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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Bee Research Laboratory » Research » Research Project #436762

Research Project: A Pipeline for Streamlined Development and Testing of Novel Controls for the Honey Bee Parasitic Mite Varroa Destructor

Location: Bee Research Laboratory

Project Number: 8042-21000-291-022-A
Project Type: Cooperative Agreement

Start Date: Jun 20, 2019
End Date: Jun 30, 2022

The ultimate goal of this project is to develop and confirm compounds for registration and licensing for beekeeper use. To meet this goal, the project has three research objectives (ROs). Objective 1 (RO 1) will use laboratory trials to screen dozens of candidate compounds and assess their efficacy against Varroa mites and safety for honey bees. Objective 2 (RO 2) will take compounds showing promise from laboratory trials, and run field trials using these compounds in whole honey bee colonies. The third research objective (RO 3) is to elucidate mechanisms conferring Varroa mite resistance to current varroacides and help inform decisions on tested compounds.

The project leverages expertise from six institutions focused on honey bee (HB) health. The Bee Research Laboratory proposes 3 sets of activities corresponding to each of the 3 research objectives: 1- Lab screening trials of candidate compounds to determine acute toxicity of compounds to both Varroa mites (Vd) and host HBs; 2-colony-level field trials assessing effects of candidate compounds identified in RO1 on colony performance and Vd populations, and whether compound residues are found in stored honey; and 3-use of advanced methodology to elucidate the molecular mechanisms granting Vd resistance to active ingredients of current miticides. This work will begin in earnest, and proceed concurrently with laboratory and field trials. Laboratory trials assessing the acute toxicity of screened compounds on Vd mites and HBs will use a widely accepted method employing 20 mL glass vials, and for HBs, 60 mL wide mouth mason jars will have their interior surfaces uniformly coated with a test compound dissolved in a suitable solvent (e.g., acetone), or the solvent alone as a negative control. A suitable positive control will be identified through screening acaricides currently used by beekeepers to both characterize the existing resistance in mite populations (RO3) and to identify an appropriate level of one acaricide demonstrating >95% mortality. The field trials will follow established protocols for colony assessments. For each promising candidate compound identified by RO 1, there will be 4 treatment groups, each comprising 10 colonies: 1) Negative Controls, 2) Low, 3) Medium, and 4) High concentrations. Specific concentrations will be determined for each compound during RO1 dose-titration studies. Application methods will be determined for each tested compound by consensus, and may vary among test compounds, but will most likely consist of cardboard or plastic strips impregnated with compound. Frequency of compound application will also be determined by consensus, and may vary among tested compounds. Every 14 days over the experimental period, (42 days), measurements of colony performance, effect of treatment on Varroa mite population, and samples of stored honey will be taken. The collection of mites to identify the reduced field efficacy of standard varroacides is described in ROs 1 and 2. The varroacide and -resistant mite samples will be divided in two groups and shipped to the investigators’ laboratories for molecular and biochemical analyses as follows: For the molecular analysis of target-site resistance, RNA will be extracted from varroacide and -resistant mites (Group 1 samples) and RT-PCR performed to amplify full cDNA sequences of acaricide target sites. Group 1 samples will be used to estimate the contribution of detoxifying enzymes to the resistance mechanism(s). To further confirm the contribution of the above detoxification enzyme activities to a mechanism(s) of metabolic resistance, the investigators will identify candidate genes that are differentially regulated in the varroacide-resistant mite using global transcriptomic-based gene expression analysis.