Prey use an array of defenses to reduce their predation risk. Herbivores that feed on toxic food plants often sequester harmful compounds for use as a constitutive chemical defense against predators. Such chemically-defended prey are often brightly colored (aposematic) to warn predators of their toxicity. Caterpillars of the monarch butterfly, Danaus plexippus, are well-known for their aposematic coloration. They feed on milkweed (Asclepiadaceae) host plants and sequester toxic cardenolides from the plant in their bodies. While this strategy provides an effective defense against most predators, the Chinese mantid Tenodera sinensis consumes D. plexippus caterpillars in the field without any apparent ill effects. This behavior is surprising since naïve T. sinensis that consume milkweed bugs (Oncopeltus fasciatus) vomit after consumption and subsequently refuse to attack these insects. We conducted research exploring how these mantids are capable of consuming ‘toxic’ D. plexippus caterpillars. We conducted a series of video-recorded behavioral trials observing T. sinensis predation of D. plexippus larvae and caterpillars of two ‘non-toxic’ lepidopterans (the European corn borer, Ostrinia nubilalis, and wax worms, Galleria mellonella). In addition to taking behavioral data, we also determined prey consumption rates and the percentage of the total prey body mass discarded by the mantid.
Results/Conclusions
We observed a total of 44 predator prey encounters between adult T. sinensis and the three species of tested prey. Mantids encountering D. plexippus caterpillars exhibited a very distinct series of behaviors. While holding the caterpillars with their raptorial forelegs, the mantids used their mouthparts to cut the caterpillar open in order to allow the gut to fall out before consuming the remainder of the carcass. The mantid showed no interest in, and never attempted to consume, the discarded material. This ‘gutting’ behavior was never observed when mantids consumed non-toxic O. nubilalis or G. mellonella caterpillars (Χ2=42.3, p<0.001); mantids ate the entire carcass. The gutting behavior resulted in differences in the mean percent prey mass discarded by the mantids (F2,31=25.1, p<0.001). Mantids discarded 41+3.1% of the mass of D. plexippus caterpillars, a much larger fraction than for either O. nubilalis (14+4.6%, an amount that consisted entirely of hemolymph) or G. mellonella (0%). Despite these differences, mantid consumption rates (g prey min-1) for all three prey species were similar (F2,31=0.25, p=0.78) suggesting minimal costs associated with the gutting behavior.