Location: Bee Research Laboratory
Project Number: 8042-21000-291-040-I
Project Type: Interagency Reimbursable Agreement
Start Date: Feb 1, 2021
End Date: Sep 30, 2021
The goal of the research is an integrated effort against Varroa mites using our expertise in honey bees, mite biology, virology, and chemical ecology. Five distinct objectives are: 1) Refine understanding of Varroa mite ecology, including the roles of chemical cues that direct mite movements among colonies; 2) Identify the roles of seasonality and mite/host physiology underlying variable susceptibility of Varroa mite to toxicants; 3-4) Provide data and analyses that identify the contribution of host-derived proteins to Varroa mite reproduction, and their movements within Varroa mites and/or their eggs, and produce an atlas of histological preparations of reproductive female mites; and 5) Understand mechanisms of Varroa-mediated transmission of honey bee viruses.
For Objective 1, the focus will be on understanding whether and how colony mite loads, which may be correlated to levels of in-hive chemical cues, affect movements of mites among colonies. First, we will leverage the many colonies used as ‘mite farms’ on USDA-ARS grounds and monitor/measure their mite levels. Then, repeating the study from FY2019, we will sample in-coming and out-going honey bees and determine the number of mites they carry. Finally, we will artificially increase/decrease colony mite load and re-evaluate mite movements among colonies. A hypothesis for this work based on results from FY2019 states there will be a net emigration of mites from colonies with lower manipulated mite loads and net immigration of mites to colonies having manipulated higher mite loads. For Objective 2, we will use established toxicological methods to determine the Varroa mite LC50 for key varroacides, including amitraz, fluvalinate, and coumaphos at several points over the spring/summer and fall/winter seasons. At these same time points, we will determine the antioxidant capacity, activities of several antioxidant/detoxification enzymes, and the expression of the genes producing these enzymes for both the mites and their honey bee hosts. We will also quantify the levels of host-derived proteins (vitellogenin, heat shock proteins, etc.) in both hosts and mites, and use these data as explanatory variables in analyses of the mites’ response to chemical exposure. For Objective 3-4, we will use in-house protocols and resources to track movements of host-derived resources (e.g., proteins, lipids) ingested by mites through their bodies and into developing eggs. Tissue preparations of mites treated with tissue-specific stains and/or with host specific antibodies will be collected along a time series (from ingestion to egg laying, an approximately 30-hour time span) and analyzed using microscopy, will help decipher the major locations (sinks) for specific tissues within the parasites. The lyrate is hypothesized to be a sink of many of the host-derived proteins sequestered by Varroa mites. For Objective 5, we will use in-house generated genetically tagged, cDNA-derived honey bee viruses (e.g., deformed wing and varroa destructor 1- viruses (DWV-A and VDV1)) to unravel key aspects of Varroa-mediated vectoring and transmission of DWV-like viruses to honey bees.