Avoidance of prey toxicity by the Chinese mantid, Tenodera sinensis

Monarch caterpillars, Danaus plexippus, feed on milkweed host plants (Asclepiadaceae) 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, has been observed to consume monarch caterpillars in the field without any apparent ill effects.  This behavior is of interest since naïve mantids that consume milkweed bugs vomit after consumption and subsequently refuse to consume these insects.  We have begun to study how these mantids consume ‘toxic’ monarch caterpillars without harming themselves.  We conducted a series of behavioral trials observing mantid predator-prey encounters with monarch caterpillars and ‘non-toxic’ larvae of European corn borers, Ostrinia nubilalis, and wax worms, Galleria mellonella.  We also determined consumption rates and percent prey body mass discarded by the mantid. 

We found that Chinese mantids gut monarch caterpillars, allowing the gut content to fall from the prey without any further intent to consume it, but never gut either of the non-toxic caterpillars (wax worms or European corn borers).  Consumption rates (g prey eaten min^-1) for all three prey species was similar suggesting minimal costs associated with the gutting behavior.  Mantids discarded a larger portion of monarch caterpillar mass than of either non-toxic prey.

The fact that the mantids consumed the gutted monarch caterpillars without any ill effects suggests that plant-derived cardenolides are concentrated in the monarch caterpillar’s gut. We plan on testing this hypothesis by using HPLC to assess cardenolide content in the discarded versus consumed tissues of mantid-gutted monarch caterpillars.