Hawaii fights invasive yellowjackets

WASHINGTON, Dec. 16 (UPI) -- Hawaiians may soon be able to worry less about finding yellow-jackets living in their Christmas trees shipped from the mainland United States, scientists say.

Fir trees from the Pacific Northwest are harvested and shipped to Hawaii for use as Christmas trees, and although yellow-jackets usually nest in the ground, mated queens who haven't yet built their nests sometimes make fir trees their home during winter, a U.S. Department of Agriculture release says.

The western yellow-jacket is considered an invasive insect in Hawaii, competing with native birds for insect prey and greatly reducing native insect populations, the USDA said.

In an effort to keep yellow-jackets from reaching the islands, Hawaii officials have required a percentage of trees to be either manually or mechanically shaken to dislodge insect pests.

Researchers at the USDA's Agricultural Research Service found that both methods failed to remove all yellow-jacket queens from the trees, although mechanical shaking was significantly more effective than manual shaking.

USDA scientists tested pre-harvest insecticide sprays as a supplement to the shaking treatment and found mist applications of an insecticide in the pyrethroid chemical class were 100 percent effective in killing yellow-jacket queens, and remained effective even after heavy rainfall.

While tests on pesticides continue, Hawaii officials require all fir trees destined for the islands to be shaken by one method or the other, the USDA reports.