Rosenheim, J.A. 1987 . Genetic Improvement of a Biological Control Agent: Evolution of Pesticide Resistance in Aphytis melinus DeBach (Hymenoptera: Aphelinidae) ... University of California, Berkeley 171 pp.

Notes: [Title continues: through Natural and Artificial Selection. Ph.D. Thesis, Marjorie Hoy, Advisor.] Thirteen populations of Aphytis melinus DeBach, a key biological control agent of California red scale, Aonidiella aurantii (Maskell), were collected from the citrus-growing regions of California. Each population's history of exposure to insecticides was estimated by determining history of insecticide use at both local (in-grove) and regional (county-wide) geographical scales. Concentration/mortality regressions for five insecticides widely used in citrus (carbaryl, chlorpyrifos, dimethoate, malathion, and methidathion) were estimated for the populations. LC50's were correlated with both in-grove and county-wide pesticide use histories; patterns of variability were best explained by results of a multiple regression analysis that combined the influences of these two histories. Roles of food limitation, migration, and host distribution in determining patterns and rates of evolution of pesticide resistance in arthropod biological control agents are discussed. Sublethal effects of citrus insecticides on A. melinus were investigated. Longevity, daily rate of progeny production per female, and size and sex ratio of offspring were measured for parasitoids exposed to rates near the LC50's of carbaryl, chlorpyrifos, dimethoate, malathion, and methidathion. Survivors of the carbaryl exposure exhibited no significant sublethal effects. Each of the organophosphorous materials reduced longevity by 73-85% and temporarily depressed progeny production. Populations of A. melinus were artificially selected for increased tolerance to the same five insecticides. Selection produced gradual, small to moderate increases in resistance, accompanied in three of 12 selected lines with apparent decreases in genetic variation for pesticide tolerance. Bioassay techniques using one or two treated leaf surfaces for assessing toxicity of field-weathered pesticide residues were used to determine the survival of the carbaryl resistant strain on field rates of carbaryl. The two-leaf bioassays of carbaryl residues revealed that the carbaryl resistant strain exhibited $>$50% survival as early as 18 days post-treatment, while the base colony continued to suffer $>$86% mortality on 75-day-old residues, the oldest tested. Because larval A. melinus are shielded from insecticides by the bodies of their scale insect hosts, this selected increase in carbaryl tolerance of adults may enable A. melinus to persist in carbaryl-treated groves.