Volcano Watch — 'Tis the season to say goodbye to yellowjacket wasps

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Last week's heavy rains on the Big Island brought an end to one of the worst seasons for yellowjacket wasps around Mauna Loa in more than a decade.

Last week's heavy rains on the Big Island brought an end to one of the worst seasons for yellowjacket wasps around Mauna Loa in more than a decade.

The western yellowjacket wasp (Vespula pennsylvanica) has plagued montane areas of the island since 1978. An alien species introduced from the Pacific Northwest, the yellowjacket undergoes seasonal population irruptions during the summer and fall months and is a particular nuisance to campers, picnickers and hikers in upslope areas in the autumn.

Yellowjackets here are commonly called "bees" because of their similar appearance to honey bees, their habit of building large colonial nests, and the painful sting they inflict when either they or their nest are disturbed. However, there are important differences that separate wasps from bees and make yellowjackets an important problem for Hawai`i. In particular, while bees perform vital services as pollinators of many native plants and agricultural crops, wasps are generalized predators and prey on other insects indiscriminately, including many beneficial species.

Research conducted by Department of Interior biologists in Haleakalā and Hawai`i Volcanoes National Parks has demonstrated that the western yellowjacket wasp preys on many endemic insect species, thereby potentially reducing prey for insectivorous Hawaiian forest birds and interfering with pollination of rare native plants.

The western yellowjacket was accidentally introduced to the island of Kaua`i in 1919 and subsequently reported on O`ahu in the 1930s. After that there is a hiatus of more than four decades before the wasp spread throughout the rest of the major Hawaiian Islands in the late 1970s. This last rapid expansion of its range coincides with the increased use of refrigerated containers for shipping Christmas trees to Hawai`i from Oregon and Washington. Inspections of Christmas tree shipments by the Hawai`i State Department of Agriculture have resulted in the interception of numerous yellowjacket wasps.

To understand the relationship between Christmas trees and the wasps, it is necessary to know more about the biology of yellowjacket. Like honey bees and many species of ants in Hawai`i, yellowjacket wasps are considered social insects because of a life cycle that includes a queen who establishes a colony of non-reproductive workers. In the case of western yellowjackets, these colonial nests are built in the ground, frequently under a rotten log. The nests are generally seasonal, starting in the late spring and growing throughout the summer.

As fall progresses, the colony switches from producing workers to the production of new reproductive queens. These queens ultimately leave the colony, mate with drones (male wasps), and remain inactive until the following spring. Heavy winter rains and cold temperatures combine to destroy most of the previous season's colonies.

Judging from the large number of yellowjacket queens that have been intercepted in Christmas tree shipments, it appears that these small trees provide attractive shelter for the queens once they mate and leave their colony. As the trees are wrapped and stacked for shipment, the wasps remain with the trees until they are unloaded in Hawai`i. Yellowjacket wasps are only one of many groups of invertebrates, newts, salamanders and frogs that make their way to Hawai`i via Christmas tree shipments.

In the 1980s, Hawai`i worked with Oregon and Washington to develop sanitation procedures, including the shaking of Christmas trees before shipment, and this has virtually eliminated yellowjackets in Christmas tree shipments to Hawai`i. Meanwhile, biologists at the U.S. Geological Survey and the National Park Service have developed monitoring programs for the wasps and are experimenting with methods of reducing their numbers during the peak months of summer and fall.

The deluge of rain last week is an important natural check that has eliminated most yellowjackets from upland picnic areas and trails until next summer.

Volcano Activity Update

Eruptive activity of Kīlauea Volcano continued unabated during the past week. Lava is erupting from Pu`u `O`o and flowing through a tube to the southeast in the direction of the ocean to a complex of perched lava ponds above Pulama pali. Two flows originate from the perched pond complex. As of December 9, the longer-lived, western flow was down below Paliuli at an elevation of 15-m (50-ft) and a distance of 0.85 km (0.5 mi) from the coastline. The flow is crusted and tubed over from the top of Pulama pali to Paliuli. Lava is ponding at the base of Paliuli and must fill a swale before it can move seaward. The second flow is located to the east of the older flow and has advanced down to the base of Pulama pali where lava is ponding at an elevation of 75-m (250-ft). A lobe from the eastern flow has traveled to within 0.9 km (0.54 mi) of the Royal Gardens subdivision but is now blocked by an earlier flow from progressing farther.

There were no earthquakes reported felt during the week ending on December 9.