The Reproductive Strategy of a Parasitic Wasp: II. Sex Allocation and Local Mate Competition in Trichogramma evanescens

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Abstract
The theory of local mate competition (LMC) predicts that optimal sex ratio in parasitic wasps will change as the number of female parasitoids exploiting a particular patch of host resource varies. The predictions of LMC models of Hamilton (1979) and Werren (1980) are examined using the parasitoid, T. evanescens Westwood, attacking patches of its host, the eggs of the moth, Mamestra brassicae L. Experimental results are in broad agreement with model predictions. A behavioral analysis reveals little evidence that wasps respond to the presence of other wasps on the patch. Adaptive sex ratio changes are generated largely by the sequence in which male and female progeny are deposited in host patches. By this simple pattern of sex allocation, Trichogramma is able to make adaptive responses to changes in both size of resource patches and the number of wasps competing for them. The implications for mass production of Trichogramma for biological control are discussed.