The effect of leguminous plant species on Callosobruchus maculatus (Coleoptera: Bruchidae) and its egg parasitoid Uscana lariophaga (Hymenoptera: Trichogrammatidae).
The performance of the egg parasitoid Uscana lariophaga was studied when reared on eggs of the bruchid Callosobruchus maculatus developing in seeds of cowpeas, chickpeas and pigeon peas. The bruchid laid more and larger eggs on pigeon peas than on cowpeas and chickpeas, indicating that there was no trade-off between number and size of the eggs. Bruchid larvae reared on pigeon peas exhibited a longer development time and a higher mortality than those reared on cowpeas and chickpeas. The resulting males weighed less than those reared on cowpeas and chickpeas. U. lariophaga parasitized more eggs when C. maculatus was reared on chickpeas than when reared on the other hosts. Parasitoid larvae developed slowest and had the highest mortality in eggs of C. maculatus reared on pigeonpeas compared to those reared on cowpeas and chickpeas; the sex ratio (percentage of females) of the resulting adults was also higher. The high mortality and long development time of C. maculatus reared on pigeon peas indicated that this legume was less favourable to C. maculatus than chickpeas or cowpeas. This was probably also true for the parasitoid since mortality was higher and development longer in eggs of C. maculatus reared on pigeon peas compared to those reared on cowpeas and chickpeas. Therefore, when host eggs were larger and of lower nutritional quality, the proportion of female egg parasitoids was greater.