Effects of Insecticides on Biological Control of Insect Pests of Citrus1

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Abstract
Increase in cottony-cushion scale after DDT treatment is caused by a differential toxicity to the scale and its predator vedalia. The "trap effect" of DDT-treated area on an adjoining untreated area in decreasing the effectiveness of vedalia against cottony cushion scale has been demonstrated. Increase of citrus red mite after applications of DDT, cryolite, and zinc sulfate is related to the deleterious effects of these materials upon predators. Specificity of various insecticides to citrus red mite predators has been shown, with change-overs in dominance of spp. of the natural-enemy complex resulting from DDT treatments. Increase in populations of long-tailed mealybug was induced by applications of chlordane, cryolite, zinc sulfate, bis-(p-chlorophenoxy)-methane, talc, and light dosages of DDT. The upset of natural control of California red scale was demonstrated where a selective advantage was given the host over the parasite by light DDT dosages.