Toxicity of Precocene-2 for the American Dog Tick, Dermacentor Variabilis (Acari: Ixodidae)1

Publisher Website
Google Scholar
Abstract
The plant derivative precocene-2 (2,6-dimethoxy-2,2-dimethyl chromene) was found to be toxic to immature Dermacentor variabilis ticks. Contact treatment with doses of 1.0 μg/cm2 was lethal for most unfed larvae and nymphs. When exposed to lesser doses, many more surviving larvae failed to feed than did untreated larvae or those exposed only to acetone. Contact treatment of engorged larvae resulted in ecdysial delay (0.015–0.50 μg/cm2), ecdysial mortality (0.50 μg/cm2), or death without molting (0.50 μg/cm2). Treatment of engorged nymphs resulted in ecdysial mortality without ecdysial postponement (1.0 μg/cm2) or induced a slow-death syndrome. In the latter case, adult characters developed normally but the treated nymphs failed to molt, and many remained in the nymphal skin for weeks or even months before eventual death. An inverse relationship was found between the developmental state of the immature ticks and their sensitivity to precocene-2. Nymphs were least sensitive to precocene-2 on the day of repletion. The LD50 for engorged nymphs, 0.87 μg/cm2, was only 2.1 × that for engorged larvae, 0.42 μg/cm2, even though the mean weight of an engorged nymph was more than 20 × that of an engorged larva. In contrast to the immature ticks, adults were relatively insensitive to precocene-2. Sex attractant activity was not inhibited, and insemination frequency only slightly inhibited by treatment with this compound. Feeding, and possibly oviposition, were impaired following topical treatment of partially fed females.

This publication has 1 reference indexed in Scilit: