Physiological costs of cold exposure on the parasitoid <Emphasis Type="Italic">Aphidius ervi</Emphasis>, without selection pressure and under constant or fluctuating temperatures

The aim of this study is to evaluate the physiological costs and the consequences on fitness of cold exposure on the parasitoid Aphidius ervi (Hymenoptera: Aphidiinae) under non-lethal conditions. We exposed 1-day-old mummies to different treatments: control at 20°C, 7°C constant, 7°C fluctuating (7°C for 22 h and 20°C for 2 h). Two performances of fitness were particularly affected after two weeks at 7°C constant: female longevity and the sex ratio of the progeny was male biased. In contrast, egg load at emergence, lifetime fecundity, frequency of asymmetric individuals in both sexes, and mating success were not significantly affected under all treatments. The effects of these treatments on trends such as utilisation of fat reserves and fertility of males and females are discussed.     

What are the possible benefits of small size for energy‐constrained ectotherms in cold stress conditions?

In stressful environments, two main hypotheses have been proposed to explain the consequences of body size: (1) the absolute energy demand hypothesis (AED), which predicts that larger individuals are at a disadvantage under stressful conditions; (2) the relative efficiency hypothesis (RE), which predicts the reverse. We compared the effects of cold stress on different fitness traits of large and small individuals of the parasitoid wasp Aphidius ervi (Hymenoptera: Aphidiinae). For that, we exposed nymphs of this wasp to 5 treatment conditions as follows (control at 20°C; 7C1 and 7C2: constant cold temperature of 7°C for 1 and 2 weeks respectively; 4C1 and 4C2: constant cold temperature of 4°C for 1 and 2 weeks respectively). After cold stress, only the large females that emerged in the 7C2 and 4C2 treatments displayed a reduction in the fitness traits studied (longevity, egg load at emergence, life‐time fecundity). The decrease in lipid content in large adults may have been responsible for their lower fitness. Our results thereby supported the AED hypothesis. Furthermore, the small females in these treatments produced more eggs at emergence than the control females. This highlights the fact that in stressful environments, small females switch their reproductive strategy from a synovigenic strategy (in which females mature new eggs after emergence) to a more pro‐ovigenic one (in which females emerge with more mature eggs).     

Maternal and progeny quality of Habrobracon hebetor Say (Hymenoptera: Braconidae) after cold storage

The ectoparasitoid Habrobracon hebetor Say (Hymenoptera: Braconidae) is an important biological control agent for lepidopterous pests of stored products. We investigated the effects of low temperature storage on the quality of adult parasitoids and their progeny. Newly emerged females were stored for 10, 20, 30, 40, 50, and 70 days at 5 ± 1 °C. Several reproductive and developmental parameters were then assessed to determine the quality of the adult parasitoids and their progeny. After more than 30 days of storage, there was a decrease in parental parasitism, but low temperature storage of parents had no effect on parasitism of the F1 generation. Parental longevity and fecundity decreased after more than 20 days of storage, but there was no effect of storage duration on the fecundity and longevity of the F1 generation until a storage duration of 50 days. Development time varied with storage duration but differences were within 2 days. Storage duration had no effect on the sex ratio of F1 and F2 generations. Our data show that H. hebetor can be cold stored for up to 20 days without adversely affecting the performance of the parasitoid. Therefore, short-term storage of H.hebetor adults could be used for maintaining and accumulating large numbers of parasitoids in mass rearing programs.     

Effects of cold storage on Thripobius javae (=T. semiluteus) (Hymenoptera: Eulophidae)

Thripobius javae (Girault) was introduced in 1995 from Israel into Italy to control the greenhouse thrips, Heliothrips haemorrhoidalis (Bouché). Following introduction, successive augmentative releases of this parasitoid gave unsatisfactory and contradictory results, mainly due to the difficulty in synchronising its availability in sufficient number at the time of release. Efficient storage of this biological control agent could improve its current production and use. The effects of different sets of storage techniques at a single temperature and with a combination of different temperatures and instars on several fitness traits (residual developmental time to adult emergence after the end of storage, pupal mortality, longevity with and without hosts and progeny of emerged adults) were evaluated in order to determine the best conditions for storing the parasitoid.

