Pesticide-Induced Hormoligosis of Citrus Thrips (Thysanoptera: Thripidae) Fecundity

The effects of four pesticides (dicofol, esfenvalerate, formetanate, and malathion) on the fecundity of citrus thrips, Scirtothrips citri (Moulton), were measured in laboratory trials with citrus leaves weathered in the field. Compared with oviposition on untreated leaves, fecundity increased significantly on leaves containing 21-d-old dicofol residues and 32-, 41-, and 64-d-old malathion residues. When citrus thrips females were exposed to various rates of 1-h-old leaf residues of dicofol, fluvalinate, formetanate, and malathion, fecundity was depressed at higher rates (1-25% mortality), elevated at intermediate rates (0.01-1% mortality), and was unchanged at lower rates. Because of potential insecticide-induced hormoligosis (stimulation), we urge caution in use of the insecticide check method in evaluating the effects of various natural enemies on arthropod pests and suggest that hormoligosis is an additional reason to avoid prophylactic treatment of citrus thrips.