How glyphosate altered the behaviour of agrobiont spiders (Araneae: Lycosidae) and beetles (Coleoptera: Carabidae)

Abstract

Cultivation of herbicide-tolerant strain of GM corn involves applications of a non-selective herbicide. Mortality of arthropod natural enemies resulting from the application of herbicides is negligible. But nothing is known how herbicides affect the behaviour of natural enemies and thus alter their pest control efficacy. Aim of the study was to assess the effect of the Roundup residues on the predatory, defensive, locomotory and reproductive behaviour of epigeic spiders and carabid beetles. Specimens of Pardosa agricola (Araneae: Lycosidae) and Poecilus cupreus (Coleoptera: Carabidae) were exposed for 2h to the fresh and 1-day old residues of Roundup Biaktiv (Monsanto, IPA 480g/l). Predation rate was similar for all treatments in both spiders and beetles. Spiders did not avoid surface treated with herbicide residues more than the control surface, but beetles slightly avoided surface with fresh residues. The speed of locomotion of spiders was not altered by herbicide residues, but beetles exposed to residues crawled at significantly lower speed than the control group. Herbicide residues did not affect the escape efficacy of spiders from a predator. Residues had no detrimental effect on the courtship, mating frequency and duration in spiders. Roundup Bioaktiv thus appears to be harmless to lycosid spiders and only slightly harmful to carabid beetles. The biological control potential of both predators should not be reduced by the application of Roundup Bioaktiv.