Abstract
Functional response is usually used to evaluate the potential of a parasitoid or predator in regulating the population of a pest and hence, is an important tool in the selection of appropriate biological control agents for a particular pest. This study aimed to investigate the functional response of the parasitoid, Dirhinus giffardii Silvestri (Hymenoptera: Chalcididae) towards two Bactrocera species (Diptera: Tephritidae), B. zonata (Saunders) and B. cucurbitae (Coquillett); each offered at seven different densities (10, 20, 30, 40, 50, 70 or 100 pupae) for a period of 24 h in cylindrical plastic cages in the laboratory. The results showed a type II functional response of D. giffardii towards both the fruit fly species, B. zonata and B. cucurbitae. The parasitoid exhibited a higher attack rate (a) (0.8235 vs. 0.6798), a shorter handling time (T-h) (0.5160 vs. 0.7344) and a higher maximum parasitism rate (T/T-h) (46.52 vs. 32.69) on the pupae of B. zonata than on the pupae of B. cucurbitae. Consequently, the parasitoid was more effective on B. zonata than on B. cucurbitae. Offspring sex ratio of the parasitoids was female biased regardless of the host fruit fly species. The results suggest that D. giffardii could be a more efficient biological control agent for B. zonata than for B. cucurbitae.