- Agronomic: canola, cotton, rapeseed, sunflower, hay
- Fruits: apples, apricots, avocados, berries (other), cherries, berries (cranberries), citrus, melons
- Vegetables: beans, beets, broccoli, cabbages, carrots, cauliflower, celery, cucurbits, greens (leafy), lentils, onions, peppers, tomatoes, brussel sprouts
- Animals: bees
- Animal Production: parasite control, preventive practices, feed/forage
- Education and Training: extension, on-farm/ranch research, participatory research
- Pest Management: field monitoring/scouting, genetic resistance
- Sustainable Communities: public participation, urban/rural integration, sustainability measures
The incorporation of the trait, Suppression of Mite Reproduction (SMR), into our line of honey bees bred for hygienic behavior significantly reduced infestation of Varroa destructor mites within two commercial beekeeping operations relative to the pure hygienic line and a control line. We demonstrated that the mechanism of SMR is through adult bee removal of pupae on which mites are reproductively successful, more so than through physiological suppression of mite reproduction by bee pupae. We are developing a web-based course for beekeepers that emphasizes treating colonies for diseases and mites only as a last resort.
The research and extension program in apiculture at the University of Minnesota is the only one in a five state area (MN, WI, IA, SD, ND). Yet, MN, SD, and ND, are the top honey producing states in the nation based on yield per colony (National Ag. Statistics Service, 2004) and produce over 30% of the total honey production for the nation. The majority of the commercial beekeepers in the Upper Midwest are “migratory,” meaning that they transport their colonies every winter either to southern states where they produce bulk bees and queens for sale, or to CA where the bees pollinate almond and citrus orchards. The beekeepers transport their colonies back to the Upper Midwest for the summer to produce large honey crops.
The number of bee colonies and beekeepers is steadily declining due to the introduction of V. destructor into the U.S. in 1987, which kills bee colonies within 1-2 years if left untreated. To control this mite, beekeepers have been using pesticides (pyrethroids and organophosphates) within their colonies. However, the mites have developed resistance to these compounds. This use of pesticides in honey bee colonies has added an enormous operating expense to beekeepers, and risks contaminating honey and beeswax with pesticide residue.
Since 1994, we (M. Spivak and G. Reuter) have been breeding honey bees for resistance to diseases and V. destructor. The most devastating disease of honey bees is American foulbrood (AFB), a bacterial disease of brood (larvae) caused by Paenibacillus larvae. We have demonstrated that honey bees bred for hygienic behavior, a genetic trait, demonstrate good resistance to AFB and also to a fungal disease, chalkbrood (Spivak and Reuter, 2001a). Hygienic bees are able to detect, uncap, and remove disease-infected brood from the nest before the causative organisms reach the infectious stage, and before the human eye can detect clinical symptoms of disease (Woodrow and Holst, 1942; Rothenbuhler, 1964). Removing the disease in the non-infectious stage prevents it from spreading throughout the colony. We have found that bees bred for hygienic behavior also display resistance to V. destructor because they are able to detect and remove brood infested with the mites (Spivak, 1996). This mite parasite alternates between feeding on hemolymph (blood) of adult bees, and feeding and reproducing on the pupal stage of bees. Bees that remove mite-infested pupae from the nest interrupt the reproductive cycle of the mite by eliminating the progeny of the mite developing within a wax-sealed cell. To select colonies for hygienic behavior, we have used a “freeze-killed brood” assay. This assay involves recording the time it takes a colony to uncap and remove pupae that have been freeze-killed; colonies that remove over 95% of the dead brood within 48 hours are considered hygienic, and daughter queens are propagated from them (Spivak and Downey, 1998). This is an indirect assay that is correlated with rapid removal of diseased and mite-infested brood. Hygienic behavior is only one of several mechanisms of resistance to the mites (Boecking and Spivak, 1999), and bees selected for this trait on the basis of a freeze-killed brood assay do not have sufficient resistance to maintain colonies under the estimated economic treatment threshold (Spivak and Reuter, 1998; 2001b).
Since 2001, and with support from NCR-SARE, we have been incorporating another trait into our “MN Hygienic” line to increase the degree of resistance to V. destructor. The trait is “SMR” or Suppression of Mite Reproduction (Harbo and Hoopingarner, 1997; Harbo and Harris 1999a; b). In breeding for this trait, J. Harbo found colonies in which the mites had very low reproductive success on worker brood, determined by examining the brood just prior to the bees’ emergence from the cell as an adult. Colonies were found in which the mites either did not initiate egg-laying, or laid eggs too late for mite offspring to reach maturity and mate. These colonies provided the genetic basis for his intense selection and breeding program. We tested hybrid crosses between Harbo’s SMR line and our MN Hygienic line with the aim of increasing mite resistance through the SMR trait, while maintaining the high degree of disease resistance, high honey production, good brood viability, and nice temperament of the Hygienic line.
When we began this research, it was not known what mechanism was underlying the SMR trait. Originally, we hypothesized that the mechanism for Suppression of Mite Reproduction was due to behavioral incompatibilities between the mite and the bee larva during the first 12-24 hours after the bee larva is capped with wax which preclude the mite from initiating oogenesis (egg development), based on research by Donze and Guerin (1994). In the course of our investigations, we observed that the SMR line also expressed hygienic behavior. From this surprising finding, we developed a new working hypothesis, which we tested and which yielded very interesting results. The new hypothesis and results are given under Objectve 2.
We are adamant in our outreach efforts that breeding for resistance is the foundation for all alternative control measures because resistant bees require fewer treatments to control diseases and mites. Our hope is to begin to change the traditional mindset from applying a “quick fix” to emerging problems (e.g., applying a different pesticide when the mites develop resistance to the currently used one) by encouraging beekeepers to adopt the more sustainable approach of maintaining lines of bees that have their own defenses against parasites and diseases. To this end, we have begun developing a web-based course, which will provide continued, interactive instruction to beekeepers on how to breed for resistance with the goal of reducing or eliminating the use of chemical controls. To our knowledge, this is the first on-line course of its kind. We completed the front-end and one module of the course, and recently we sent it to various beekeepers and extension educators to obtain their feedback and suggestions before developing the rest of the course. The temporary link to this course, and feedback to date, is given under Objective 3 and in the Publications and Outreach section of this report, below.
Our goal is to breed honey bees, Apis mellifera, resistant to diseases and parasitic mites to reduce the amount of antibiotic and pesticide used in bee colonies, and to ensure that our breeding methods and stock are accessible to beekeepers everywhere.
Our first objective is to test hybrid crosses between a line of bees resistant to disease (bees bred for hygienic behavior) and a line resistant to the parasitic mite Varroa destructor (bees bred for “Suppression of Mite Reproduction” or SMR). Our previous research indicated that bees bred for hygienic behavior are only partially resistant to these mites. Thus, our aim is to increase the level of mite resistance while retaining the disease resistance and high honey production of the hygienic line. The crosses will be tested both in apiaries at the University of Minnesota and in apiaries owned by Mr. Darrel Rufer, a commercial beekeeper based in Minnesota.
Our second objective is to determine how bees selected for SMR are able to suppress the reproduction of the mite. We will test the hypothesis that there are behavioral incompatibilities between the mite and the bee larva during the first 12-24 hours after the bee larva is capped with wax which preclude the mite from initiating oogenesis (egg development).
Our third objective is to develop an interactive web-based course on sustainable methods of controlling diseases and mite pests of honey bees. The main emphasis will be on promoting the use of resistant bee stocks as the foundation for integrated pest management strategies. This will be the only such course available on-line to beekeepers, and is a crucial link between our research and its successful implementation.