Ehler, L.E., & Endicott, P.C. 1984 Effect of malathion-bait sprays on biological control of insect pests of olive, citrus, and walnut.. Hilgardia 52(5): 1-47.

Notes: The effect of malathion-bait sprays, directed against Mediterranean fruit fly (Ceratitis capitata (Wiedemann)), on biological control of selected non-target insects was investigated in northern California during 1982 and 1983. Following cessation of the spray program in one county, increases of olive scale (Parlatoria oleae (Colvee)) and black scale (Saisettia (Saissetia?) oleae (Olivier)) on olive and brown soft scale (Coccus hesperidum Linn.) and blacks cale on citrus were detected, compared to population levels of these scales in the adjacent unsprayed zone. The secondary outbreaks of these scales were attributed to destruction of natural enemies (chiefly parasites) by malathion. The outbreaks of black scale (citrus and olive) and brown soft scale were not apparent until one year after the first application of malathion-bait spray, or five months after the last application. Populations of cottony-cushion scale (Icerya purchasi Maskell), citrophilus mealybug (Pseudococcus calceolariae (Maskell)) and citricola scale (Coccus pseudomagnoliarum (Kuwana)) remained at low levels on citrus in the spray zone; no treatment effect on these species was detected. Latania scale (Hemiberlesia lataniae (Signoret)) on olive was apparently suppressed by the sprays. Walnut aphid (Chromaphis juglandicola (Kaltenbach)) in commercial walnut orchards was less abundant in the spray zone two months after the last application of malathion-bait; no suitable explanation for this was available. In Stockton, an outbreak of black scale on olive was detected shortly after the spray program ended, due to the destruction of natural enemies by malathion.