Lethal and sublethal effects of selected insecticides on commercially available natural enemies of whiteflies


Abstract: Whitefly natural enemies are commonly used to control infestations, especially aspart of Integrated Pest Management schemes. The efficacy of beneficial arthropods asbiological control agents, however, may be compromised by lethal or sublethal side-effectscaused by insecticides. This study evaluated such side-effects of a range of insecticides usedin whiteflies control on three widely employed natural enemies of Bemisia tabaci andTrialeurodes vaporariorum: the parasitoid Eretmocerus eremicus, the predatory bugNesidiocoris tenuis and the predatory mite Amblyseius swirskii. Insecticide-induced mortalitywas evaluated by exposing E. eremicus adults and N. tenuis adults and pupae to treatedsurfaces and by directly applying insecticide on A. swirskii adults and E. eremicus pupae.Acetamiprid was the most toxic of the formulations, for each of the species tested, causing78.3% and 51.6% mortality to E. eremicus pupae and adults, 54.5% mortality to A. swirskiiadults, and 97.9% and 100.0% mortality to N. tenuis nymphs and adults, respectively.Pymetrozine caused 25.8% and 40.0% mortality to E. eremicus pupae and adults, while it didnot affect the survival of A. swirskii. Pyriproxyfen-induced mortality was 17.1% for E.eremicus pupae, 11.1% for A. swirskii adults and 45.8% for N. tenuis nymphs, while thesurvival of E. eremicus and N. tenuis adults was not reduced. Spiromesifen was toxic to N.tenuis (54.2% and 42.1% mortality in nymphs and adults), but not to E. eremicus or A.swirskii. Spirotetramat did not reduce the survival of N. tenuis or A. swirskii. Besidesmortality, sublethal effects of some of the insecticides were also evaluated, by comparingfeeding rate (whitefly eggs consumed per day) in insecticide-treated and control A. swirskiiand N. tenuis and fecundity in A. swirskii. Acetamiprid reduced A. swirskii fecundity by56.6% and pyriproxyfen by 50.5%, while pymetrozine and spiromesifen did not have aneffect. The feeding rate of A. swirskii was reduced by 42.6 and 30.7% by pymetrozine andpyriproxyfen, respectively, while that of N. tenuis was reduced by 35.1% by pymetrozine andwas not affected by pyriproxyfen. Overall, while acetamiprid was generally the most toxic toeach of the species in the study, most insecticides used were only toxic to some of the species/stages. Also, insecticides that did not cause significant mortalities, did have significant sublethal effects.

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