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 Steffan was st udied when reared on eggs of the bruchid storage pest, Callosobruchus maculatus (Fabricius) developing in seeds of cowpea, chickpea and pige onpea. The beetle laid more and larger eggs on pigeonpea than on cowpe a and chickpea, indicating that there was not a trade-off between numb er and size of the eggs. The bruchid larvae reared on pigeonpea exhibi ted a longer development time and a higher mortality than those reared on cowpea and chickpea. The resulting males weighed less than those r eared on cowpea and chickpea. The trichogrammatid U. lariophaga parasi tized more eggs when C. maculatus was reared on chickpea than when rea red on the other hosts. Parasitoid larvae developed slowest and had th e highest mortality in eggs of C. maculatus reared on pigeonpea compar ed to those reared on cowpea and chickpea; the sex ratio (% of females ) of the resulting adults was also higher. The high mortality and long development time of C. maculatus reared on pigeonpea indicated that t his legume was less favourable to C. maculatus than chickpea or cowpea . This was probably also true for the parasitoid since the mortality w as higher and development longer in eggs of C. maculatus reared on pig eonpea compared to those reared on cowpea and chickpea. Therefore, whe n host eggs were larger and of lower nutritional quality, the proporti on of female egg parasitoids was greater.