Possible geologic factors influencing the distribution of the wekiu bug on Mauna Kea, Hawaii : Final report, June 2006

Author:

Porter, Stephen C., R. A. Englund

Title:

Possible geologic factors influencing the distribution of the wekiu bug on Mauna Kea, Hawaii : Final report, June 2006

Year:

2006

Pages:

29 p.

Subject:

Wekiu bug Nysius wekiuicola Geology Mauna Kea

Summary:

The wekiu bug (Nysius wekiuicola Ashlock and Gagne), is a rare species occurring only at the summit of Mauna Kea, Hawaii with only 128 individuals collected in wide-ranging studies by the Hawaii Biological Survey since 2002. Although considerable efforts have been undertaken to learn more about the distribution and ecology of this insect, until now the habitat preferences have not been examined in a geological context. Involving a collaboration between entomologists and geologists, this report marks the first geological assessment of wekiu bug habitat use, with the seemingly consistent pattern of finding these bugs in the uppermost areas of cinder cones throughout the Mauna Kea summit region. Of particular interest is the finding that wekiu bugs are currently only inhabiting areas of the summit that lie within the limit of the glacial ice cap that reached its maximum size about 20,000 years ago, and disappeared by about 16,500 years ago. At the glacial maximum, the ice cap was a broad carapace of ice, about 10 km (6.2 mi) in diameter, averaged about 75 m (245 ft) thick, and covered an area of about 70 km(super 2) (27 mi(super 2)). The highest cinder cones inside the ice limit rose above the glacier, forming nunataks (ice-free areas rising above a surrounding glacier) in the summit region. The distribution of wekiu bugs is related to topography: wekiu bugs have been found predominantly on or near the crater rims of cinder cones that formed nunataks during the last glaciation or that lay at the glacier limit. The increasing altitude of such sites parallels the rise of the glacial-age snowline across the upper slopes of the mountain. The preferred habitat of the bugs is on cinders and spatter near the unmodified crests of cinder cones; the crests of glacially overridden cones apparently lack suitable habitation sites. More significantly, bug habitats are concentrated on these cones in areas where seasonal snow remains longest, i.e., on north- and east-facing slopes and on slopes shaded by local topography. Such snow patches increase in number and area with increasing altitude above the limit of glaciation. Below the glacial limit, seasonal snow quickly disappears and wekiu bugs have not been found. The moist margins of snow patches are places where eolian detritus is concentrated during ablation, thereby providing rich source of food for wekiu bugs.

URL:

http://hbs.bishopmuseum.org/pdf/wekiu-geology2006.pdf

Collection:

Monographs