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New Zealand Plant Protection 65 (2012): 294

Effects of host and foundress density on reproductive strategy of Diaeretiella rapae

R. Kant, M.A. Minor, S.A. Trewick and W.R.M. Sandanayaka

ABSTRACT

The reproductive fitness of a parasitoid depends on the oviposition decisions of a female in response to competition. The present study investigated the oviposition and sex ratio of offspring produced by the parasitic wasp Diaeretiella rapae while competing with other conspecific females and at different host densities. The number of Brevicoryne brassicae nymphs parasitised by female D. rapae increased with the number of nymphs offered to them. However, the proportion of nymphs parasitised by the female decreased when nymph density was high. The proportion of fertilised eggs oviposited by females decreased when nymph density increased. An increase in the number of foundresses (females ovpositing together) increased the total parasitism, but the contribution of each female (the number of nymphs each female parasitised) decreased. Smaller proportions of female offspring were produced when females were competing for the same hosts. The results of this study suggest that both host and foundress densities asymmetrically affect progeny production and sex allocation in this species.

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