The beetles associate the alarm chemicals with a good food source and head for the hive. In Africa, where the small hive beetle is a minor honeybee pest, bees quickly isolate an invading beetle, but domesticated European honeybees are not as diligent in cleaning their hives. The beetles are also aided in their invasion by a yeast that naturally occurs on pollen and produces, as a fermentation product, the alarm chemical that draws the beetles.
"It is possible that bees are being habituated to a low level of alarm hormone," says James H. Tumlinson, the Ralph O. Mumma Professor of Entomology and director of the Penn State Center for Chemical Ecology.
While small hive beetles are common in Africa and pose little threat to African honeybee hives, it appears that domesticated European honeybees have a much harder time containing the beetles in their hives. European honeybees were bred to be docile and easy to work with, while African honeybees are noted for aggression and a propensity to sting. The beetles were first seen infesting U.S. beehives in Florida in the late 1990s.
The researchers tested the response of both the small hive beetles and honeybees to isopentyl acetate (IPA), the major chemical in the bee's alarm pheromones. The first tests showed that when worker bees become alarmed, they produce from 1,500 to 10,000 times more IPA than found in an undisturbed hive. Next the researchers used a gas-chromatagraph-electroantennogram to analyze the chemical sensitively of the insects' antennae. They report in a recent online issue of the Proceedings of the National Academy of Sciences that the beetles could detect the equivalent of 2 nanograms of IPA at the entrance to an undisturbed honeyb