Penetration of pesticides into the bulb miteRhizoglyphus echinopus (Acari: Acaridae)

Bulb mites,Rhizoglyphus echinopus (Fumoze and Robin), were exposed for 10 min in vials precoated with 23 radiocarbon-labeled pesticides, and the kinetics of penetration were assessed following post-exposure periods of 320 min or 24h, depending upon the compound. With all pesticides, penetration was biphasic and consisted of a rapid initial component (alpha phase) followed by a much slower secondary component. The alpha phase of penetration was analyzed with a linear model, and the entire penetration curve was analyzed with a non-linear model. Correlation analyses of ten mass balance and penetration parameters and partition coefficients yielded 14 combinations that were significant atP<0.05. It was found that compounds with the fastest penetration rates had the highest dosing coefficients and the lowest octanol-water partition coefficients. Thus, fastest penetration was associated with relatively polar compounds such as oxythioquinox, promecarb, methomyl, aldicarb, and chlordimeform, whereas slowest penetration was observed with lipophilic compounds such as DDT, diflubenzuron, di-2-ethylhexyl phthalate, and the pyrethroids. However, the polar formetanate hydrochloride penetrated very slowly and was an exception to this generalization. These results provide a basis for suggesting that pesticide penetration proceeded at a faster rate in bulb mites than in two-spotted spider mites,Tetranychus urticae Koch, in other studies.