For the pupal stage, increasing storage up to 14 days, at 10°C, gave only a moderate reduction (33%) of a modified composite quality index of its fitness. In contrast, when adults were stored for more than 10 days, at 15°C, residual longevity and progeny were reduced significantly. A combination of two temperatures (10 and 15°C) for pupal storage and a combination of pupal (10°C) and adult (15°C) storage had detrimental effects on parasitoid fitness. Temperatures of storage lower than 15 and 10°C had detrimental effects on adults and pupae, respectively.     

Cold storage of Trichogramma ostriniae reared on Sitotroga cerealella eggs

Efficient storage of the biological controlagent Trichogramma ostriniae couldimprove current parasitoid production methodsby making the system more flexible andefficient. Initial studies compared emergencerates of T. ostriniae reared onSitotroga cerealella eggs held at 6 °C, 9 °C, 12 °C,15 °C, and 24 °C for up to 8 weeks after parasitism.At 15 °C, emergence occurred in <2 weeks.Emeregence was >80% for parasitized eggsstored at 9 °C and 12 °C for 4 and 6 weeksrespectively. Storage at 6 °C caused asignificant decline in emergence after 2 weeks. Subsequent trials focused on fitness of storedT. ostriniae. Percentage of emergedfemales parasitizing eggs, female longevity,and fecundity were quantified after storage.The percentage of females successfullyparasitizing O. nubilalis eggs wasgreatest for the 9 °C four-week treatment(100%). Compared to 24 °C controls, storage at12 °C for 6 weeks or at 9 °C for 8 weeks reduced thepercentage of females parasitizing. Longevityof females held in cold storage was generallyless than that of controls. Rates of parasitismby stored Trichogramma was generallysimilar to controls after 2 to 4 weeks' storageat 9 °C and 12 °C but declined with storage longerthan 4 weeks. Emergence of progeny of cold-storedfemales was lower than controls for alltreatments. The percentage of female progenyfrom cold stored females was comparable tocontrols up to 4 weeks of storage.     

Side-effects of organic and synthetic pesticides on cold-stored diapausing prepupae of <Emphasis Type="Italic">Trichogramma cordubensis</Emphasis>

The side-effects of three insecticides (deltamethrin, lambda-cyhalothrin and Bacillus thuringiensis Berliner) and one fungicide (basic copper sulphate) were tested on cold-stored diapausing prepupae of Trichogramma cordubensis Vargas and Cabello (Hymenoptera: Trichogrammatidae). Pesticides were directly sprayed on parasitized host eggs (being the diapausing parasitoids in the prepupal stage) after cold storage (3°C) for three different periods (60, 120 and 180 days). Regardless of the period of cold storage, both pyrethroids reduced the emergence rates of T. cordubensis (both <25%) compared to the control (emergence varied from 83% to 89%). The most toxic pyrethroid was lambda-cyhalothrin; Trichogramma cordubensis adult emergence varied from 7% to 15%. Lambda-cyhalothrin also negatively affected the longevity and fecundity of parasitoids cold stored for 60 days. Bacillus thuringiensis Berliner subsp. kurstaki and basic copper sulphate had little or no adverse effect on emergence rates (generally >80%), longevity nor fecundity of T. cordubensis, indicating that these pesticides could be successfully integrated into pest management programs using wasps that were cold stored under diapause. Such integration would be valuable to pest management programs by reducing the costs of T. cordubensis mass rearing and by allowing producers to stockpile parasitoids for release in the growing season. However, since the emergence rate, longevity and fecundity of T. cordubensis generally decreased with increasing duration in cold storage, wasps to be used in integrated pest management programs should only be stored at 3°C for 60 days maximum. Handling Editor: Sam Cook.     

