It all started in the 1970s, when the U.S. Department of Agriculture picked a number of non-native ladybug species and decided to mass-rear them and turn them loose in the United States," explains Peter Kareiva, professor of zoology. "They were brought in to control aphids, and they adapted extremely well. Now they are extraordinarily abundant."

How abundant? Kareiva, who has studied native ladybug species (there are 450 species in the U.S. and 5,000 worldwide) at Mt. St. Helens for ten years, says that while he used to find a healthy mix of native species there, he now sees almost all "exotics," or non-native ladybugs.

Several years ago, recognizing that a problem might be brewing, the U.S. Department of Agriculture (USDA) funded Kareiva to quantify the extent of the invasion. Kareiva and colleagues sampled numerous habitats—24 in Washington state and 20 in Virginia—and recorded the number and species of ladybugs they observed. "The sites included some fairly remote spots in the Cascades, to see if the exotic ladybugs had reached remote places," Kareiva says. "As it turns out, they had. It was hard to find a place where they were not present."

Kareiva’s findings were sobering. More than 80 percent of the ladybugs encountered were one of two exotic species introduced in the ‘70s: the seven-spotted ladybug and the many-spotted ladybug. The native species were being usurped.

Is this cause for concern? In terms of biodiversity, the answer is an easy "yes," since the exotic species’ success could lead to the extinction of native species. In terms of pest control, the answer is less clear.

"If we can learn why these two species are so successful, that may provide some answers," says Kareiva, who has received additional funding from USDA to explore this question.

Kareiva explains that all ladybugs engage in cannibalism—that is, they eat their young or the young of other species. The question is whether the two exotics are eating the young of other ladybugs at such a rate that they are reducing the total number of ladybugs available to eat aphids.

"We don’t have ‘before’ and ‘after’ data to know whether the overall population is increasing or decreasing," says Kareiva. "That’s a problem with a lot of biological research. There’s the sense that things are changing, but that data aren’t available until it’s almost too late."

Kareiva and his colleagues are studying the two exotic and two native species in a controlled study to compare their behavior. "We put them in small cages with plants and aphids and check them every day for five days to see what happens," he says. A similar ladybug drama will be played out on a larger scale in a contained area of a field, with Kareiva checking those subjects weekly.

The results of this study will have significance beyond the ladybug question. The research feeds into larger issues about pest control, with political implications. "A lot of pesticides are coming up for re-regulation," says Kareiva. "Decisions must be made about whether they will be re-licensed. Biological pest control will be getting a lot of attention in this debate, so it is important that we gain a much better understanding of what makes biological control work or not work. My hope is that this study will add to that understanding."