TOXICITY OF ALIPHATIC AND AROMATIC ISOTHIOCYANATES TO EGGS OF THE BLACK VINE WEEVIL (COLEOPTERA, CURCULIONIDAE)

Plant-derived isothiocyanates are rode to a number of soil organisms; however, the differential toxicity of various isothiocyanates to many soil-borne plant pests has not been determined. We tested the contact toxicity of methyl, propyl, allyl, phenyl, benzyl, and 2-phenylethyl i sothiocyanates to eggs of the black vine weevil, Otiorhynchus sulcatus (F.). Eggs were collected every 2 d from a colony of field-collected w eevils and preconditioned over a 5-d period. To reduce the variability of responses, only eggs with melanized chorions were used for all bio assays. Eggs were clipped into acetone solutions of isothiocyanates fo r 2 min. Controls were treated with acetone alone. Treated eggs were i ncubated for 14 d at 24 +/- 2 degrees C and 100% RH. Mortality respons e curves of black vine weevil eggs were analyzed using probit analysis . AU isothiocyanates tested were toxic to weevil eggs; however, isothi ocyanates containing an aromatic moiety (phenyl, benzyl, and e-phenyle thyl) were considerably more toxic than aliphatic (methyl, propyl, and allyl) isothiocyanates. Average mortality in acetone-treated controls was <6%. These results suggest that soil amendments of Brassica aroma tic isothiocyanates may have greater insecticidal potential than those producing aliphatic isothiocyanates.