Temperature influences the performance and effectiveness of field and laboratory strains of the ichneumonid parasitoid, <Emphasis Type="Italic">Campoletis chlorideae</Emphasis>

To understand the influence of temperature on host–parasitoid interactions as a consequence of climatic change, we studied development, survival, and fecundity of field and laboratory strains of the Helicoverpa armigera larval endoparasitoid, Campoletis chlorideae at five different temperatures under laboratory conditions. Post-embryonic development period and degree-days required for completing the life cycle by both the strains decreased by 2.5 and 1.5 folds at 27°C compared to 18°C. Post embryonic development period showed a negative (r = −0.99, P < 0.001) and the development rate a positive (r = 0.99, P < 0.001) association with an increase in temperature. However, no parasitoid larvae survived in H. armigera larvae reared at 12 and 35°C after parasitization, suggesting that temperatures ≥35°C as a result of global warming will be lethal for development and survival of immature stages of C. chlorideae. Adult longevity was negatively associated (r = −0.91 to −0.96, P < 0.001) with temperatures between 12 and 35°C. The parasitoid adults stored at 12°C survived for longer period and exhibited higher fecundity than those kept at 27°C, but the efficiency of parasitism and adult emergence were quite low. Sex ratio of the progeny at 12°C was highly male-biased than the insects kept at 27°C. Laboratory strain of the parasitoid exhibited better survival, and the adults lived longer than the field strain at 18°C than at 27°C. Therefore, C. chlorideae adults stored at 18°C could be used for parasitism, while the immature stages should be reared at 27°C for mass production of the parasitoid for biological control of H. armigera.     

Cold tolerance of coccons ofAllorhogas pyralophagus [Hym.: Braconidae]

Cold tolerance studies were conducted under laboratory conditions for coccons ofAllorhogas pyralophagus Marsh, a Mexican parasitoid of graminaceous borers. By storage, developmental time (from cocoon to adult emergence) could be extended by 2 to 6 times. However, cocoons stored for more than 14 days at 2°C failed to survive, while at 5 and 10°C, about 50% emergence was recorded for upto 21 days of storage. With respect to survival and adult longevity, 10°C seemed to be the most suitable storage temperature. Pre-emergence period was also significantly increased by storing cocoons for 21 to 35 days at this temperature. Sex-ratio of emerging adults was not significantly affected by storage. Fecundity was adversely affected in all the treatments except in the case of females emerging from cocoons stored at 5°C for 7 days. The progeny of parasitoids which emerged from cocoons stored at 5 and 10°C for 35 days consisted of only males. It is clear from the present study thatA. pyralophagus cocoons are more amenable to short-term storage. Contribution No. 285/87 of the Indian Institute of Horticultural Research, Bangalore-560 089.     

Effect of different cold storage periods on parasitization performance of Trichogramma cacoeciae (Hymenoptera,Trichogrammatidae) on eggs of Ephestia kuehniella (Lepidoptera,Pyralidae)

The parasitism rates by Trichogramma cacoeciae Marchal (Hymenoptera, Trichogrammatidae) using Ephestia kuehniella Zell. (Lepidoptera, Pyralidae) eggs held at 0, 4 and 8°C and for up to 31 days was measured. Parasitism was lowest on eggs held at 8°C and highest on eggs held at 0°C. The highest parasitism, 97.8%, was measured for parasitoids attacking eggs held for 3 days and stored at 0°C. Parasitism of eggs stored at all three temperatures decreased with increasing duration of storage. The number of T. cacoeciae successfully developing and emerging as adults after storage in E. kuehniella eggs held at 0, 4 and 8°C was measured. Parasitoid emergence was >83% from E. kuehniella eggs stored at 8°C for 3 weeks. Storage at 0°C caused a significant decline in parasitoid emergence after 2 weeks (P<0.05). Storage at 0°C for more than 4 weeks reduced fecundity by 50%. T. cacoeciae parasitized the highest number of E. kuehniella eggs 1 day after adult emergence. The oviposition period lasted 6–7 days, although the parasitoids lived up to 13–14 days. Impact of storage time and temperature on parasitism rates by T. cacoeciae stored while in E. kuehniella eggs was measured. As storage time and temperature increased, subsequent parasitism rates of resulting adult T. cacoeciae decreased. Eggs of E. kuehniella can be stored at 0°C for up to 31 days. Trichogramma cacoeciae developing in eggs of E. kuehniella can be stored at 4°C for up to 5 weeks prior to release.     

