Predatory arthropods and cues associated with predator presence elicit strong non‐consumptive effects on bluegrass billbugs

Abstract

AbstractTurfgrasses hosts a diverse community of predators that contribute to herbivore suppression. However, there is little evidence that predators directly consume a common turfgrass herbivore, the billbug (Sphenophorus sp.) (Coleoptera: Curculionidae). Given low rates of direct consumption by predators, prospects for strong non‐consumptive effects in billbugs were underappreciated. However, this assumed lack of non‐consumptive effects presupposes that herbivorous prey, like billbugs, can identify predators and the level of threat that they pose. Here, we examined this assumption and quantified the extent to which exposure to predators and predator cues altered the behavior (predator avoidance, feeding, and mating) of bluegrass billbug, Sphenophorus parvulus Gyllenhal. First, using a series of behavioral assays within microcosms, we exposed billbugs to predators – Pterostichus melanarius (Illiger) (Coleoptera: Carabidae), Harpalus sp. (Coleoptera: Carabidae), Philonthus sp. (Coleoptera: Staphylinidae), and Hogna sp. (Araneae: Lycosidae) – singly and in combination to measure the effect of contact with predators and potential synergy among predator species pairs. Indirect exposure to predators, predator odor, and non‐predatory arthropods were also used to measure effects of various predator cues on billbug behavior. In subsequent Y‐tube choice assays we determined whether billbugs discriminated between filtered air and predator odor to isolate chemical signaling as a potential mechanism for billbug predator detection. Direct exposure to predators increased billbug predator avoidance (up to 201%), and decreased billbug feeding (down to −78%), though no predation was observed. Similar behavioral changes were observed when billbugs were exposed indirectly to a predator, and to predator odor. In Y‐tube assays billbugs avoided predator odor, further suggesting billbugs use chemical cues to detect predator presence and that these may be a driver in their observed behavior. Our results show that billbugs exhibit strong non‐consumptive effects, even in the absence of strong direct consumptive effects. These results provide the foundation for further research concerning the role of chemical signaling in billbug predator detection.