Adult size and timing of reproduction in five species of Asobara parasitoid wasps.

The majority of adult parasitoid wasps are unable to synthesize lipids and therefore face a trade-off between the investment of lipids in eggs or in the maintenance of soma. It has been shown that resource allocation should depend on body size in parasitoids. Given that smaller females have shorter expected life times, they should concentrate their reproductive effort into early life. To test this prediction, we investigated the relationship between body size and the timing of egg production in parasitoids. We measured body size, lipid reserves, and reproductive investment (number of eggs, ovigeny index equivalent [OIE] and egg size) at eclosion in five species of Asobara (Hymenoptera: Braconidae) originating from different geographic and climatic environments. Our results show significant interspecific variation in all these traits. A diagnostic test for phylogenetic independence revealed that closely related species did not resemble each other more closely than expected by chance for all traits measured. Lipid reserves scaled positively with body size both between and within species. In agreement with theory, OI correlated negatively with body size both between and within species. Total egg area at eclosion correlated negatively with lipid reserves both between and within species. This indicates the existence of a trade-off between allocation of lipids to current reproduction and survival/future reproduction. With the exception of the most extreme pro-ovigenic species, A. persimilis, we found that pro-ovigeny was compensated for by small egg size. Our results indicate the role of habitats in shaping interspecific variation in resource allocation strategies.

Effect of Arsenophonus Endosymbiont Elimination on Fitness of the Date Palm Hopper, Ommatissus lybicus (Hemiptera: Tropiduchidae).

The date palm hopper, Ommatissus lybicus de Bergevin, is one of the most important pests of the date palm in the Middle East and North Africa. This insect uses its needle-like sucking mouthparts to feed on phloem, which is devoid of most essential amino acids and many vitamins. The absence of essential nutrient in its diet is suggested to be ameliorated by endosymbionts in O. lybicus. Arsenophonus is one of the main bacterial endosymbionts widely prevalent in O. lybicus. In this study, we used antibiotics to eliminate Arsenophonus from O. lybicus originating from three populations (Fin, Qale'e Qazi, and Roodan) and studied the effects on the fitness of the pest. Our results revealed that the removal of Arsenophonus increased the developmental time of the immature stages and reduced the values of different life-history parameters including nymphal survival rate and adult longevity in the host. Furthermore, elimination of Arsenophonus completely obliterated offspring production in all O. lybicus populations investigated. These results confirm the dependency of O. lybicus on Arsenophonus for fitness and give a new insight regarding the possibility of symbiotic control of O. lybicus.

Mating and Carbohydrate Feeding Impacts on Life-History Traits of Habrobracon hebetor (Hymenoptera: Braconidae).

Rapid population growth and wide host range make Habrobracon hebetor Say (Hymenoptera: Braconidae) highly suitable for biological control programs. To improve performance of the reared wasps in biological control programs we conducted a series of experiments on the effect of mating and carbohydrate feeding on life-history traits of this parasitoid. Mating caused a significant cost to fecundity, host paralysis and parasitism ability of H. hebetor. Mated wasps produced 30.98 and 23.2% less progeny than virgin wasps in unfed and fed treatments, respectively. Carbohydrate feeding increased survival only in the absence of host larvae. Virgin wasps produced only male offspring while the sex ratio produced by mated females was close to 50/50 for both fed and unfed wasps. Virgin wasps demonstrated an aggressive parasitism behavior and significantly higher paralysis and parasitism rates compared to mated wasps. Virgin wasps fed with carbohydrate found significantly more hosts than unfed wasps. To conclude, mating disruption in H. hebetor resulted in an aggressive parasitism behavior in the laboratory, which may also occur in the field. Therefore mating disruption is expected to improve the efficacy of these parasitoids in biocontrol. Carbohydrate feeding only improved searching ability and host allocation and could be applied in situations where hosts are highly dispersed.

Temperature and Exposure Time in Cold Storage Reshape Parasitic Performance of Habrobracon hebetor (Hymenoptera: Braconidae).

Cold storage can extend shelf life of parasitoids for use in biocontrol. However, cold storage may have negative impacts on life history traits of the parasitoids and, therefore, on their performance as biocontrol agents. Here, we examine the effect of cold storage on life history traits of Habrobracon hebetor (Say) (Hymenoptera: Braconidae), a parasitoid of several economic lepidopteran pests. Newly emerged wasps were stored at three constant temperatures (3°C, 5°C, 7°C) for up to 4 wk. Both temperature and exposure time significantly affected longevity, parasitism, fecundity, and sex ratio. Significant reduction in longevity was observed at 3°C and 7°C, whereas longevity of wasps stored at 5°C remained stable up to the second week and then gradually decreased in Weeks 3 and 4. Parasitism rate also significantly decreased after cold storage at 3°C, 5°C, and 7°C (ranked from high to low). Fecundity decreased at T 3°C and T 5°C but this trait was not affected by storage at T 7°C. A significant shift in male production was observed at T 5°C in Week 3, but in Week 4, the only treatment with male biased reproduction was T 3°C. These results show that the effect of temperature and exposure time in cold storage is trait dependent. Overall, storage at 5°C for a period of 3 wk least impacted most life-history traits of H. hebetor wasps.