Effects of the pyrethroid insecticide Cypermethrin on the locomotor activity of the wolf spider Pardosa amentata: quantitative analysis employing computer-automated video tracking

Abstract

Wildlife in areas surrounding arable land is almost inevitably exposed to pesticide spray. Even at doses far below the lethal level, this presents a threat to vulnerable species. The widely used pyrethroid insecticides, including Cypermethrin, are known for their direct effect on the locomotor apparatus of animals, inducing varying degrees of paresis. Quantitative measurements of the voluntary locomotion of animals express an integrated response to changes in biochemical and physiological processes. In the present study, the effect of Cypermethrin on the voluntary locomotion of the wolf spider Pardosa amentata was quantified in an open field setup, using computer-automated video tracking. Each spider was recorded for 24 hr prior to pesticide exposure. After topical application of 4.6 ng of Cypermethrin, the animal was recorded for a further 48 hr. Finally, after 9 days of recovery, the spider was tracked for 24 hr. Initially, Cypermethrin induced an almost instant paralysis of the hind legs and a lack of coordination in movement seen in the jagged and circular track appearance. This phase culminated in total quiescence, lasting approximately 12 hr in males and 24-48 hr in females. Following paresis, the effects of Cypermethrin were evident in reduced path length, average velocity, and maximum velocity and an increase in the time spent in quiescence. Also, the pyrethroid disrupted the consistent distributions of walking velocity and periods of quiescence seen prior to pesticide application. Our results suggest that normal locomotion had returned 9 days after Cypermethrin application, but that recovery of high velocities was still incomplete.