Persistence of Typhlodromus pyri and Metaseiulus occidentalis (Acari: Phytoseiidae) on apple after inoculative release and competition with Zetzellia mali (Acari: Stigmaeidae)

Biological control of European red mite Panonychus ulmi and apple rust mite Aculus schlechtendali varied in 1991 in 20 prey-predator treatment plots after single and mixed releases of Metaseiulus occidentalis and Typhlodromus pyri were made in 1990. Control of spider mites in 1991 was better in mixed-species than in single-species release plots. In fall, eggs of M. occidentalis disappeared before eggs of T. pyri did. In spring, eggs of T. pyri appeared first. Oviposition by M. occidentalis may have been slowed by cool weather and limited use of pollen as food. With few prey present, competition favored T. pyri, and M. occidentalis eventually disappeared from mixed-, but not from single-species plots. M. occidentalis was more affected by Zetzelia mali than was T. pyri, but T. pyri had more impact on populations of this stigmaeid mite. The two phytoseiids have complementary traits that allow them to control pest mites together, but their management may be complicated by interspecific competition. -from Authors