RAPID DETERIORATION OF SEARCHING BEHAVIOR, HOST DESTRUCTION, AND FECUNDITY OF THE PARASITOID MUSCIDIFURAX-RAPTOR (HYMENOPTERA, PTEROMALIDAE) IN CULTURE

Muscidifurax raptor Girault & Sanders that had been in culture for seven generations (collected in 1987, strain MR87) were larger, killed more house fly pupae, produced more progeny, and had superior host-searching ability than parasitoids that had been in culture for 94 generations (collected in 1982, strain MR82). After 17 generations, attack rates of MR87 declined to equal those of MR82 and were substantially lower than those of MR82 after 42 generations. Heritability, based on mother-daughter regressions, was 0.52 for wing length and impossibly high (h2, 1.56) for fecundity, indicating that fecundity is largely determined by nonchromosomal maternal influences. Single-pair reciprocal crosses between strains confirmed that fecundity was influenced by a maternal effect, although hybrids showed evidence of positive heterosis as well. Attack rates and progeny production by parasitoids collected from the field in 1990 declined by 50% after only two generations in culture. The results are best explained by a combination of a maternally transmitted pathogen that is amplified in the laboratory and, to a lesser extent, inbreeding depression. Examination of cultures after the conclusion of the experiments revealed infections of most colonies with an undetermined microsporidium.