The effect of herbicide on activity level and chemically-mediated antipredator responses in wolf spiders

Spiderlings of the wolf spider Rabidosa rabida show innate effective antipredator responses (freezing) in the presence of silk and excreta cues of the syntopic intraguild predatory spider, Pardosa milvina. Both species are commonly found in agricultural systems where herbicides may interfere with predator-prey dynamics within these species. Published studies indicate that a variety of environmental factors may degrade or modify spider silk and therefore could potentially influence the ability of predator cues to inform antipredator decisions in prey spiders. Some herbicides may act as a stimulant and increase the activity level of wolf spiders. We tested the effect of dicamba on three aspects of Rabidosa and Pardosa behavior. We measured the effect of spraying dicamba on the ability of Rabidosa spiderlings to detect silk and excreta cues from Pardosa. We also tested if dicamba sprayed before or after Pardosa silk deposition influenced freezing responses and subsequent predation in Rabidosa when paired with a live Pardosa predator. In a second experiment we measured both activity level and predation frequency of Pardosa on Rabidosa when Pardosa, Rabidosa, or both spiders were chronically exposed to herbicide-treated soils over a one-week period. Dicamba sprayed on substrates with predator cues from Pardosa did not significantly influence Rabidosa survival or Pardosa attack latency when Rabidosa wasn’t previously exposed to predator cues; however, Rabidosa and Pardosa both increased activity level when exposed for one week to dicamba substrates. We also found significant differences in Rabidosa survival with a live Pardosa when exposed for at least 24 hours with predator cues depending on if the predator and/or prey was exposed to dicamba. Our findings suggest that dicamba may mediate silk-cued predator-prey interactions in these species particularly when the prey have been previously primed with predator silk cue