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.
3. Progress Report:
Pollination by leafcutting bees, Megachile rotundata, and alkali bees, Nomia melanderi, is essential for seed set in alfalfa seed production. Field experiments were continued this year to evaluate the impact of various environmental factors on bee health. (1) Population Monitoring in Alkali Bee Nesting Beds: A hydraulic soil core device was developed and constructed for sampling bees in underground nests. Thirteen bee beds were surveyed in proximity to a proposed road construction site for a 4-lane upgrade of US Hwy 12 through the Walla Walla Valley, an area where alfalfa pollination depends on alkali bees. Twenty four 0.5-square meter quadrant counts were taken per sampled bee bed using a method developed by ARS (Logan, UT). Eight cores were sampled per quadrant in October 2011. The larva present in these samples was quantified that winter. A regression analysis will be conducted to determine how effectively the surface counts predicted by the ARS method estimates subterranean larval abundance. (2) Alkali Bee Flight Monitoring: 54 pane-traps were set up at 4 different heights (0, 3, 6, 9 ft) around the perimeters of 3 bee beds. Significantly more bees were found at 0 and 3 feet than at heights of 6 or 9 feet. A “vehicular bee sweeper” was developed to capture bees flying at 1, 3, 5, 7, 9, 11 and 13 feet above candidate roads, and then 6 road-miles near alkali bee beds were sampled for bees flying across the road. The road was sampled in 4 replicated intervals for a total of 24 miles at 40 mph. This provided a second year of data on bee flight height. The majority of bees flew below 7 feet, a height where they are obviously going to be impacted by vehicular traffic. (3) Barrier Study: We constructed a screen-mesh barrier at a height of 15 ft and span of 150 ft on both sides of a road adjacent to an alkali bee bed to see if this could detract the bees from flying across the roadway at vehicular heights. The vehicular bee sweeper was driven down this stretch of road in replicated intervals when there were either no barriers, one barrier on the side of the road with the bee bed, or when barriers were present on both sides of the road. No statistical significance was found between heights bees were found or the amount of barriers present, though numerically, the amount of bees caught decreased when one and then two barriers were placed on the sides of the road. (4) Alkali Brood Emergence Study: Alkali bee beds were marked off into square meter plots and then soil surface treatments were applied, including a) white chalk dust, b) black plastic, c) clear plastic, d) red plastic, e) brown plastic, f) blue plastic, g) white on black plastic, and h) untreated control. We were attempting to manipulate soil temperatures and regulate alkali bee emergence. The clear plastic significantly increased soil temperatures at one of the sites and increased early emergence counts at both sites. White chalk dust and white on black plastic both significantly decreased soil temperatures at both sites and delayed emergence in the first few weeks of brood emergence.