Interplanting Alfalfa as a Source of Metaseiulus occidentalis (Acari: Phytoseiidae) for Managing Spider Mites in Cotton

Cotton, Gossypium hirsutum L. (Malvaceae), plots were established in 1988 and 1989 with an alfalfa, Medicago sativa L. (Fabaceae), strip at one edge to determine whether alfalfa could serve as a source of the western predatory mite, Metaseiulus (= Typhlodromus = Galandromus) occidentalis Nesbitt (Acari: Phytoseiidae). Western predatory mites were released into the alfalfa early in the season. Spider mite (Acari: Tetranychidae) and western predatory mite density was monitored in alfalfa and in cotton at varying distances from alfalfa. Western predatory mite successfully established populations in alfalfa in both 1988 and 1989. Western predatory mite density was significantly higher close to alfalfa early in the season, indicating that alfalfa was the source. Average seasonal spider mite density was significantly lower close to the alfalfa. Spider mites were effectively controlled and cotton yield was higher adjacent to alfalfa in 1989 but not in 1988. Our results indicate that there is potential in the use of alfalfa as a nursery crop for enhancing western predatory mites in agricultural systems. (C) 1991 Academic Press, Inc.