Technical Report #185. Magnacca, K.N. and C.B.K. King. 2013. Assessing the presence and distribution of 23 Hawaiian yellow-faced bee species on lands adjacent to military installations on O'ahu and Hawai'i Island. 39 pp.

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ABSTRACT:
The endemic Hylaeus bees are critical pollinators in native ecosystems in Hawai'i. Seven
species are proposed for listing as endangered, and many more are rare and potentially
endangered. We surveyed 40 localities on O'ahu, 56 on Hawai'i, and approximately 70 km of the coastline of Hawai'i for 23 species of native Hylaeus, including four added during the course of the project. All of the native Hylaeus were much rarer than they were during previous surveys in 1999 through 2002, including many previously considered common. The only target species found in significant numbers was H. anthracinus, which is restricted to narrow strips of seashore vegetation on both islands but can occur in high density where present. However, the largest O'ahu population, at Ka'ena Point, appears to have completely disappeared since it was last observed in 2002. Significant populations exist on Hawai'i, but only two sites are currently known on O'ahu. Six of the other species on O'ahu were not seen at all, and the remaining six (H. anomalus, H. laetus, H. makaha, H. mamo, H. mana, and H. mimicus) were collected once or twice and/or with a total of 1 to 5 individuals each. On Hawai'i, only H. flavipes, H. kona, H. laetus, H. ombrias, and H. rugulosus were collected, mainly from in or around Pōhakuloa Training Area during a brief period of July and August. Most non-target species have been found at least once, but nearly all in low numbers; some of the less common ones, including H. setosifrons on Hawai'i, were extremely rare or absent. The past several years have been extremely dry on the leeward sides of the islands, where most of the rare species occur, and drought may be a factor in the low numbers of bees. Serious damage and mortality among Myoporum sandwicense, an important floral resource, as a result of thrips infestation may also be important in reducing numbers and diversity of bees in montane areas of Hawai'i. These results indicate that management of Hylaeus for recovery will be difficult, particularly at montane sites, but that the conservation need is also increasingly urgent as invasive species and climate change are having a greater and more rapid impact than anticipated. In coastal sites, the alien tree Heliotropium foertherianum (=Tournefortia argentea, tree heliotrope) is a critical floral resource for Hylaeus and should be managed with careful regard for impacts on bee populations.