Location: Bee Research Laboratory
Project Number: 8042-21000-291-077-I
Project Type: Interagency Reimbursable Agreement
Start Date: Mar 1, 2024
End Date: Sep 30, 2025
Objective:
The objective of this agreement is to fund projects that may inform U.S. beekeepers of management strategies for use against Varroa mites. Varroa causes both direct and indirect damage to their honey bee hosts, through feeding and vectoring of pathogenic honey bee viruses, respectively. Varroa infests both adult and pupal honey bees during their dispersal/phoretic and reproductive life stages, respectively. Varroa have gained resistance to several key conventional pesticides containing Fluvalinate, Coumaphos, and most recently, Amitraz. Biopesticides, such as the organic acids formic and oxalic, are also used but have restrictions in their effectiveness and timing of use. Fortunately, Varroa is not likely to gain resistance to the effects of these biopesticides, and formic acid treatment can reach the mites under wax-capped pupal cells, and advantage other treatments lack. Additional ‘cultural’, non-chemical methods, such as mite trapping in drone brood, which are then discarded, are also used to control Varroa, but are not typically useful without the concomitant use of a chemical control. Thus, for these reasons, other control methods are needed by beekeepers to reduce the harmful impacts of these mites. The projects planned under this agreement will (1) test a novel compound for its use against Varroa, and (2) investigate the utility of a non-chemical method for reducing the mite population growth. For (1) we will test whether mesoxalic acid, which is dicarboxylic acid derivative, can be used as a varroicide. This compound is of interest because it contains both an oxalic and formic acid moiety, which may break apart into separate constituents under thermal conditions. It is not known, however, whether this is the case. To test this, ARS will need to subject an amount of the compound to thermal conditions and collect the resulting materials for analysis using GC-MS/MS. For project (2) we will investigate the utility of a non-chemical method of Varroa control that involves opening capped brood cells to disrupt the reproduction of the mites. This idea follows the knowledge that some honey bees are hygienic against Varroa infestations. Bees from colonies of this hygienic stock open the caps of pupal cells exposing the brood, but do not remove the pupae from the cells. It has been determined that this behavior disrupts/delays the reproduction of Varroa, resulting in far fewer mites reaching maturity before their host emerges from the cell as an adult honey bee. This behavior keeps mite levels very low. We aim to artificially replicate this in non-hygienic honey bee colonies (most colonies do not exhibit this behavior) and will monitor the population growth trajectory of mites from colonies receiving or not receiving this treatment.
Approach:
For project (1), methods will include heating 0.5 g of mesoxalic acid (BOC Sciences, USA) using an ProVap temperature-controlled heating unit (Oxavap, USA), a device employed by beekeepers to apply sublimated oxalic acid to bee colonies and collecting generated vapors using an absorptive filter (volatilecollectiontrap.com). Any remaining material post-heating will also be collected and analyzed to determine chemical constituents. ARS will run the experiment 2-3 times, adjusting the temperature from ~210 to 235 C (overlapping with vaporization point of related compounds). Vapor components collected on absorptive filter and any remains in heating unit will be dissolved in hexane, concentrated under Nitrogen gas and analyzed using GC-MS/MS. Samples for analysis will be sent to the Biochemistry Department at the University of Maryland, College Park.
For project (2), methods will include establishing ~40 honey bee ‘package’ colonies in April 2024 and allowing them to become established. Once established, the Varroa populations of the colonies will be monitored using sticky traps installed under screened bottom boards of the bee hive boxes. Colonies will be inspected for whether they exhibit pupae uncapping behavior, and if so, these colonies will be omitted from the experiment. Remaining healthy colonies will be split into either treated or untreated colonies. To apply treatment, frames containing capped pupae (drone and worker) will be removed and wax-capped cells will be gently perforated using a tool used to uncap wax-capped honey cells (Mann Lake, USA). Frames will be placed back in colonies once the perforations have been completed. Colonies will be monitored for whether (and how quickly) worker bees recap the brood cells, and survival of the pupae. The process will be repeated every 10-14 days to assure that newly capped brood cells are also perforated. This experiment is not determining the mechanism of how Varroa reproduction is disrupted from perforating pupal cell caps but rather whether doing so has the effect of reducing mite population growth. For this, Varroa populations will be monitored continuously (July-October) using sticky boards and periodic (every 3-4 weeks) alcohol washes of approximately 250 adult honey bees.
