Alternative food and biological control by generalist predatory mites: the case of Amblyseius swirskii.

Abstract

The use of predatory mites for the control of pests has a long history (Huffaker and Spitzer 1951; Huffaker and Kennett 1956; Fleschner 1959; Bravenboer and Dosse 1962), and started at a time when there was still doubt about the regulation of prey populations by predators (Huffaker and Kennett 1956). One of the first attempts of biological control with predatory mites was carried out in strawberry in California, USA, where the generalist predator Neoseiulus reticulatus was released to control cyclamen mites (Huffaker and Kennett 1953, 1956). Generalist predatory mites do not depend on the pest only, but can also use alternative food. It’s role in the persistence of predator populations at low pest densities was already acknowledged in these early studies: ‘‘A relatively high predator population usually is able to sustain itself for 2 months or more with very low populations of the cyclamen mite. When hungry, these predators have been observed to feed on honeydew, sugar solutions, egg yolk and other liquid foods.’’ (Huffaker and Kennett 1953). This ability to feed on alternative food was not always considered an advantage for biological control, but was taken as a sign of predators not being well adapted to the pest (Huffaker et al. 1969). Nevertheless, several of the early studies already showed that the presence of alternative prey for the predators did not negatively affect biological control, but rather improved it (Huffaker and Kennett 1956; Collyer 1964). Nevertheless, the emphasis in biological control of greenhouse pests has been on the use of specialist natural enemies for several decades (Encarsia formosa against greenhouse whitefly and Phytoseiulus persimilis against spider mites; Gould 1977). Perhaps this was caused by the long-standing conventional wisdom that biological control was most likely successful when using specialist natural enemies (Doutt and DeBach 1964; Murdoch et al.