by PATTI J. ELZEN, Ph.D
USDA-ARS
Weslaco, TX


We in the research community receive frequent requests for information on alternative means of controlling varroa in managed hives. This is particularly relevant in light of failures of the currently registered compounds to control varroa that have developed resistance to these compounds. In this column I'd like to cover one approach that I've gotten several queries about - use of food grade mineral oil to reduce varroa in hives.

Late last year I received a call from Bob Brachmann in New York asking if I could give him guidance on how to set up a trial to test mineral oil. If mites are present, an efficacy trial is actually quite easy to do. I advised Bob he needed to compare the food grade mineral oil treatment with a standard industry treatment (he chose coumaphos) and a reference untreated "control". These three groupings then needed to be replicated, so that variation in hive responses could be measured and used for analysis of data.

Bob chose to run three hives per group - three food grade mineral oil hives, three coumaphos hives, and three untreated hives. The food grade mineral oil was applied using an atomizer, the coumaphos was applied as a strip in the brood nest and the control was untreated. The final factor to consider was how to measure the mite numbers, PRIOR TO and AFTER treatment. It is very important to have a pre-treatment assessment - without having a number of how many mites there were to start, how would one know if the treatment actually reduced mite numbers? Bob chose to use an alcohol wash of a known number of bees from each hive. This is a good method - more accurate than ether rolls and less cumbersome than sticky boards. The trial was set up on March 22, 2003 in Virginia, and resampled for post-treatment mite numbers on April 6, 2003. In working out the plan, Bob was very clear he would be using Russian bees in the trial, in an effort to conduct not just an efficacy trial, but also the integration of two control techniques - host resistance and non-synthetic pesticides. Combining the methods would not be expected to confound the results - all nine colonies were Russian, so all colonies were comparable. Only treatment was varied.

What Bob found was the coumaphos gave 100% reduction of mites during the treatment interval and the untreated hives remained about the same overall. The food grade mineral oil treatment gave 69.4% reduction of mites at the final assessment.

As I have stated elsewhere, the idea of combining multiple tactics for varroa control is one of the best long-term strategies for pesticide use reduction, minimization of resistance, and environmental safety (to bees and humans). The value of 69.4% reduction is quite acceptable when used in coordination with another control tactic; here as Bob chose, of a partially-resistant bee line. The real proof of the pudding comes over long-term success of the multiple strategies - can the two together, while not giving 100% control on their own, add up to effective control and colony survival over the long haul? This is the next step in pursuing an approach such as this in generating data on food grade mineral oil - a step I will take in an upcoming trial building on the trial Bob conducted. How difficult it would be to pursue food grade mineral oil registration for in-hive use is another matter which deserves consideration.

The adoption of food grade mineral oil in controlling varroa could be another tactic to use in rotation for a successful management program. Currently the Weslaco lab is generating data to submit to the EPA for registration of two natural compounds, both of which could also serve as additional rotational materials. Other compounds are being investigated experimentally at the present time, but it may be quite some time before they would be considered for approved registration.

In the final analysis, what the industry needs is as many control tactics as possible for integration into a comprehensive management plan. The more compounds we have to use in a rotational plan, the better.