We evaluated the toxicity of three insecticides (lambdacyhalothrin, spinosad, and S-1812) to the natural enemies Braconmellitor Say, Cardiochiles nigriceps Viereck,Coleomegilla maculata De Geer, Cotesiamarginiventris (Cresson), Geocoris punctipes (Say), andHippodamia convergens Guérin-Méneville, intopical, residual, and field assays. Lambda cyhalothrin exhibited thegreatest toxicity to the natural enemies. In topical toxicity tests,lambda cyhalothrin adversely affected each natural enemy speciesstudied. Residues of lambda cyhalothrin on cotton leaves were toxic toB. mellitor, C. nigriceps, C.maculata, and G. punctipes. Interestingly, residues ofthis insecticide were not very toxic to C. marginiventrisand H. convergens. Geocoris punctipes and C.maculata numbers in the field generally were significantly lowerfor lambda cyhalothrin treatments than for the other four treatments,substantiating the previous tests. Although cotton aphids began toincrease over all treatments around the middle of the test period, thenumber of cotton aphids in the lambda cyhalothrin plots wassignificantly higher than the number in any of the other treatments. Ascotton aphids increased in lambda cyhalothrin field plots, the predatorH. convergens also increased in number, indicating thatlambda cyhalothrin did not adversely affect it in accordance with theresidual tests. Spinosad exhibited marginal to excellent selectivity,but was highly toxic to each parasitoid species and G.punctipes in topical toxicity tests and to B. mellitorin residual tests. Spinosad generally did not affect the number ofG. punctipes, H. convergens, and C. maculata inthe field except for one day after the second application for G.punctipes. S-1812 exhibited good to excellent selectivity to thenatural enemies. Some reduction of G. punctipes occurred foronly a short period after the first and second application of thisinsecticide in the field. H. convergens and C.maculata were affected very little by S-1812.
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Vol. 93 • No. 6