Vienna-8 sterile males are currently released in Spain to reduce wild populations of the medfly. Because pesticides are required to maintain populations of some citrus key pests below economic thresholds, there is a need to evaluate the effects of pesticides commonly used in citrus on Vienna-8 males. Males were exposed to differently aged residues of eight pesticides. Abamectin, etofenprox, etoxazole, petroleum spray oil, pymetrozine, and pyriproxyfen resulted harmless to Vienna-8 males. However, fresh residues of chlorpyrifos and spinosad caused high mortalities and had residual effects until 21 and 28 d after treatment, respectively. Following the same method, the lethal effects of chlorpyrifos and spinosad on Ceratitis capitata (Wiedemann) wild-type (wt) males were determined. Surprisingly, these pesticides resulted more toxic for wt than for Vienna-8 males. To determine whether these results could be attributed to intrinsic characteristics of the pesticides or to behavioral differences among Vienna-8 and wt males, a topical application trial was conducted. Vienna-8 males were twice as susceptible to chlorpyrifos as wt males, whereas their susceptibility to spinosad was slightly lower. These results in intrinsic toxicity did not directly explain the differences observed in the extended-laboratory tests with these pesticides. We hypothesize that the lower flight activity of Vienna-8 males relative to wt conspecifics can explain the lower risk observed for Vienna-8 males in the residual tests. Our results should be taken into account when planning area-wide Sterile Insect Technique programs against C. capitata especially in those areas where treatments with chlorpyrifos are approved.
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Vol. 106 • No. 3