Susceptibility of the Colorado Potato Beetle in Ontario to Insecticides12

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Abstract
First generation adults of strains of Leptinotarsa decemlineata (Say) collected from 4 locations in southwestern Ontario showed no evidence of resistance to azinphosmethyl, phosmet, methamidophos, carbaryl or carbofuran. Two of the 4 were resistant to endosulfan. Subsequent dosage-mortality studies using 3rd stage larvae of a susceptible and 1 endosulfan-resistant strain indicated the latter also was resistant to aldrin, endrin, and DDT. Relative susceptibility of larvae of the 2 strains to azinphosmethyl, chlorfenvinphos, carbaryl, and carbofuran was similar. Forty insecticides were screened against 3rd stage larvae and adults of the susceptible strain. Of materials presently recommended for use in Ontario carbofuran was the most effective larvicide > endosulfan > azinphosmethyl > carbaryl > phosmet > methamidophos. The experimental insecticides, Shell WL 41706 (alpha-Cyano-3-phenoxybenzyl 2, 2, 3, 3-tetramethylcyclopropane carboxylate), Shell WL 43775 (alpha-Cyano-3-phenoxybenzyl)-2-(4-chlorophenyl)-3-methyl-l-butyrate, chlorfenvinphos, and oxamyl were as or more effective than carbofuran or endosulfan. Endosulfan was the most toxic contact adulticide > carbofuran > azinphosmethyl > phosmet > carbaryl > methamidophos. WL 41706 and WL 43775 were more toxic than endosulfan.

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