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Growing wasp population pushes out local species


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POSTED: Sunday, July 26, 2009

Invasive wasps on Hawaii island and Maui have expanded their diet to the point where they are disrupting the populations of native insects, spiders and birds, a new study has found.

Their nests have grown thousands of times larger, too, with the sheer numbers of predators changing the ecology of endangered ohia woodlands and subalpine shrublands, says the lead researcher, Erin Wilson of the University of California at San Diego.

“;They're consuming anything from geckos to shearwaters to tree lice to more juicy items that you would expect them to eat, like caterpillars,”; Wilson said last week in an announcement of the findings. “;They're just like little vacuum cleaners.”;

In the fall of 2006 and 2007, Wilson traveled to Hawaii Volcanoes National Park and Haleakala National Park to study the wasps, also known as western yellowjackets, or Vespula pensylvanica.

In research reported in the Proceedings of the National Academy of Sciences, she collected DNA from bits of prey from wasps returning to their nests. The DNA was traced back to a wide array of animals, even reptiles and birds.

The wasps are also feeding on nectar in competition with native species.

“;It's not just what they're killing,”; Wilson said. “;They're also collecting great amounts of nectar, drawing down the resources for anything else that might want to feed on it, whether it's native insects or birds like the Hawaiian honeycreepers.”;

On the mainland, the wasps usually build a nest in the spring that becomes dormant in the winter. But Hawaii's mild climate has allowed many to stay active year-round.

Up to 20 percent of colonies persist for years, growing to enormous sizes, said Wilson. One colony on Maui had as many as 600,000 individuals, she estimated, compared with the usual size of a few thousand.

“;Rather than having a nest the size of a football, you'll have a nest the size of a '57 Buick,”; Wilson said. “;Our largest colony had four nest entrances that were just like fire hoses of wasps coming in and out.”;

Although wasps will scavenge food from carcasses, more than two-thirds of the confiscated food bits were from freshly killed prey, including spiders, flies, crickets, bark lice and rare Hawaiian bees, they found.

Wilson and her colleagues found that nearby populations of caterpillars increased by 86 percent and spiders by 36 percent when rangers removed wasp nests.

The study was funded by the National Science Foundation and the Environmental Protection Agency.