Use of genetic improvement in biological control

Abstract

Genetic improvement is an ancient concept that has been applied to silkworms and honey bees. Improvement of biological control agents has been discussed but fears of laboratory deterioration and inadvertent selection of the laboratory-selected biological control agent restricted interest in this potential tool. A case of field efficacy in a biological control agent that had undergone laboratory selections is described. The phytoseiid mite Metaseiulus occidentalis (Nesbitt) is the most important predator of spider mites in deciduous orchards and vineyards in western North America. It acquired resistance to organophosphorus (OP) insecticides and sulfur through field selection. Strains resistant to carbaryl-OP and permethrin-OP pesticides were obtained through laboratory selection and crosses. The genetics of these resistances are known and all, except for permethrin resistance, are determined by major semi-dominant genes. Permethrin resistance is polygenically determined. Laboratory-selected predator strains established, survived relevant pesticides in the field, multiplied, dispersed, overwintered, and had a measurable impact on spider mites in small plots in apple, pear, and almond orchards in California, Washington, and Oregon. During 1981, carbaryl-OP and permethrin-OP resistant M. occidentalis were released into commercial almond orchards in the San Joaquin Valley of California. Two massproduction schemes, and several release methods were tested. Orchards were monitored in 1982 to determine if the released predators were effective in controlling spider mites, and whether acaricide usage could be reduced or eliminated. Permanent establishment of these genetically improved predators in commercial orchards is the goal. Genetic improvement of biological control agents is time consuming, expensive compared to classical importation, and requires substantial knowledge. It may be useful, in particular, for natural enemies of pests which are widely distributed, or for inundative releases into greenhouses. Biological control agents other than phytoseiids and traits in addition to pesticide resistance should be considered for genetic improvement.