Direct and indirect effects of four herbicides on the activity of carabid beetles (Coleoptera: Carabidae)

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Four herbicides—atrazine, simazine, paraquat, and glyphosate—were tested for their acute and chronic toxicity as well as repellent effects on five common carabid beetles (Amara sp., Agonum sp., Pterostichus sp., Anisodactylus sp., and Harpalus sp.) in laboratory and greenhouse experiments. These carabid species are potential biocontrol agents, and interference with their biology through herbicide applications, either directly or indirectly, could lead to soil pest outbreaks. Short-term field studies also were conducted to verify laboratory and greenhouse results. The four herbicides did not have significant acute or chronic effects on male or female carabid longevity or food consumption during one year after exposure to initial field-rate applications. Only simazine and atrazine had a repellent effect on carabids, an effect that lasted approximately three days in greenhouse studies. Behavioral studies indicate that once carabids, especially smaller ones (< 10 mm in length), establish burrows and foraging territories, they tend to remain in these areas and migrate out of them only slowly. There was no toxic or repellent effect of any herbicide in the field. Carabids, instead, apparently responded to the destruction of plant material which provided a less favorable habitat for the larger (> 10 mm length) carabids. Glyphosate and paraquat had the greatest effect on carabids by the second week in field studies, with significantly fewer large carabids found in these two treatments than in the control. Large carabids did not return to paraquat- and glyphosate-treated field areas until approximately 28 days after application; consequently, lower rates of predation of early-season lepidopteran pests by these carabid species may occur in no-tillage corn fields that utilize herbicides for weed control.

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ELECTRONIC FILE - Zoology