Impact of Vairimorpha sp (Microsporidia : Burnellidae) on Trichogramma chilonis (Hymenoptera, Trichogrammalidae), a hymenopteran parasitoid of the cabbage moth, Plutella xylostella (Lepidoptera, Yponomeutidae)

A multi-generation mass breeding colony of the cabbage moth, Plutella xylos tella, was found to be infected with a microsporidium, Vairimorpha sp., whi ch is passed transovarially between generations. The microsporidian infecti on had little impact on the fitness of this lepidopteran pest. However when Trichogramma chilonis parasitized such infected host eggs, the offspring o f this parasitoid species suffered from severe deficiencies. Microsporidian spores, ingested by parasitoid larvae together with the host egg nutrients , gave rise to stages which developed in various tissues of the parasitoid, such as the flight muscle and the nervous system. This infection resulted in a significantly increased rate of metamorphosis failure (related to host age) and reduced longevity and reproductive performance of the parasitoids . There are two main consequences arising from our findings if T. chilonis is to be used in an integrated control strategy against P. xylostella: (1) T. chilonis must be raised on Vairimorpha-free host eggs to receive viable and efficaceous parasitoids for release and (2) if natural populations of t he cabbage moth in cruciferous crops are infected with Vairimorpha to a sig nificant extent, the parasitoid must be released repeatedly within infested crop areas. (C) 1999 Academic Press.