Hawaii gains respite from ‘Christmas Tree’ wasps

Heavy rains have brought Hawaiians relief from a particularly bad outbreak of an alien wasp species that was originally transported from mainland US in shipments of Christmas trees.

Numbers of the western yellowjacket wasp increase during the summer and autumn as the queen produces non-reproductive worker wasps, causing a nuisance to campers, picnickers and walkers in highland areas of the Hawaiian islands.

Research has shown that the wasps, which resemble bees, prey on many indigenous insect species, reducing the amount of food available to insectivorous Hawaiian forest birds and reducing the pollination of native plants.

The yellowjacket was first introduced to the island of Kaua’i in 1919 and then spread to O’ahu in the ’30s. There were no further reports of the alien species until the late 1970s, when they appeared on the rest of the Hawaiian islands.

Upon investigation, it was discovered that the wasps were being transported in refrigerated Christmas tree containers from Oregon and Washington.

Queen wasps leave their nests in autumn, mate with male wasps and then lie dormant until the spring. Rains and falling temperatures destroy most of the previous season’s colonies. Meanwhile, Christmas trees can provide perfect shelter for the queens after mating. Such trees are often wrapped for shipment to Hawaii.

Simple measures, such as the shaking of Christmas trees prior to shipment, were introduced in the 80s, alleviating the problem. Although the wasps disappear in the winter, their numbers during the summer and autumn continue to rise. The US Geological Society and the National Park Service are researching how to tackle the problem during the peak season.

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