Effect of malathion-bait sprays on biological control of insect pests of olive, citrus and walnut.

Abstract

The effect of malathion-bait sprays, directed against Mediterranean fruit fly Ceratitis capitata on biological control of selected non-target insects was investigated in northern California. Following cessation of the spray program, increases of olive scale Parlatoria oleae and black scale Saisettia oleae on olive and of brown soft scale Coccus hesperidium and black scale on citrus were detected. The secondary outbreaks of these scales were attributed to destruction of natural enemies (chiefly parasites) by malathion. Populations of cottony-cushion scale Icerya purchasi, citrophilus mealybug Pseudococcus calceolariae and citricola scale Coccus pseudomagnoliarum remained at low levels on citrus in the spray zone; no treatment effect on these species was detected. Latania scale Hemeberlesia lataniae on olive was apparently suppressed by the sprays. Walnut aphid Chromaphis juglandicola in commercial walnut orchards was less abundant in the spray zone 2 months after the last application of malathion-bait. Future (medfly) eradication programs which employ numerous sequential applications of malathion-bait spray can be expected to disrupt a substantial portion of the biological control which exists in the target zone.-from Authors