Grafton-Cardwell, E.E., Striggow, R.A., & Ouyang, Y. 1996 Pesticide resistance in armoured scale influences citrus IPM in California.. Proceedings of the International Society of Citriculture I: 553-555.

Notes: [VIII International Citrus Congress, 12-17 May 1996, Sun City, South Africa.] Citrus thrips, Scirtothrips citri (Moulton), California red scale, Aonidiella aurantii, and yellow scale, A. citrina, are key pests of citrus in the San Joaquin Valley of California, USA. Biological control has historically not been sufficient to reduce these pests below economic thresholds in this region. Growers have relied heavily on organophosphate and carbamate insecticides to control citrus thrips and armoured scale. Laboratory bioassays of citrus thrips populations during the 1980s and armoured scale populations during the early 1990s indicate that resistance is developing in a portion of these populations, for the organophosphate and carbamate insecticides. The only alternative to these broad spectrum pesticides for armoured scale control is the use of narrow range petroleum oils and releases of the parasitoid Aphytis melinus. A. melinus are very sensitive to broad spectrum pesticides applied for control of citrus thrips and other pests. Thus, if A. melinus are used for scale control, control tactics for all of the pests must change from broad spectrum pesticides to selective pesticides, biological control, and other pest management techniques. Some years, despite our best efforts, the integrated pest management approach does not reduce key pests below economic thresholds. During these years, growers tend to shift back to broad spectrum pesticides. However, continued monitoring and detection of armoured scale resistance and slow registration of new pesticides are strong forces for change.