High Sensitivity of the Tiger Beetle, Cicindela circumpicta, to Toxicity from Pyrethroids and Neonicotinoids, and Implications for Ecosystem Function and Species Extinctions

Abstract

Risks to non-target species from pesticides have been a concern since the 1960s, but non-target arthropods have never received the attention as have non-target vertebrate species. Pesticide exposure could be a contributing factor in the decline of the endangered Cicindela nevadica lincolniana, as well as declines in predaceous and pollinating insects. Consequently, we examined susceptibility to three common pesticides (glyphosate, bifenthrin, and imidacloprid) of larvae of Cicindela circumpicta, a co-occurring species with Cicindela nevadica lincolniana and a potential model species for insect predators generally. Toxicity was tested by direct, 24-h exposure by contact to larvae. No toxicity from glyphosate was observed at any of the doses tested, nor was death in any controls observed. In contrast, C. circumpicta showed alarmingly high sensitivity to small amounts of both imidacloprid and bifenthrin, two of the most widely used insecticides worldwide. This level of toxicity shows a 3-fold higher sensitivity than reported for insect pollinators. The high sensitivity of tiger beetles to neonicotinoids, and the wide and continual use of this pesticide, strongly indicates the potential for declines in larval insect predators generally, and with the decline of C. n. lincolniana specifically. Results suggest that the focus of the concern for non-target impacts from neonicotinoids should be expanded for insect natural enemies.