Reducing Pesticide Use in Honey Bee Colonies through Sound Sampling and Treatment Procedures
Preliminary analysis showed that a single sample of 200 bees adult bees per colony provided the best precision level (0.25) to determine the mite (Varroa destructor) load and to make management decisions for an apiary. These conclusions will be verified through further sampling. Guidelines will be developed to help beekeepers make educated treatment decisions based on the sampling plan. Our line of bees bred for both Hygienic Behavior and Suppression of Mite Reproduction had significantly lower mite levels compared to an unselected line of bees demonstrating that this line can reduce mite loads and thus the frequency of pesticide application.
The continuing, long-term goal of this research is to reduce the amount of pesticide use in honey bee colonies for the control of the parasitic mite, Varroa destructor. Most commercial beekeepers do not sample their colonies to determine if the mite levels have reached an economic threshold, and hence to determine whether to treat or not, which has led to the overuse of pesticides and the subsequent development of resistance by the mites to the chemicals. To foster more sustainable beekeeping practices, and in response to beekeeper demand, we propose the following objectives:
Objective 1. Develop a simple and standardized sampling plan for commercial beekeepers to help them determine the economic treatment level for Varroa destructor mites (short-term outcome).
Objective 2. Compare mite levels between our line of bees bred for both Hygienic Behavior (HYG) and Suppression of Mite Reproduction (SMR) with an unselected, commercial line of bees (short-term outcome), to demonstrate that the use of resistant bees can reduce mite loads and thus, the frequency of pesticide application (intermediate-term outcome).
Objective 3. Develop published guidelines for migratory beekeepers on making educated treatment decisions for the mite based on the sampling plan (intermediate- to long-term outcome).
Objective 1: It is relatively common for growers to sample insect pest populations in a field crop to help them make an educated treatment decision. Our goal is to encourage beekeepers to sample their bee colonies for mite pest populations in a standardized way to help them make wise treatment decisions. Such a sampling plan for a mite pest in an insect colony has never been attempted. Based on sampling statistics developed by Dr. Bill Hutchison, we estimate that we need to sample bees from 30 apiaries (32-40 colonies/apiary) to obtain sufficient data to develop the sampling plan. In June and September 2005, we sampled colonies of bees for mite infestation on adult bees in 12 apiaries in MN and ND.
In 2006, we sampled 10 apiaries, bringing our total to 20 apiaries. We plan to complete the last 8 in spring of 2007. Katie Lee, graduate student funded on this project, is currently processing the samples in the lab. A nested analysis of variance based on samples from the initial 12 apiaries revealed that the main source of variation among mite data occurred at the colony level explaining approximately 25% of the variation among samples. The mite dispersal pattern was determined at the colony level using Taylor’s power law and indicated an aggregated distribution (b-value > 1) for all sample units tested. Thus far it appears a single sample of adult bees can be taken from a colony to determine the mite load. The mite load can then be determined for multiple colonies in an apiary to make management decisions for an apiary. Also, a sample unit size of 200 bees provided the best precision level with the smallest sample size unit providing an average precision level of 0.25 (acceptable for pest management) over an average sample size of 11 colonies in an apiary. These conclusions will be verified through further sampling and data analysis in 2007.
Objective 2. We compared colonies selectively bred for both hygienic behavior and Suppression of Mite Reproduction (HYG/SMR) with colonies bred solely for hygienic behavior (HYG) and unselected control colonies. Colonies were evaluated for strength, brood viability, removal of freeze-killed brood, honey production, mite loads on adult bees and within worker brood, and mite reproductive success on worker brood for two years in two locations (MN and ND).
By autumn in both years, the HYG/SMR colonies had significantly fewer mites on adult bees and in worker brood compared to the control colonies and the HYG colonies had intermediate mite populations. Contrary to expectation, there were no differences among the lines in mite reproductive success. Further studies are required to determine if the genes and neural mechanisms that regulate the SMR trait are the same or different from those regulating hygienic behavior. We have just published a paper on these results:
Ibrahim, A., Reuter, GS, Spivak, M. 2007. Field trial of honey bee colonies bred for mechanisms of resistance against Varroa destructor. Apidologie 38: 67-76
Objective 3. When we have completed all the sampling and analysis for Objective 1, we will be able to develop published guidelines for migratory beekeepers on making educated treatment decisions for the mite based on the sampling plan. Also, at every beekeeping association meeting Spivak and Reuter attend, we talk to beekeepers about the importance of sampling plans and how they will improve the profit margins of their operations by not having to treat as often or extensively. We have received very favorable feedback and many say they are anxiously anticipating our results.
Impacts and Contributions/Outcomes
The North Central region of the US, particularly MN, ND and SD are the top honey producing states based on yield per colony, together producing over 30% of the total honey production for the nation. The reduction in pesticide use by beekeepers will increase the profitability of beekeeping, which is based on small and moderate-scale owner-operated farms, improve the quality of honey, a wholesome food product, and improve environmental quality by promoting honey bees, vital pollinators of our agro- and natural ecosystem.