Genetic improvement of a parasitoid: response of Trioxys pallidus to laboratory selection with azinphosmethyl

Colonies of Trioxys pallidus Haliday (Hymenoptera: Aphidiidae) were collected from California walnut orchards during 1985-86 and screened for variability of responses to azinphosmethyl. Variability was found and laboratory selection was initiated with four colonies. All colonies responded to selection; after 7 to 12 selections, three colonies were combined (Select colony) and selection was conducted an additional 27 times. The coresponding base colonies were also combined and maintained for comparisons (Base). Concentration/mortality lines obtained for the Select and Base colonies after 5 and 27 selections, indicated 7and 9.2-fold differences in LC50 values, respectively. This selection response appeared inadequate to allow the resistant strain to survive field rates of azinphosmethyl, but when the resistant strain's survival was evaluated with several different bioassay methods, different conclusions were reached regarding the potential ability of the selected strain to survive field rates of azinphosmethyl.