The effect of powdery mildew on the number of prey consumed byTyphlodromus pyri(Acari: Phytoseiidae).

Prey consumption byTyphlodromus pyriScheuten was studied in the presence and absence of apple powdery mildew,Podosphaera leucotricha(Ell. and Everh.) under constant laboratory conditions. Eggs ofTetranychus urticaeKoch were offered to predatory mites as a prey. Seven densities ranging from five to 100T. urticaeeggs per arena were used. Mildew conidia (approximately 0.5 mg) were added to half of the arenas by brushing them from infected apple leaves. A single adult female ofT. pyriwas introduced onto each arena and number of prey eggs consumed was counted 12 h later when the predator was offered newT. urticaeeggs again and the procedure was repeated once. Data showed that predators consumed in both experimental periods nearly all prey in experiments with densities up to 40 eggs per arena and no mildew. However, the number of eggs consumed decreased more than twofold when mildew conidia were supplied, even at high prey densities. Differences in predation rate between treatments with and without mildew were highly significant. The results thus indicate that availability of mildew as an alternative food can reduce prey suppression byT. pyri. Possible implications of these findings in biological control of spider mites by generalist predatory mites are discussed. [ABSTRACT FROM AUTHOR]