Main content area

Release, dispersal, and recovery of a laboratory-selected strain of the walnut aphid parasite Trioxys pallidus (Hymenoptera: Aphidiidae) resistant to azinphosmethyl

Hoy, M.A., Cave, F.E., Beede, R.H., Grant, J., Krueger, W.H., Olson, W.H., Spollen, K.M., Barnett, W.W., Hendricks, L.C.
Journal of economic entomology 1990 v.83 no.1 pp. 89-96
Juglans, orchards, varieties, Chromaphis juglandicola, biological control, Trioxys pallidus, strains, insecticide resistance, azinphos-methyl, mortality, parasites, California
A strain of Trioxys pallidus Haliday, selected in the laboratory for resistance to azinphosmethyl, was mass reared and released into five commercial walnut blocks in California to determine whether the strain could survive field applications of azinphosmethyl or methidathion, persist, and parasitize the walnut aphid, Chromaphis juglandicola Kaltenbach. Approximately 75,000 parasites were reared on potted walnut trees in a University of California greenhouse in Berkeley; releases were made after azinphosmethyl applications in three sites, after methidathion application in one site, and just before a methidathion application in one site. Colonies of T. pallidus collected from each orchard before the releases were tested with a discriminating dose of azinphosmethyl to estimate resistance levels of the wild population. Samples of T. pallidus were collected once or twice from each block after releases were made and from adjacent walnut blocks in two sites. The samples were then tested with azinphosmethyl. The high survival rates of the parasites indicated that the strain of T. pallidus resistant to azinphosmethyl established and persisted through the growing season in four of the five walnut blocks and dispersed to nearby nonrelease blocks in two of two sites sampled. Counts of aphids and mummies support the conclusion that the laboratory-selected strain survived applications of azinphosmethyl or methidathion, parasitized aphids, and persisted within the release and nearby nonrelease sites during the 1988 growing season.