Effects of fluctuating thermal regimes on cold survival and life history traits of the spotted wing Drosophila(Drosophila suzukii)

Drosophila suzukii is an invasive pest causing severe damages to a large panel of cultivated crops.To facili tate its biocontrol with stratcgies such as sterile or incompatible insect techniques,D.suzukid must be mass-produced and then stored and transported under low temperature.Prolonged cold exposure induces chill injuries that can be mitigated if the cold period is interrupted with short warming intervals,referred to as fluctuating thermal regimes(FTR).In this study,we tested how to optimally use FTR to extend the shelf life of D.suzukii under cold storage.Several FTR parameters were asessed:temperature(15,20,25℃),duration(0.5,1,2,3 h),and frequency(every 12,24,36,48 h)of warming intervals,in two wild-type lines and in two developmental stages(pupac and adults).Generally,FTR improved cold storage tolerance with respect to constant low temperatures(CLT).Cold mortality was lower when recovery temperature was 20℃ or higher,when duration was 2 h per day or longer,and when warming interruptions occurred frequently(every 12 or 24 h).Applying an optimized FTR protocol to adults greatly reduced cold mortality over long-term storage(up to 130 d).Consequences of FTR on fitness-related traits were also investigated.For adults,poststorage survival was unaffected by FTR,as was the case for female fecundity and male mating capacity.On the other hand,when cold storage occurred at pupal stage,postorage survival and male mating capacity were altered under CLT,but not under FTR.After storage of pupae,female fecundity was lower under FTR compared to CLT,suggesting an energy trade-off between repair of chill damages and C22 production.This study provides detailed information on the application and optimization of an FTR-based protocol for cold storage of D.suzuki that could be useful for the biocontrol of this pest.     

Biology of Australian and United States strains of Trissolcus basalis,a parasitoid of the green vegetable bug,Nezara viridula

Strains of Trissolcus basalis (Wollaston) Hymenoptera: Scelionidae, an egg parasitoid of the green vegetable bug, Nezara viridula (L.), were obtained from three regions of Australia and from Homestead, Florida (USA). Percent parasitoid emergence was approximately the same for freezer-stored (-75°C) and fresh eggs, and freezer-stored eggs were suitable hosts for a longer time. Optimum host age, oviposition and emergence patterns, mean number of progeny per female, sex ratio and longevity were examined and certain comparisons were made between the Australian and USA parasitoids. Genetic crosses made between males and females of each strain revealed that reproductive isolation did not occur. Higher fecundity of the Australian strains may make them more successful than indigenous (USA) strains for controlling pest populations of N. viridula in the southern USA.     

Effects of cold storage on life-history traits of Aphidius matricariae

Aphidius matricariae Haliday (Hymenoptera: Braconidae) is a polyphagous solitary endoparasitoid, attacking more than 40 species of aphids. This parasitoid is an important commercial product of many companies that produce biological control agents. Storage at low temperature increases the shelf life of many biocontrol agents, allowing companies to provide a steady and sufficient supply of insects for biocontrol programs. In the current study, the effects of cold storage of 1-day-old host mummies with A. matricariae for various time periods (5, 10, 15, 20, and 30 days) at 5 °C on the parasitoid’s key life-history traits were investigated. Parameters assessed after storage included adult emergence rate, offspring sex ratio, adult longevity, oviposition period, fecundity, and life-table parameters (R₀, r, λ, T, and DT). Our results showed that the mummies of A. matricariae could be stored at 5 °C for 5 days without loss of quality and for 10–15 days with minimal reduction in quality (e.g., some reduction in adult longevity and R₀). If parasitoids were stored for >15 days, quality was more strongly affected. In conclusion, A. matricariae pupae could be stored at 5 °C for up to 15 days without significant negative post-storage effects on fitness of the parasitoid. These results could be used to improve the planning of mass rearing and mass release of A. matricariae in augmentative biological control programs.     

