Wolbachia density and host fitness components in Muscidifurax uniraptor (Hymenoptera : Pteromalidae)

Intracellular bacteria of the genus Wolbachia are found in a variety of art hropod hosts, where they cause various reproductive disorders. Attempts to study the fitness advantages and disadvantages of carrying these symbionts have yielded contradicting results. Using various doses of the antibiotic r ifampicin, we were able to manipulate the density of Wolbachia in the unipa rental parasitoid Muscidifurax uniraptor (Hymenoptera: Pteromalidae). The e ffect of different titers of the symbiont on the fecundity, reproductive ra te, longevity, survival rate, and sex ratio of the host was measured. The d ata gathered show that following antibiotic treatments, the percentage of m ales rises at low doses of rifampicin and then drops again. The total sex r atio of offspring produced by treated mothers was positively correlated wit h the numbers of Wol- bachia found in eggs laid by these females. No signif icant effects were detected with regard to the other studied fitness compon ents. It is concluded that in M. uniraptor, Wolbachia are not posing any bu rden on the life history trait studied. (C) 2000 Academic Press.