Skip to main content
ARS Home » Pacific West Area » Logan, Utah » Pollinating Insect-Biology, Management, Systematics Research » Research » Research Project #434566

Research Project: Enhancing Pollination by Attracting and Retaining Leaf Cutting Bees, Megachile rotundata, in Alfalfa Seed Production Fields

Location: Pollinating Insect-Biology, Management, Systematics Research

Project Number: 2080-21000-019-16-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Jul 1, 2018
End Date: Jun 15, 2021

The USA is the largest alfalfa producer in the world. Alfalfa contributes more than $10 billion per year to the nation’s economy, primarily through its use as animal feed. Seed production occurs primarily in California and the Pacific Northwest and bees are required for pollination. Honey bee is the major managed pollinator used in CA, whereas alfalfa leafcutting bee (ALCB) dominates in the Pacific Northwest and is becoming more important in CA. A smaller acreage is pollinated by the alkali bee, mostly in the northwestern USA. Since its arrival in the USA in the 1940s, the ALCB, Megachile rotundata, has become “the world’s most intensively managed solitary bee” and its role in alfalfa seed production has been increasing. An important problem with the commercial use of ALCBs in alfalfa seed production is the significant loss of bees when they are released into a field. Pollinators respond to the visual display and odor bouquet of flowers that serve as the source of nectar/pollen; in addition, solitary bees also use odors associated with their nests to find their nests and continue provisioning and egg laying. This process underlies their activities to gather pollen and pollinate the crops. Complex blend of volatile organic chemicals define the attraction to floral bouquets (VOCs) that are detected by the antennae, thus generating unique olfactory code based on the chemical properties of VOCs. Similar cues may also be used in nest finding. Thus a better understanding of the olfactory signals the nesting blocks and their detection by the ALCB will provide insights that can be exploited to enhance the attraction of ALCB to alfalfa crops and retaining them for extended periods. In this study, we will identify the attractive VOCs from ALCB fecal rings and leaf cuttings that have been previously shown to attract ALCBs with the goal of creating attractive blends that can be used as baits to help maintain ALCBs in a field and decrease the quantity of ALCBs needed for alfalfa seed production. Objectives: 1. To determine the exact relative amounts of the biologically active constituents in ALCB fecal rings or leaf cuttings to reconstitute a synthetic blend and formulate it as field deployable baits. 2. To test the impact of the odor (VOC) bait in maintaining ALCBs to their respective domiciles upon release in alfalfa seed-production fields.

Identification of the biologically active volatile organic compounds in ALCB fecal rings and leaf pieces will be made by extraction, separation by gas chromatography (GC) and linked to electrophysiological analysis. The compounds eliciting a positive antenna signal will then be subjected to behavioral evaluations. Optimal ratios of the compounds will be determined and then the optimal attractive blends will be added to slow release polymers. Under semi-field conditions, the blends will be tested for their impact in attracting/retaining ALCB. If successful in the semi-field conditions, the baits will be tested in alfalfa seed production fields. The baits will be deployed using an experimental design to evaluate the placements and the differential attractiveness of the ALCB to domiciles with and without the baits. The number of cells formed per bee and per domicile will be compared.