Effect of temperature on the reproductive biology of Peristenus spretus (Hymenoptera: Braconidae), a biological control agent of the plant bug Apolygus lucorum (Hemiptera: Miridae)

Peristenus spretus Chen et van Achterberg (Hymenoptera: Braconidae), a parasitoid of the plant bug Apolygus lucorum (Hemiptera: Miridae), has been studied for use in augmentative biological control in China. Under laboratory conditions, we explored the development, survival, age-specific and potential lifetime fecundity, oviposition period and progeny sex ratio of P. spretus reared at six constant temperatures (15°C, 19°C, 23°C, 27°C, 31°C, 35°C) on the second instar nymphs of A. lucorum. At 15°C, male and female P. spretus took 48.7 ± 0.3 and 52.5 ± 0.3 days to complete their immature development, while developmental time was reduced by more than half at 23°C and 27°C. The parasitoid can only develop to the larval stage at 31°C and neither larva nor pupa survived at 35°C. The estimated lower developmental threshold of the immature stage was 7.3°C. When parasitoid adults were exposed at 15°C, females laid 90% of their eggs at first 19 days of oviposition and had an extended reproductive life. In contrast, females held at 27°C laid most of their eggs (90%) in their first of 10 days of oviposition and had shorter longevity. The highest potential lifetime fecundity of P. spretus was 671.2 ± 34.7 SE eggs produced over 23.4 ± 1.4 SE days at 23°C. At 15°C, 19°C and 23°C, sex ratios of reared parasitoids were male-biased, but at 27°C there was no male bias.     

Effect of temperature on the development, fecundity, progeny sex ratio and life-table of Campoletis chlorideae, an endolarval parasitoid of the pod borer, Helicoverpa armigera

Development, survival, fecundity, progeny sex ratio (PSR) and age-specific life-table parameters of the parasitoid Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) were examined at six different constant temperatures (12, 17, 22, 27, 32 and 37°C) in the laboratory [70 ± 10% RH and 10:14 h (light:dark) photoperiod]. Second instar larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were reared on chickpea (Cicer arietinum L.) and used as the host. Development times shortened as the temperature increased from 12 to 37°C. The estimated lower developmental threshold (tL) was 3.4°C. The thermal summation for total immature stages was 379.97 degree-days. A reciprocal relationship between temperature and longevity was observed in the range of 12–17°C. The maximum mortality of pupae (71.8%) occurred at 37°C. At 22°C, the yield of a female parasitoid averaged 137.3 ± 14.7 (mean ± SD) progeny, of which 89.6 ± 7.6 were daughters. The number of daughters produced decreased when the females were kept either above or below 22°C, although the PSR was female biased in the range of 17–27°C. The analyses of life-table parameters, developmental rates, reproduction, mortality and PSR suggest that maximum population growth (r _m ) is near 27°C. There was little variation observed in most of the desired qualities of C. chlorideae in the range of 17–27°C, and it appears that the parasitoid is adapted to a wide range of temperatures. We suggest that for maximum production the parasitoid should be reared at 22 ± 4°C and be released in areas where the temperature ranges between 17° and 27°C, as in the plains of northern India.     

Refrigeration of Riptortus clavatus (Hemiptera: Alydidae) eggs for the parasitization by Gryon japonicum (Hymenoptera: Scelionidae)

Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) is a solitary egg parasitoid of Riptortus clavatus (Thunberg) (Hemiptera: Alydidae) one of the most important pests in soybean in Korean and Japan. Refrigeration of R. clavatus eggs for up to 120 days was evaluated as a method of mass production of G. japonicum. The refrigeration reduced the eclosion of eggs, thus no nymph emerged after 30 days of egg refrigeration. Increased duration of host acceptance behaviors by G. japonicum and some detrimental effects on parasitism rate, developmental time, longevity, and adult size of the parasitoid were found in refrigerated host eggs. However, all the biological parameters of G. japonicum were unaffected by the refrigeration of up to 30 days. Gryon japonicum parasitized 16 and 14 host eggs daily that were refrigerated for 15 and 30 days, respectively, which did not differ from parasitization of fresh host eggs. Furthermore, refrigeration of host eggs did not reduce the reproduction of the emerged adult parasitoids and emergence and sex ratio of their progeny. Gryon japonicum also parasitized 14 and 13 refrigerated host eggs per day kept at 26.3°C and 78.7% RH for 2 and 4 days of post-refrigeration without significant reduction, respectively. These results show that refrigeration of R. clavatus eggs can be a good method for mass rearing of the parasitoid, and the host eggs killed by cold storage can be supplemented in the field to boost field parasitism.     

Effect of hypoxia and its repercussions in packing pupae of the parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) for shipment

Hypoxia periods of 6, 12, 24, 48, and 72?h combined with temperatures of 15°C, 20°C and 25°C were applied to Diachasmimorpha longicaudata pupae in packaging conditions. Alternating temperatures of 26–20–26°C were applied to pupae in three sequential 4-h periods less than 12?h of hypoxia, and the effect of hypoxia on the pupae was evaluated under ambient conditions in commercial shipping. The emergence, longevity, fecundity and flight ability of adult parasitoids were recorded. The duration of hypoxia (>24?h) and the higher temperature (25°C) significantly reduced the emergence and longevity of adults. The different temperatures, including the variation in temperature combined with hypoxia, showed no significant effect on fecundity or flight ability. The temperature and humidity recorded during commercial shipping under hypoxia did not show any effect on the emergence of parasitoids. As a consequence, hypoxia was only notably significant after 24?h, which occasionally occurs in practical packaging processes. The use of hypoxia for shipping D. longicaudata pupae can be widely recommended, but long shipping periods and high temperatures should still be avoided.     

Quality assessment of Riptortus pedestris (Hemiptera: Alydidae) eggs cold-stored at different temperature and relative humidity regime

Supplementation of host resource can be more economical method for the biological control of insect pest compared to direct release of adult parasitoids. Periodical release of non-viable cold-stored eggs of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) has been found to enhance parasitism of this pest in soybean fields. To find the optimum environmental conditions for cold storage of these host eggs, we evaluated nine different combinations of temperature (2, 6, and 10 °C) and relative humidity (high 90–95%, medium 70–75%, and low 30–35%). After 30 d of cold-storage, eggs were weighed and held at 26.6 °C and 75% relative humidity for 8 d before testing. To test the eggs’ suitability as hosts following cold storage, females of Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) were released individually onto batches of eggs, and parasitization rates and the development, emergence, sex ratio, adult longevity, and size of parasitoid progeny were examined. Eggs stored at high relative humidity showed less weight loss than those stored at low relative humidity. The number of eggs parasitized was highest (5.9/15) on eggs stored at 6 °C and high relative humidity. Developmental times and adult emergence were optimal on host eggs stored at 2 °C and high relative humidity. A significantly lower proportion of eggs produced male parasitoids when eggs were stored at 2 or 6 °C. Adult longevity was not affected by egg storage conditions, but adult size of progeny decreased in eggs stored at 10 °C. In conclusion, eggs of R. pedestris stored below 6 °C and with a high relative humidity maintained the best quality for parasitization by O. nezarae.     

Incidence of superparasitism in the egg parasitoid,Ooencyrtus kuvanae Howard (Hymenoptera: Encyrtidae)

