Tuesday, August 26, 2014

Dogbane beetle

What: The end of summer is the time of the insects! I've been watching the dogbane sprout up new shoots, flower, and finally go to seed over the past three months. Because they're a particularly noxious plant (toxic to almost all vertebrates and many vertebrates - they're related to milkweed which is infamous for its implications for monarch caterpillars), they have insects specialized to feeding on them. Similarly, koalas, which exclusively eat the poisonous leaves of eucalyptus, is specialized to eat one and only one thing. The koala's evolutionary trick was to find a way around the defenses of something so toxic that doesn't have any other predators and then exploit that weakness. So too with the dogbane beetle (Chrysochus auratus). Dogbane is a notorious weed in the midwest, largely because it doesn't have any natural pests that control its population.

On the photo at the bottom, I had actually moved it to a milkweed leaf right next to the dogbane where I found it. There were a number of milkweed aphids on the underside. Once the beetle had crawled to the underside of the leaf it kept stomping its feet and then would fly a few inches to a new spot. It seemed really perturbed by the significantly smaller beetles. After about 30 seconds of "torment" it flew to another leaf.

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