. The major sugars contained in pupae are trehalose and glucose. Even though trehalose contents in diapausing pupae (initial level: 0.6 mg 100 mg⁻¹ fresh weight) increase significantly during cold acclimation and continue increasing until 58 days after exposure to 0 °C (maximum level: 1.8 mg 100 mg⁻¹), glucose is maintained at low levels (0.02 mg 100 mg⁻¹) for 56 days at 0 °C. However, glucose contents increase (maximum level: 0.8 mg 100 mg⁻¹) with decreasing contents of trehalose 84 days after exposure to 0 °C. Glycogen content gradually decreases during cold acclimation. When nondiapausing pupae are acclimatized with a reduction of 5 °C per 5 days to 5 °C from the beginning of pupation until the eyespots move, trehalose content increases (maximum level: 1.0 mg 100 mg⁻¹). Glucose contents in nondiapausing pupae increase before eclosion (0.09 mg 100 mg⁻¹). From these results, diapausing pupae of H. armigera can overwinter in regions where average winter temperatures are higher than 0 °C, but nondiapausing pupae cannot.     

Cold shock and cold tolerance in larvae and pupae of the blow fly, Lucilia sericata

Abstract.  Understanding the effects of low winter temperatures on mortality is essential in the development of a full understanding of the long-term population dynamics of any insect. The present study aims to examine the survival of pupae and larvae of the blow fly, Lucilia sericata , at overwintering temperatures. Groups of pupae and diapausing and nondiapausing third-stage larvae of L. sericata are maintained in cooled incubators at either 3 °C and 6 °C. Groups are removed from the incubators at 3–4-day intervals and transferred either to−8 °C or to 25 °C. After 1 h in the freezer, the larvae and pupae exposed to this cold-shock are also transferred to 25 °C. Larvae and pupae are then allowed to continue development and the number of adults emerging from each group is counted. The results demonstrate that survival decreases linearly with the period of exposure at both 3 °C and 6 °C. Mortality is higher at 3 °C than at 6 °C and, in groups that receive the cold shock, cold-shock reduces emergence by over 50%. However, there is no consistent tendency for diapausing larvae to survive prolonged cold or cold shock better than other life-cycle stages. The results suggest that the facultative development of an overwintering diapause stage in L. sericata does not appear to be an adaptation to enhance cold tolerance or resistance to cold shock. It is concluded that the survival of overwintering L. sericata is likely to be relatively less affected by low temperatures than it is by, for example, biotic factors, particularly given the buffered soil environment and short time-scales over which periods of cold act.     

Factors affecting carbohydrate and free amino acid content in overwintering larvae of Enosima leucotaeniella

Amounts of several metabolites were measured in overwintering larvae of Enosima leucotaeniella acclimated to temperatures between -5 and 15 degrees C for 30days. In the diapausing stage, cold hardiness, as shown by the survival rate, began rising below 15 degrees C. Glycogen content decreased as the temperature decreased from 10 to 0 degrees C. Trehalose content rose as the temperature decreased from 15 to 5 degrees C, but remained unchanged as the temperature decreased from 5 and 0 degrees C. Twenty-eight free amino acids were detected in the haemolymph; levels of proline, glutamine and glutamic acid increased at high temperatures, but alanine increased at low temperatures, especially as temperature decreased from 5 to 0 degrees C. Lipid content was unchanged by the different acclimation temperatures. The effects of temperature, diapause and aerobic conditions on the levels of carbohydrates and amino acids in overwintering larvae were analyzed. Alanine levels rose at low temperature only when the larvae were in the diapausing stage. The level of trehalose rose at low temperature in both the diapausing and post-diapausing stages, although it was higher at aerobic conditions in the post-diapausing stage. These results suggest that efficient trehalose synthesis occurs under the combination of low temperature and aerobic conditions of the post-diapausing stage, so that cold hardiness in overwintering E. leucotaeniella larvae may rise to a high level in winter.     

Observations on the intensity of diapause and cold tolerance in larvae from twelve populations and two reciprocal crosses of the Indian meal moth, Plodia interpunctella

ABSTRACT. The duration of diapause in larvae of Plodia interpunctella (Hübner) (Lepidoptera, Pyralidae) was assessed at 20°C in LD 11:13. Mean times from hatch to pupation for diapausing larvae from different populations ranged from 88 to 236 days. Most non-diapausing larvae pupated within 70 days at this temperature. Transferring diapausing larvae to 25°C and LD 9:15, or to 20°C and LD 15:9, 70 days after hatch reduced the subsequent mean time to pupation by 18–82% and 9–63% respectively. Only two population samples terminated diapause faster under LD 15:9 at 20°C than under LD 9:15 at 25°C. The mortality of diapausing larvae caused by 6- or 10-week exposures at 5, 7.5 or 10°C was generally less than 25%. Hybrids produced from a reciprocal cross between a temperate and a tropical African stock survived well. For other stocks there was some correlation between survival and diapause intensity. The low temperature regime which resulted in the greatest shortening of pupation time after return to the conditions used to induce diapause, did not always coincide with the temperature permitting the best survival. Results, however, indicate that some individuals of all stocks but one from the tropics are likely to survive in the U.K.