Tasty on the outside, but toxic in the middle: grasshopper regurgitation and host plant-mediated toxicity to a vertebrate predator

Abstract

Regurgitation by arthropods is often considered to be a rudimentary form of defense against predators. In phytophagous insects, regurgitate composition will vary with diet, and plant secondary compounds from host plants can contribute to the effectiveness of regurgitate deterrence. Regurgitation in response to predator attack is particularly common in grasshoppers. However, there is little empirical evidence in favor of grasshopper regurgitation as an effective antipredator mechanism in natural predator-prey systems. In particular, studies of the effect of grasshopper diet on regurgitate deterrence to vertebrate predators are lacking. This study investigated the relationship between diet and predator defense in the grasshopper, Schistocerca emarginata (=lineata) (Orthoptera: Acrididae). Using the insectivorous lizard, Anolis carolinensis (Iguanidae), as a predator, I demonstrate that consumption of Ptelea trifoliata (Rutaceae) by S. emarginata can confer distastefulness as well as toxicity. Regurgitate deterrence is mediated strictly by host plant material in the gut and does not require an enteric contribution from the grasshopper. Regurgitation by Ptelea-fed S. emarginata can result in rejection prior to ingestion by A. carolinensis and can enable grasshoppers to survive predator attacks.