1a. Objectives (from AD-416):
Provide an assessment of the relative resistance/susceptibility of 7 lines of Australian honey bees in comparison to ARS resistant stock. The project will inform decisions about preparing for Varroa in Australia, including whether to fund an indigenous bee breeding program or to reinstate the importation of queen bees to Australia. The project may lead to the sale of United States queen bees to Australia.
1b. Approach (from AD-416):
In November 2010, in Kansas, 250 commercial colonies will be manipulated to standardize their mite populations. This will be done by 1) Equalizing colony strength, 2) Heavily treating colonies with multiple miticides. To obtain Australian stock for evaluation, Australian queen breeders will be asked to provide 20 sister queens reared by their standard procedures. Where possible, queens will be control mated. Each group of 20 sisters will constitute a ‘line’ for the purposes of the study. Queens will be mailed to the University of Sydney where they will be clipped and given a unique tag before shipping. The Australian queens (n = 20 per line) will be sent to Baton Rouge in March 2011 and introduced to the Varroa-standardized colonies. American queens of three lines (Varroa-Sensitive Hygiene – VSH, Russian and standard U.S. commercial; n = 20 per line) will be introduced simultaneously. Queens will be randomly allocated to colonies. Colonies will be visually inspected in May, July, September and November 2011, and the population of Varroa evaluated for each colony by standard techniques (de Guzman et al. 2007). Evaluations will be performed without knowledge of each queen’s origins (including the U.S. queens). Mean mite population growth will be compared among breeding lines using ANOVA.
3. Progress Report:
The potential impact of Varroa (V.) destructor on Australian beekeeping and agriculture depends in part on the levels of resistance to this parasite expressed by Australian commercial honey bees. The responses of seven lines of Australian honey bees to varroa were compared to the responses of a stock of Italian honey bees from the United States known for its susceptibility to varroa and two stocks known for their resistance to varroa, Russian honey bees (RHB) and a stock expressing the Varroa Sensitive Hygiene trait (VSH). The experiment began in May with uniform colonies having uniform infestation varroa. Varroa infestations measured as the percentage of adult bees infested in the Australian lines and the Italian stock rose from less than 10% in August to over 25% in October. From August to November, 44% of both the Australian and Italian colonies died while strongly exhibiting symptoms of Parasitic Mite Syndrome. In contrast, RHB and VSH colonies displayed comparative resistance to (V.) destructor. Their infestation rates rose from about 5% in August to 10% (RHB) and 14% (VSH) in October. Likely some of this increase resulted from invasion pressure by mites from the dying Australian and Italian colonies. During the August to November period, 4.4% of the RHB and 14.3% of the VSH colonies died. In comparisons of the seven Australian lines, only non-significant and trivial differences were found for infestation and mortality rates. All Australian lines were highly susceptible to V. destructor. Additionally, evaluations of rates of Nosema (N.) ceranae infections were made throughout the course of the experiment. Although high levels of infection were found across all stocks and lines, no stock or line exhibited an adverse effect from N. ceranae infection.