Assessing transportation impacts to alkali bees (hymenoptera: halictidae) and alfalfa seed production in the Walla Walla Valley.

摘要

Alkali bees, Nomia melanderi, are native, solitary, soil--nesting bees commercially managed in southeastern Washington State. They nest in dense aggregations and are important pollinators of alfalfa produced for seed. The Washington State Department of Transportation (WSDOT) proposed safety improvements to US Highway 12 through the Touchet-- Lowden--Gardena alfalfa seed growing district, an area critical to alfalfa seed production. This includes northern realignment to accommodate a wider roadway and avoid impacting any towns. Relocation of the highway will bisect several N. melanderi nesting aggregations and alfalfa fields. The study has three objectives: 1) survey the population abundance of N. melanderi across the region by comparing two sampling techniques; 2) determine bee flight heights across roads; and 3) determine N. melanderi foraging range using transgenic pollen.;Regression was significant between the two population sampling methods. Mean emergence hole counts, mean prepupal counts, and the surface area of the nesting aggregations, were used to estimate the abundance of N. melanderi in each bee bed. We constructed a "vehicular bee sweeper" designed to capture insects at specific heights over the roadway. The majority of N. melanderi flew below 2.1 m when no other factors were considered, but environmental conditions like temperature and wind speed affected number and flight height of N. melanderi. To determine N. melanderi foraging distance, adults were collected from their nest sites, and pollen on their hind tibia was tested for the presence or absence of Roundup--RTMReady alfalfa (RRA). The minimum foraging distance was 0.04 km and the maximum was 4.62 km. These distances suggest that N. melanderi will cross the highway for floral resources, increasing potential mortality.;Studying N. melanderi population abundance and flight characteristics allows us to understand the potential impacts of the proposed highway on bee populations and on alfalfa seed producers. The non--destructive quadrat method of sampling N. melanderi populations is robust compared to the destructive, labor-intensive, soil core method. Due to the low-flying nature and foraging distance of N. melanderi, vehicle strikes can be expected to cause mortality in bisected populations. Ultimately, recommendations will be made to highway designers to minimize and mitigate these effects.