by Keith S. Delaplane, Professor and CAP Director, University of Georgia
CAP Updates: 23
Last August the leaders of the Managed Pollinator CAP http://www.beeccdcap.uga.edu/ submitted a 96-page progress report to USDA as part of our annual renewal process. The report was followed up with an on-site interview in Washington DC between several of us and an expert panel of peer scientists who queried us on the details of our work and future plans. The upshot of all this is that we were approved for our fourth and final year of funding. The full report makes for some heavy reading, but I thought this is a good opportunity to showcase some of the emerging trends in our work. From the beginning, our emphasis has been on narrowing and better understanding the causes of bee decline. Here follow some highlights.
- We have not been able to replicate the negative European experience with Nosema ceranae. In fact, this “new” Nosema appears to be less virulent than the “old” Nosema apis which it has largely replaced. Moreover, it appears that neither Nosema synergizes with viruses to increase bee mortality.
- We have shown that the Varroa mite, present in the US since 1987, is a vector of Israeli Acute Paralysis Virus – one of the pathogens implicated in bee colony deaths. IAPV levels go up as Varroa levels go up, which turns the spotlight toward Varroa as the underlying problem.
- Our group is studying the use of RNA silencing technology to “shut off” the virulence factors associated with IAPV.
- One of our biggest investments is a coordinated national study using seven sentinel apiaries (in CA, WA, TX, MN, FL, PA, ME) in an attempt to understand factors affecting colony survival in the field – parasite and disease levels, environmental toxins, weather, land use patterns, and their interactions. These data are used to populate computer models that help us identify single factors, or interactions, that most powerfully predict colony collapse. This has generated some surprises. For example, bee mortality is negatively impacted as the percentage land use in agriculture increases, but this is not associated with any identifiable trend in pesticide use. Speaking of pesticides, national sampling of bee-collected pollen has revealed 130 different residues of pesticides or pesticide metabolites. The average number of residues per bee pollen load is 6.2! But tracing these levels to actual bee mortality has been difficult, and so far only weakly associated with higher rates of queen supersedure. In general, this data set is showing the preeminence of Varroa mite, corroborating our lab studies above. High levels of Varroa are associated with high levels of virus and low populations of adult bees and brood.
- We have shown a high degree (73-93%) of cross-infection of viruses between honey bees and local native bumble bees. Thus the possibility exists for complicated infection > reinfection pathways in nature.
- Our group has shown the possibility for dangerous (to bees) chemical interactions between agricultural fungicides and two of the most commonly used miticides beekeepers use to control Varroa mite – coumaphos and fluvalinate. This poses a dilemma – our data clearly underscore the importance of controlling Varroa mite – but the remedial chemicals available to beekeepers to control the mite are themselves hazardous if they combine with other environmental toxins.
- Our group has identified neonicotinoid seed treatments of annual crops as an acute toxic threat to insect pollinators, particularly in the context of dust exposure associated with treated corn seed at spring planting. These compounds become systemic in plants, persist in the environment, and are lethal to bees at the level of parts per billion. Dust released from planters during spring planting has been shown to express concentrations of pesticide one million times higher than that – at the level of parts per thousand.
- However, when pesticides are viewed in the aggregate at the national level, residues of pyrethroids – a large class of traditional pesticides and “older” chemistry – pose a 3-fold greater hazard to the colony than neonicotinoids, based on mean and frequency of detection in pollen samples and relative acute toxicity.
- In pursuit of non-chemical answers to the Varroa mite, our team is working on the genetic basis of honey bee disease and parasite resistance. One team is working on the genetic basis of “grooming behavior” where bees clean themselves of Varroa mite and “hygienic behavior” where bees identify brood cells containing mites and remove them. Combining these traits should increase mite resistance. Another group is working to enlarge the genetic diversity available to bee breeders by importing germplasm from the honey bee’s native range in eastern Europe. And finally a third group has initiated a Bee Team to assist the California Bee Breeders with on-site stock selection for disease and mite resistance.
- The information arm of our CAP has focused on publishing a Best Management Practices guide, educational videos, and health bulletins for beekeepers at the eXtension.org site – a repository of peer-reviewed, credible scientific information at http://www.extension.org/bee_health
If our CAP has reached any one overarching conclusion, it is that “bee decline” is a huge issue and not easily reducible to one or a few “causes.” It is instead a web of causation, and the answer will involve not only good bee husbandry, but revisions to our land use and pest control habits.