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Dispersal in Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae) and its importance to biological control programs Gadsby, Margaret Carol


The dispersal of Phytoseiulus persimilis Athias-Henriot, a predatory phytoseiid mite used in biological control of the phytophagous two-spotted spider mite, Tetranychus urticae Koch, has been largely ignored to the detriment of control programs. In this thesis, three aspects of behaviour were studied over the developmental period of the predator and related to dispersal. Two predictive indices for dispersal were derived. Dispersive tendency was induced in adult female predators by confining them at high density (10 per capillary tube) and starving them for 24 hours. Dispersers were characterized behaviourally. Dispersers were typically geopositive and displayed an ability and strong tendency to distinguish edges and follow them. Dispersers moved at speeds three times greater than normal individuals, and were less efficient predators. Dispersers moved onto a novel substrate five times faster than normal individuals. Induced dispersal behaviour persisted for 40-46 hours after release, even when predators were provided with ample prey. When released onto infested bean and cucumber plants, dispersive mites exercised poorer control on the pest population than non-dispersive predators. Prey numbers were greater and plant damage was more severe and less localized. On the young leaves of cucumber plants, predator egg placement was not harmonious with prey distribution. The potentially disruptive affect of dispersal on control programs is discussed. A re-evaluation of predatory efficiency in the light of this result is recommended. The need to assess the dispersive tendency of stock populations of the predator and eliminate those which are "too" prone to disperse is stressed. The impact of standard pre-release methods which apparently induce dispersal on greenhouse control programs is also discussed. The need to assess stocks which form the basis for organophosphate-resistance selection programs is also addressed. Cannibalism, inter-male aggression, substrate preference, and oviposition site selection in P. persimilis are also discussed.

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