2013 Annual Report
1a.Objectives (from AD-416):
We propose to investigate alternative chemistries for control of lygus bugs in alfalfa seed, and predacious beetles in alkali bee beds. Pollination by leafcutting bees, Megachile rotundata, or alkali bees, Nomia melanderi, is essential for seed set in alfalfa seed production. Bee mortality that results from inadvertent exposure to pesticides, disease, parasitism, or direct predation can negatively impact seed yield. In-field pesticide use recommendations are based on the safest timing and bloom conditions for given chemicals, but data on pesticide toxicity to many new chemicals are unknown. In addition, alkali bee nests are subject to predation by ground-dwelling predacious beetles. Azinphos-methyl is the only registered pesticide for control of these predatory beetles, but it only has been granted a 24C registration through 2012, this use will not extend any further due to the fact that the product will no longer be manufactured. Additionally, azinphos-methyl is an extremely toxic insecticide. Thus, alternative controls are needed.
1b.Approach (from AD-416):
We seek to identify compounds that are effective at controlling pests, but that are safe to pollinating bees in alfalfa seed crops. To identify such compounds, we will use three different tests: (1) large-scale, replicated alfalfa seed field tests using 20-acre blocks treated with candidate compounds for lygus control; (2) laboratory bioassays where leafcutting and alkali bees are exposed to treated alfalfa plants; and (3) monitoring of alkali bee beds in Washington state to determine beetle populations. After initial populations are assessed, we will treat the plots with several insecticidal treatments. ARS will provide expertise in bee biology and how to handle the bees for development and mortality studies. The University will conduct the experiments, analyze the data, and write up the reports.
Pollination by leafcutting bees, Megachile rotundata, and alkali bees, Nomia melanderi, is essential for seed set in alfalfa seed production. We surveyed 13 alkali bee beds and focused on bee beds in proximity to the proposed construction sites for the 4-lane upgrade of US Hwy 12 through the Walla Walla Valley of WA. We demonstrate that the previously developed quadrat count method for sampling the underground nests can be used to accurately assess the subterranean larval abundance. We also developed and constructed a “bee sweeper” that was designed to capture insects at 1, 3, 5, 7, 9, 11 and 13 feet above candidate roads. Collectively, 6 selected road miles were sampled in 4 replicated intervals for a total of 52 miles at 40 mph near alkali bee beds in July 2012. This completed the third year of sampling to determine the height at which bees fly across roadways. In 2012, 92% of alkali bees and 98.4% of leafcutting bees were caught at 7 feet or below. Bees flying below 7 feet are obviously going to be impacted by vehicular traffic.
The affect of barriers along side a roadway was evaluated for its effect on bee flight across the roadway for the second year. The roadside barriers did not affect the height at which bees flew across the road, although numerically, the amount of bees caught decreased as one and then two barriers were placed on the sides of the road. In 2012, we expanded the barrier study. We mowed a road through a wheat field adjacent to an alkali bee bed and constructed 6 screen mesh barriers (15 ft x 200 ft) with 2 on one side of the road and 1 on the other side of the road. This was done in two replicates with controls in between. In 2012, results were similar to previous years with other barrier methods, with no significant effect of the barriers on on the number of bees caught in the roadways.
We continued our previous experiments that manipulated the soil temperatures in alkali bee nesting beds using different ground covers. Clear plastic significantly increased soil temperatures in both 2010 and 2011 and increased emergence counts towards the beginning of the alkali bee foraging season. But in 2012, the clear plastic had no significant effect on alkali bee emergence compared to the control.
Due to the deregulation of Round-Up Ready® alfalfa (RRA), RRA fields are placed in isolation of conventional alfalfa fields based on the estimated flight ranges of alfalfa pollinators such as honey bees, alfalfa leafcutting bees, and alkali bees. We will determine the foraging ranges of these pollinators in these fields to make certain the parameters are sufficient to control cross-pollination. This year, alfalfa leafcutting bees were marked with colored UV fluorescent dust at four domiciles within a single alfalfa seed field. Sticky traps were placed at different heights along transects within the field and evaluated in the lab after 24 hours for bee abundance by height and for presence of dye on the bees. Results showed optimal sticky trap height placement to be four feet (1.2 m) above ground. We also discovered limited persistence of the dye on the bees over time, suggesting that using a dust to mark the bees is not an effective marker for this study. Alkali bees were also evaluated. Thirty foraging adult bees (laden with pollen) were collected from their nest sites and frozen in 2012, and the pollen will be tested using AgraStrip®-RUR Strip Tests to determine if the bees visited RRA fields.