Comparison of the responses of two predaceous mites, Typhlodromus pyri and Zetzellia mali, to variation in prey density

Abstract

The ability of a predator to respond to prey density in a patchy habitat has been the focus of much study in biological control systems and elsewhere. Here we look at the response of two species of predatory mite commonly found in commercial apple orchards, Typhlodromus pyri Scheuten and Zetzellia mali Ewing. The two species differ in several characteristics: T. pyri is a more successful biological control agent, is more mobile, has a slightly narrower breadth of diet and prefers the target prey, Panonychus ulmi Koch. We measured resisdence time as a function of prey density, both under field and laboratory conditions. Both predators showed a wide variation in behaviour; however, Z. mali increased residence time in response to the presence of prey, while T. pyri did not show a significant response. Both predators usually left a patch before all prey were consumed. Patterns from the field and laboratory were similar, although residence time was shorter under field conditions.