Improving honey Bee Health and Pollination Sustainability with Mite-Resistant Bees

Improving honey Bee Health and Pollination Sustainability with Mite-Resistant Bees

Summary

We continued selection and breeding of bees for resistance to Varroa mites. Significant progress was made in both research and extension activities. Descriptions of the breeding program and new methods to select for increased mite-grooming behavior were published in the two major US beekeeping trade journals, in two articles in an international apicultural research journal, and on the honey bee health eXtension website. In the fall of 2010, mite-grooming behavior of our colonies was measured as the proportion of chewed mites falling from bees. The mite populations in those colonies were inversely correlated with the proportion of chewed mites, indicating that the behavior is having a significant impact on mite populations. Three-day queen-rearing workshops were offered at Purdue University and at the Heartland Apicultural Society conference. Beekeepers purchased queens from our mite-tolerant stocks and they were used in our cooperators hives (~3000 colonies).

Objectives/Performance Targets

There were four objectives in the original proposal.

1) Increase mite-grooming traits in the Purdue honey bee breeding program.
2) Demonstrate the benefits of breeding for resistance to Varroa mites.
3) Promote the use of resistant stock by training Midwest beekeepers in how to raise queens.
4) Incorporate both VSH and grooming behavior traits in stocks.

Accomplishments/Milestones

Increased mite-grooming behavior was demonstrated in 2010. The maximum proportion of mutilated mites falling from the nest was 20-25%, as compared to 8% when the program was inititated. Both of these measurements were done in the fall. However, we have unpublished data that suggest a seasonal effect on grooming behavior. This year we will test to see if there is a higher level of mite grooming in June, which may increase our ability to measure this trait and increase our response to selection. Instrumental inseminations between high mite-grooming colonies were performed last year to accelerate breeding for this trait.

In late 2009, we developed a new lab assay for measuring grooming behavior and showed that it correlated with the proportion of chewed mites in colonies. Bees with the least mites on adults at the beginning of the assay also removed the highest proportion of mites in the lab (Andino and Hunt, In Press; p<0.01), indicating that grooming correlated with reduced mite loads on adult bees. These results were also reported at the national meetings and appear on the honey bee health eXtension website. In 2010, we found that the proportion of chewed mites in 73 colonies was inversely correlated with mite populations, showing that grooming behavior is a significant factor reducing mite populations in our hives (p<0.05; unpublished data).

We set up two remote apiaries of 30 colonies each that were re-queened half with stock from our selection program and half with commercial stock (from three sources). Unfortunately, mite levels were very high in these 60 hives and both apiaries experienced very high winter kills (67% overall). In contrast, the winter losses in the other 105 colonies in the selection program were moderate. We lost 30% at the bee lab apiary and 19% in our mating yard that contains our elite selections. A survey of about 600 hives in north central Indiana showed 52% losses this winter. We maintain high mite levels in our colonies to aid in selection but this practice also increases our losses. Colonies that died had about 50% higher mite levels in the fall than did colonies that survived. In the two hardest hit trial apiaries, the more susceptible commercial colonies may have sustained higher mite populations, which could have then infested nearby mite-tolerant hives. We will repeat this trial of commercial versus selected stocks this season by requeening the hives and measuring winter survival.

The breeding program was described at eight beekeeper meetings (one national, two regional/out-of-state). Two, three-day queen-rearing shortcourses were offered to sixty beekeepers; one course was offered at Purdue University and another was offered at the Heartland Apiculture Society meeting in Tennessee. So far this project has trained 90 beekeepers how to raise their own queens. The breeding program was described in articles published in both of the major US beekeeping trade journals, and also in a review article in a scientific journal (Hunt 2010a,b; Rinderer et al. 2010). Last year approximately 500 queens from the program were sold by our collaborators. In 2011, collaborator Dave Shenefield obtained a grant through the Indiana State Department of Agriculture to help train beekeepers in queen rearing and to make queen cells and mated queens from the Purdue breeding program generally available to beekeeping associations and clubs in the Midwest, focusing on Indiana. The goal is to distribute 1,500 queens this season. In addition, instrumental insemination devices will be purchased and workshops on their use will be conducted. At the 10th annual Heartland Apiculture Society conference held in Indiana this summer we will offer concurrent queen rearing classes and workshops on selecting for mite resistance. The project director is this year’s chairman for HAS and the theme will be “helping bees to help themselves: breeding healthy bees”.

We have not yet made crosses between high VSH lines and high grooming-behavior lines because we first wanted to increase the grooming trait. We have VSH lines available and expect to make the first such crosses this final year of the project. There is still a lot of room for stock improvement. We will seek further funding to continue this project.

Impacts and Contributions/Outcomes

Varroa mites continue to have the greatest impact on honey bee mortality (Hunt 1998; Currie et al. 2010; Dahle 2010; Guzmán-Novoa et al. 2010; Peterson et al. 2010). Mite-grooming behavior and Varroa-specific hygiene (VSH) are the two traits that have been documented as having the biggest impact on controlling Varroa mite populations in bee hives. The USDA bee lab in Baton Rouge has successfully bred bees for high VSH levels and made the stocks commercially available. To our knowledge, ours is still the only breeding program working on mite-grooming behavior in the US. We have developed methods to assay for mite-grooming behavior, increased levels of the trait in our bee stocks, and have shown that the trait does reduce mite populations.

More beekeepers (90) have been trained to rear their own queens by this project. This ability will allow Midwest beekeepers develop and maintain stocks that can survive cold winters and can better tolerate the mites. Stocks from the breeding program have been made generally available and beekeepers are learning how to perform their own selection for mite resistance. The expected outcome from these activities is better winter survival and reduced use of pesticides in bee hives.

Andino G, Hunt GJ, 2011. A scientific note on a new assay to measure mite grooming behavior in honey bees. Apidologie, In Press.

Currie RW, Pernal SF, Guzmán-Novoa E 2010. Honey bee colony losses in Canada. J Apic Res 49:104-106.

Dahle, B 2010. The role of Varroa destructor for honey bee colony losses in Norway. J Apic Res 49:124-125.

Guzmán-Novoa E, Eccles L, Calvete Y, McGowan J, Kelly PG, Correa-Benítez A 2010. Varroa destructor is the main culprit for the death and reduced populations of overwintered honey bee (Apis mellifera) colonies in Ontario, Canada. Apidologie 41:443-450.

Hunt GJ, 1998. The war against Varroa: How are we doing? Am. Bee J. 138:372-374.

Hunt GJ, Breeding bees for resistance to parasites and diseases. 2010a. Am Bee J 150(7):667-669.

Hunt GJ, Breeding bees for resistance to parasites and diseases. 2010b. Bee Culture.

Peterson M, Gray A, Teale A 2010. Colony losses in Scotland in 2004-2006 from a sample survey. J. Apic. Res. 48:145-146.

Rinderer TE, Harris JE, Hunt GJ, de Guzman LI. 2010. Breeding for resistance to Varroa destructor in North America. Apidologie 41:409-424.

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