In agroecosystems, arthropod predators are frequently exposed to anthropogenic chemicals such as glyphosate, the active ingredient in many commonly-used herbicides (e.g. Round-Up®). Previous research has shown Pardosa milvina, a numerically dominant wolf spider in agroecosystems, to move faster but spend less time moving and move shorter distances under exposure to herbicide. This study aimed to 1) isolate the effects of a glyphosate-based herbicide on the activity of two other agrobiont arthropod predators whose interaction with P. milvina coincides seasonally with herbicide application, and 2) assess the effects of this herbicide on the behavioral response of P. milvina to the cues of two other predators within its guild. In the first study, we exposed another wolf spider species, Hogna helluo, and a species of ground beetle, Scarites quadriceps, to the herbicide Buccaneer Ultra® via a topically placed droplet and residually via substrate. In the second study, we tested the effects of chemical cues from H. helluo and S. quadriceps and exposure to herbicide on the activity, emigration, and survival of P. milvina using full-factorial laboratory experiments. We used an automated tracking system (Videomex-V) to monitor locomotion and quantify associated behaviors.
Both H. helluo and S. quadriceps increased non-forward activity under exposure to herbicide. Both predator cues and herbicide led to a decrease in movement by P. milvina. However, although H. helluo cues alone decreased movement, S. quadriceps cues only decreased movement when combined with herbicide. Our results suggest that glyphosate-based herbicides affect interactions between arthropod predators, which in turn may alter their effectiveness as biocontrol agents.