Background and Objectives
Bracon hebetor Say is a well-known cosmopolitan ectoparasitoid that attacks the larvae of various lepidopteran pests, especially cotton boll worm, Helicoverpa armigera. Cold storage is a general technique for long-term preservation of this parasitoid in insectaries. Most parasitoids require sugar supplemental sources as a source of energy in adult stage. Because of the need to enhance cold storage efficacy in commercial insectaries, this study was carried out to assess effects of feeding frequencies and mating status on biological and reproductive characteristics of maternal wasps and their progeny (F1) stored in refrigerator (5±1˚C) for two durations of 7 and 14 days.
Materials and Methods
B. hebetor reared on the 4-5 instars larvae of Anagasta kuehniella in a climate-controlled room, at 26 ± 2˚C, 50±5% RH, and a 16:8 (L:D)h. photoperiod. The effect of feeding frequency was studied in three levels of "without feeding" (starved wasps), "one-time feeding" before cold storage, and "two-time feedings" (before and during cold storage). Mating status was investigated in two "mated" and "unmated" levels. After each treatment, adult parasitoids were stored inside a refrigerator (5±1˚C) for two periods of 7 and 14 days, and mortality, longevity and fecundity of maternal parasitoids were subsequently assessed. Immature’s developmental time and mortality, percentage of adult emergence and sex ratio were also investigated for progenies in next generation. The experiment was carried out using a factorial experimental design and obtained data were analyzed using SAS software, and LSD mean comparison test.
Results showed that sugar feeding and mating of parasitoid before beginning of cold storage decreased mortality during storage and increased fecundity compared to starved and unmated wasps. The highest mortality of females (33.2%) was observed in starved and unmated wasps that were stored in refrigerator for 14 days. In contrast, the lowest mortality of females (7.71%) belonged to mated parasitoids that fed twice (before and during cold storage) on honey solution and stored for 7 days. Feeding on honey solution by maternal adult parasitoids reduced immature’s mortality and their developmental time in progenies of next generation. Means of immature’s mortality and developmental time in fed wasps (22.82 percent and 11.17 days, respectively) were significantly lower than starved ones (30.64 percent and 11.77 days, respectively).
According to our results, feeding on honey solution increased cold-tolerance of both male and female B. hebetor adults. So that, honey-fed adult parasitoids had lower mortality and higher fecundity than starved ones. Similar to feeding, our results showed that mated parasitoids had higher survival and fecundity than unmated ones. Also, feeding and mating of cold-stored maternal parasitoids had a positive effect on the survival and development of progenies in next generation. In conclusion, spraying honey solution on the rearing cages of B. hebetor and providing sufficient time for mating before storing in refrigerator, are recommended to improved cold-storage efficacy of this parasitoid in insectaries.