Parasites Snoop on Stinkbug Sex

April 19, 2007 — Stink bug mating is so lengthy and lively that egg-colonizing parasites actually eavesdrop on it to their advantage, according to a new study.

The findings represent the first discovery of a parasite, in this case a wasp, eavesdropping on the vibratory sexual signals of another insect. Since some farmers use the parasite to control populations of stink bugs that feed on crops such as soybeans, the discovery might lead to better, natural pest removal methods.

It is possible the wasp evolved the ability to detect stink bug mating, since other creatures — including people — can't.

"Humans cannot hear stink bug vibratory songs without special equipment," lead author Raul Laumann told Discovery News.

Laumann, a scientist at Embrapa Genetic Resources and Biotechnology in Brazil, explained that both male and female brown Neotropical stink bugs vibrate muscles linked to their abdomen and thorax, before and during copulation.

Laumann and his colleagues obtained stink bug nymphs from a Brazilian laboratory colony. The researchers set the stage for mating by rearing the insects on a nutritious diet of sunflower seeds, soybeans, raw peanuts and green beans in a comfortable, humidity-controlled environment.

When the sexes were brought together and mating ensued, the researchers recorded the insects' vibrations. A loudspeaker outfitted with a plastic cone transmitted the vibrations to various parts of a green bean plant. For control purposes, the researchers also transmitted the sounds to polyester printer film. The female egg parasites were then placed on the plant or film.

The researchers found that female parasites oriented their bodies toward vibrations produced by female, but not male, stink bugs. Later, the parasites would preferentially station themselves on leaves where they detected the female stink bug mating movements.

The parasites would lie in wait on the leaves, sometimes for ages.

"In laboratory colonies, mating can occur over many hours," said Laumann, who explained that lengthy copulation is likely a male strategy to ward off competitors in high-density population settings.

Female stink bugs lay eggs right after mating, so the eavesdropping female parasites were then in a prime position to colonize the eggs.

Rex Cocroft, associate professor of biological sciences at the University of Missouri-Columbia, told Discovery News that the study "is a nice piece of work."

"Plant-born vibrational signaling is one of the most widespread forms of communication in the animal kingdom, second only to chemical communication, but is has been seriously under-studied compared to other forms," he said.

Cocroft added, "This paper is exciting because, in a recent review, my colleague Dr. Rafael Rodriguez and I predicted that this form of eavesdropping by predators would be found, so it's nice to see such a prompt confirmation of our prediction!"

Both Cocroft and Laumann think it is likely other mating vibration eavesdroppers exist in nature. These might include spiders, other parasites and certain predators.

The study is published in the current issue of Animal Behavior.