MONITORING FOR ORGANOPHOSPHATE-RESISTANT AND CARBAMATE-RESISTANT ARMORED SCALE (HOMOPTERA, DIASPIDIDAE) IN SAN-JOAQUIN VALLEY CITRUS

Citrus fruits infested with California red scale, Aonidiella aurantii (Maskell), and yellow scale, A. citrina (Coquillett), were collected from a total of 68 orchards in four counties in the San Joaquin Valley of California over three seasons to test for insecticide resistance. California red scale populations were collected from Madera, Fresno, Tulare, and Kern counties. Yellow scale populations were fewer in number and were found only in Tulare County. The results of laboratory bioassays of the infested fruit suggest that resistances to the organophosphate insecticides chlorpyrifos and methidathion are developing in the two armored scale species in this region. Armored scale resistance to the carbamate insecticide, carbaryl, appears to be less intense than for the organophosphates at this time. The populations showing the lowest percentage of mortality to any of the tested insecticides were located in eastern Tulare and Kern counties. An insecticide resistance management strategy for this citrus growing region is discussed.