Resistance of Aonidiella aurantii and A. citrina to organophosphates and carbamates
In California (US), citrus growers have mainly used organophosphorous and carbamate insecticides for scale insect control. Aonidiella aurantii (EU Annex II/A1) and A. citrina are key pests in the San Joaquin Valley orchards. When organophosphorous insecticides first came into use, growers were able to maintain economic control of armoured scales with one spray application of parathion every 2-3 years. More recently, growers observed that these insects are becoming increasingly difficult to control. Citrus fruit infested with these two scale species were collected from 68 orchards in four counties of the San Joaquin Valley over three seasons to test for insecticide resistance. Results of laboratory tests suggest that resistance to organophosphorous compounds (chlorpyrifos and methidathion) is developing in Aonidiella aurantii and A. citrina in this region of California. Resistance to carbamate insecticide (carbaryl) appears less intense. The authors stressed the need for better management programmes. Traps could be used to monitor these pests so that insecticides are applied only when scale populations are above the established economic threshold. Organophosphorous and carbamate insecticides should be used in rotation with petroleum oils to delay the appearance of resistance. And in places where resistance have appeared, growers should replace the application of organophosphorous and carbamate insecticides by biological control. The use of parasitoids (Aphytis spp. and Comperiella spp.) can be combined with the more selective petroleum oil sprays.
Sources
Grafton-Cardwell, E.E.; Vehrs, S.L.C. (1995) Monitoring for organophosphate- and carbamate- resistant armored scale (Homoptera: Diaspidideae) in San Joaquin Valley citrus.
Journal of Economic Entomology, 88(3), 495-504.