Their understanding of the system has implications for controlling coffee pests, such as green coffee scale (Coccus viridis), a flat, featureless insect that lives on coffee bushes. On some bushes, Azteca ants protect the scale insects from predators and parasites and in return collect honeydew, a sweet, sticky liquid the scale secretes.
One of the green coffee scale's mortal enemies is a beetle whose adult and larval forms both feed on it. "When an adult beetle comes to eat the scale insects, the ants vigorously defend the scales against attack," Vandermeer said. "So within these clusters, the beetle can't eat its prey." The adult beetle, that is. The larval beetles evade the ants with waxy secretions on their backs that gum up the ants' mouthparts.
Not only are beetle larvae able to polish off plenty of green coffee scale, they also get an inadvertent assist from the ants. In the course of shooing off parasitic wasps that attack scale, the ants also scare away bugs that parasitize beetle larvae.
"So we have a situation where the beetle is the main predator of the scale insects, which are pests on the coffee, and that beetle would go extinct if not for the patchy distribution of ants, because the larvae can only survive with the ants, and the adults can only survive without them," Vandermeer said. "The farmers see the ants protecting the scale insects and want to eliminate them. But what we've discovered is that the ant, by forming these clusters, is a key component to maintaining the main scale insect predator in the system."
|Contact: Nancy Ross-Flanigan|
University of Michigan