Field releases of the predatory mite Neoseiulus fallacis (Acari : Phytoseiidae) in Canada, monitored by pyrethroid resistance and allozyme markers

The predacious phytoseiid mite Neoseiulus fallacis (Garman) is an important agent for the biological control of spider mites in deciduous fruit orchar ds in North America and Canada. It would be helpful to monitor the fate of released individuals to improve the results of introductions of the predato rs in biological control trials. We have used two types of genetic markers, pyrethroid resistance and allozymes, for indirect estimation of the surviv al of N. fallacis introduced in an apple orchard in Ontario, Canada. Mite s amples were submitted to toxicological tests. The polymorphism of four enzy mes was studied in individual females using an isoelectric focusing techniq ue. A mite sample was taken from the field, mass-reared in the laboratory, and selected for permethrin resistance. This strain was released on several apple trees treated with permethrin, and mite samples were collected from the same trees 10 to 90 days later. The genetic composition and the insecti cide resistance level of this sample were compared to those of two other sa mples from trees where mites had not previously been released, either in th e same orchard or in a neighboring block. A control susceptible strain was compared using mites collected earlier from trees on the same site but outs ide the present experiment. The mites collected from the release trees and those from the strain used for the releases were found to be genetically cl osely related, as judged from a small genetic distance, and from similar le vels of insecticide resistance in both samples. The control samples from th e nonrelease trees were genetically distant from these and displayed low re sistance levels. These results indicate that the released genotypes establi shed and persisted in the release trees for the period of the experiment. T he utility of the two approaches in assessing the fate of released natural enemies is discussed. (C) 2001 Academic Press.