The encyrtid Ooencyrtus kuvanae is a solitary parasitoid of the gypsy moth, Lymantria dispar L. (Lepidoptera-Lymantridae) that is used in biological control programmes and whose mass rearing is influenced by superparasitism. The purpose of this study was to investigate the effect of the self-superparasitism of O. kuvanae at different host densities (5, 10, 15 and 20), female ages (3 and 5 days) and durations of exposure (1 and 5 days) under various laboratory conditions (25°C?±?1°C, RH 60?±?5% and a 16:8?h light:dark photoperiod) as well as in a new laboratory host, Philosamia ricini (Danovan) (Lepidoptera: Saturniidae) of O. kuvanae. In this study, we determined the rate of egg superparasitism and adult emergence and recorded development time, longevity and body weight. Superparasitism increased with female age and the duration of exposure to parasitoids when females had access to five host eggs. Superparasitism increased the number of parasitoid offspring, but it resulted in male-biased (56.90%) progeny. Furthermore, superparasitism caused deleterious effects to the fitness of the progeny by prolonging the developmental process, and decreasing longevity. For example, we found that when four adults can emerge from one superparasitised host egg, the body size of the parasitoid offspring decreases significantly. Hence, superparasitism should be avoided when mass rearing O. kuvanae.     

Influence of larval rearing temperature on the quality of cold‐stored Oomyzus sokolowskii Kurdjumov (Hymenoptera: Eulophidae)

Oomyzus sokolowskii, an important parasitoid of Plutella xylostella, has great potential for use in biological control. Storage at suboptimal temperature is valuable for increasing the shelf‐life of insect parasitoids. In this study, O. sokolowskii larvae were reared at 30/25, 25/25 and 25/20°C light/dark (65 ± 5% RH, 16 : 8 h L : D) until pupation. The pupae were then cold‐stored at 4 ± 1°C (60 ± 5% RH, full darkness). The pupae were removed out from the storage at 10, 20, 30 and 40 days after storage (DAS) and maintained at 25 ± 2°C until adults emerged or pupae died. Quality of the emerging adults and their F₁ offspring were assessed. Incidence of parasitism by O. sokolowskii was higher at 30/25°C than at 25/20°C. Cold storage of O. sokolowskii pupae greatly affected the fitness of the parasitoid: adult emergence rates were lower in the 40 DAS treatment than in other treatments; when O. sokolowskii larvae developed at 25/25°C, female proportions of the emerged adults were lower in the 40 DAS treatment than in the 0 and 10 DAS treatments. Larval rearing temperature mildly affected the adult emergence rate, post‐storage developmental time and female proportion with a few exceptions. Number of parasitoids emerged per host pupa, and incidence of parasitism by the females were neither affected by larval rearing temperature nor cold storage duration. Trans‐generational effects on F₁ offspring were evident in adult emergence rate, egg‐adult developmental time and female proportion which were negatively affected by long duration of storage (40 days), but not by larval rearing temperature with a few exceptions. In conclusion, O. sokolowskii pupae could be stored at 4°C for up to 30 days without significant fitness loss.     

Effects of temperature on the development and fecundity of Microplitis similis (Hymenoptera: Braconidae), a parasitoid of Spodoptera litura (Lepidoptera: Noctuidae)

Microplitis similis (Hymenoptera: Braconidae) is a solitary endoparasitoid of Spodoptera litura larvae (Lepidoptera: Noctuidae). Here, the effects of constant temperature (18, 21, 24, 27, 30, 33 and 36 °C) on the development and fecundity of M. similis developing in S. litura were studied in the laboratory to clarify the range of its potential distribution and better understand its potential as a biological control agent. The developmental duration of M. similis varied from 10.6 (33 °C) to 27.9 days (18 °C). The developmental threshold temperature and effective accumulative temperature of M. similis were 9.96 °C and 231.14 Degree-days, respectively. The average adult longevity of M. similis ranged from 5.1 (33 °C) to 26.8 days (18 °C). The maximum fecundity of the parasitoid was observed at 27 and 30 °C, which were 43.07 and 39.73 eggs, respectively. The minimum fecundity of the parasitoid was observed at 18 °C, which was 8.27 eggs. The intrinsic rate of increase (r_m) and finite rate of increase (λ) of M. similis were the highest at 30 °C. The net reproduction rate (R₀) was the highest at 27 °C and 30 °C, which were 44.34 and 40.39, respectively. We concluded that temperatures in the range 27–30 °C are the most suitable for development and reproduction of M. similis. Our study provides detailed basic information for development and reproduction of M. similis under different temperature conditions.