The benzoylphenyl urea insect growth regulators (IGRs), diflubenzuron, alsyston, CGA 112913, UC 62644 and Thuringiensin, were tested on adult and late third instar Trioxys pallidus and first instar walnut aphids. The organophosphates, phosalone and azinphosmethyl were used as positive controls. The IGRs and Thuringiensin were not acutely toxic to adult and larval Trioxys when contact, topical a...

During the past year, we reared and released approximately 40,000 parasites of the Guthion-resistant strain of walnut aphid parasite, Trioxys pallidus, into a walnut orchard near Red Bluff, CA. Parasites were recovered three times during the season following release and results of bioassays indicate the resistant strain has established and persisted through its first field season in this orchar...

During the past year, we collected walnut aphid parasitoids, !. pallidus, from 8 walnut orchards. Parasites from 2 sites were maintained as individual colonies, those from'the six other sites were pooled into one colony. These colonies and one started in 1985 from three sites were screened with Guthion. We found substantial variability in responses to Guthion by these colonies, which suggests t...

Genetic selection for resistance to pesticides has been proposed as a method for enhancing the use of parasites in integrated pest management (IPM)programs. Genetic improvementof parasites is an experimental tactic in biologicalcontrol, and a series of questions need to be resolved. First, is it possible to select parasites for resistance to pesticides? The JulyAugust 1988 issue of California A...

Homogeneity in azinphosmethyl resistance was assessed in males of a laboratory-selected (Select-H) and susceptible (Yolo) colony of Trioxys pallidus (Hymenoptera: Aphidiidae) using a time response assay. No evidence of heterogeneity within the two colonies was found. Reciprocal crosses between the Yolo and Select-19 colonies resulted in F1 females which exhibited a semidominant response to azin...

During the past year, we evaluated the fitness and likelihood of establishing the Guthion-resistant strain of walnut aphid parasite, Trioxys pallidus, in California walnut orchards by conducting a combination of laboratory and field experiments. We compared the stability of the azinphosmethyl resistance in the resistant strain and in progeny derived from crossing the resistant and the base colo...

The Guthion-resistant strain of walnut aphid parasite, Trio x y s p a II i d us. was mass reared in the greenhouse on potted walnut trees and released into five commercial walnut blocks near Colusa, Stockton, Modesto, and Hanford. Parasites successfully established in four of the five sites, surviving on field rates of Guthion and Supracide. The Guthion-resistant strain persisted in the release...

Coevolution may be an important component of the sustainability of importation biological control, but how frequently introduced natural enemies coevolve with their target pests is unclear. Here we explore whether comparative population genetics of the invasive walnut aphid, Chromaphis juglandicola, and its introduced parasitoid, Trioxys pallidus, provide insights into the localized breakdown o...