Egg Parasitoids (Hymenoptera; Trichogrammatidae) of Diopsis Macrophthalma (Diptera; Diopsidae) in Malawi

Abstract

In Malawi, during the study period eggs of the rice-borer Diopsis macrophthalma were mainly parasitized by Trichogramma kalkae and Trichogramma pinneyi and further by Trichogrammatoidea simmondsi and a Paracentrobia species. Data are presented on rates of parasitism, locations and sizes of parasitized eggs, fecundity, longevity, development time, number of exit holes, clutch size per host egg, sex-ratio, emergence rate,alternative hosts and super- and multiple parasitism. Relations are discussed between 1) development time and clutch size, 2) number of ♂♂ per host egg and exit holes, 3) oviposition rate and host egg size and 4) sex-ratio and clutch size. In the first three parasitoids mentioned a fertilization/oviposition system is found that favours the presence of one♂ and a certain number of ♀♀ per Diopsis egg. Evidence is put forward that a fixed sex-regulation system exists during oviposition. T. kalkae was the most important egg parasitoid of D. macrophthalma, followed by T. pinneyi. No other hosts were found for T. kalkae, whereas T. pinneyi had one alternative main host and some hosts of lesser importance. In competition for eggs of D. macrophthalma T. kalkae was in various ways superior to T. pinneyi. This latter species seems more adapted to smaller host eggs.