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The host-selection behaviour of nine strains of Trichogramma spp., towards eggs of Mamestra brassicae, Pieris brassicae and P. rapae, was investigated in laboratory experiments in order to select candidate strains for inundative releases against these species. Experiments were carried out by continuously observing the behaviour of individual females, which were offered equal numbers of eggs of two host species arranged in a grid. M. brassicae was a highly acceptable host species for all strains, whereas the acceptability of the two Pieris species was similar within strains, but varied between strains. Considering the variation in acceptance of Pieris eggs, strains either showed: (1) no preference between Mamestra and Pieris (High Pieris Acceptance = HPA strains), (2)a preference for Mamestra (Variable Pieris Acceptance = VIA strains), or (3) an aversion for Pieris (Low Pieris Acceptance = LPA strains). Females of VPA strains showed a high acceptance of Pieris eggs if the preferred Mamestra eggs were absent. They contacted comparatively fewer Pieris eggs in presence of Mamestra eggs, which indicates selection of hosts at a distance. HPA strains probably are the best candidates for inundative releases.

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