Cartoon courtesy
Corky Trinidad
When you pick up the family Christmas tree this season, a major import into Hawaii, don't be surprised if creepy, crawly things fall out before you've finished trimming it.
Each holiday season, our Christmas trees come from the Pacific Northwest inside hundreds of refrigerated sea freight containers--just cozy enough for alien pest species to sleep their way across the ocean and into Hawaii ports.
In a 1988 study, the Hawaii Department of Agriculture found that more than 90 percent of the 448 containers of Christmas trees imported from the Pacific Northwest contained live insects. Since then, HDOA has documented approximately 260 pest species coming into the Islands.
Among the pesky hitchhikers have been snakes, spiders, frogs and bats. The worst, for Hawaii, have been several different species of the yellowjacket (Vespula spp.) queen, a venomous wasp. A colony of yellowjackets will attack anything, or anyone, that disturbs its nest. They also are attracted to food eaten outdoors.
For years the most popular control methods used by the majority of shippers have been a hearty "shaking" of Christmas trees before transport. This procedure is a big help, but not 100% effective.
Now scientists are investigating pre-harvest sprays of pyrethroid insecticides as a means of reducing the risk of rejection at quarantine in various ports throughout the Pacific.
"Yellowjacket queens are probably the most worrisome insect pests found in the trees," said Robert Hollingsworth, research entomologist with the USDA-Agricultural Research Service in Hilo.
According to Hollingsworth, yellowjacket populations already here, such as the western yellowjacket (Vespula pensylvanica) might become more vigorous through interbreeding with newly introduced wasps of the same species. Additional species, such as the German yellowjacket (Vespula germanica) or the common yellowjacket (Vespula vulgaris) might also become established.
HDOA imposed a "zero tolerance" in 1989 for all live yellowjacket and hornet queens in Christmas trees. In response, state Departments of Agriculture in Washington and Oregon, in cooperation with HDOA, initiated an inspection and tree shaking certification program in 1991.
Under the program, exporters were required to shake trees after harvest using either a manual or mechanical shaking method to remove insects.
There has been no published assessment of the method's effectiveness. A new study, co-authored by scientists at the USDA, Washington State University and the HDOA proposes to list interceptions from 1993 to 2006; compare insect infestation levels associated with the two shaking treatments; and, investigate the use of pre-harvest sprays of pyrethroid insecticides as a control supplement.
Unchecked, yellowjackets could expand their range in Hawaii, as each species has its own niche and different ecological requirements. Researchers say the combined control methods that include mechanical shaking, improved inspection protocols and pre-harvest sprays might reduce that risk.
Hollingsworth suggests giving a newly purchased Christmas tree a couple of shakes and rapping the bottom on a hard surface.
"Squash, kill or capture anything that falls out so it won't become established in our environment," Hollingsworth said.
