Assessing Transportation Impacts to Alkali Bees (Hymenoptera: Halictidae) and Alfalfa Seed Production in Southeastern Washington State

Abstract

The Washington State Department of Transportation (WSDOT) is proposing safety improvements to U.S. Highway 12 near the town of Touchet, Washington. The improvements include realignment to the north in order to accommodate a wider roadway. The proposed realignment route is within the Touchet-Lowden-Gardena alfalfa seed-growing district, an area critical to alfalfa seed production. The most effective and efficient pollinator for alfalfa is Nomia melanderi Cockerell, a native ground-dwelling bee that is raised in bee beds by area farmers. Relocation of the highway will bisect several bee beds and alfalfa fields. The alfalfa leafcutting bee, Megachile rotundata F., is also an important pollinator in the area. A study was conducted regarding potential impacts to these bees from the highway improvements. One of the objectives of the study was to determine pollinator flight heights over county roads. The “vehicular bee sweeper” was designed to capture insects at specific heights over the roadway and provided data regarding flight height. The majority of N. melanderi flew at heights below 2.1 meters when no other factors were considered, though most M. rotundata flew at or below 0.9 meters. Environmental conditions such as temperature and wind speed had an effect on flight behavior of both pollinators. Due to the low-flying nature of these solitary bees, vehicle strikes can be expected to cause mortality in bisected populations. WSDOT will be able to understand the impacts of the proposed highway to these important alfalfa pollinators and make recommendations to minimize the road’s effects.