Submitted to: American Bee Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: January 13, 2007
Publication Date: May 1, 2007
Citation: Villa, J.D. 2007. Intermediate Levels of Resistance to Tracheal Mites in Crosses Between Resistant and Susceptible Strains. American Bee Research Conference Proceedings. American Bee Joournal 147(5):442 Technical Abstract: Bioassays and sampling of field colonies were used to test the hypothesis that the resistance to tracheal mites in Russian honey bees is a dominant trait. Earlier studies with Buckfast bees as a resistant parent had suggested dominance or partial dominance in their crosses with either a Canadian susceptible line (Lin et al., 1996, Exp. Appl. Acarol. 20: 87-101) or with U. S. sources (Danka & Villa, 2001, J. Econ. Entomol. 93: 1602-1605). Starting in 2003, colonies of Russian origin (R X R) and from selected susceptible colonies in the U.S. (S X S) were propagated using instrumental insemination and further selected for diverging levels of tracheal mite resistance. Five groups of F1 colonies were produced by crossing queens and drones from these diverging parental colonies in spring or autumn (2003-2006). In a series of 10 bioassays, 20-50 young workers (< 12 h from emergence) from surviving R X R, F1 and S X S colonies were simultaneously introduced into infested colonies and retrieved five to seven days later. On average, each bioassay tested 3.5 R X R, 4.7 F1, and 3.3 S X S colonies coming from a total of 21, 26, and 26 colonies, respectively. Average mite abundance (female mites per worker) was calculated for each colony in each bioassay and used as the variable for analyses. In July 2005, a group of 27 R X R, 17 F1 and 28 S X S queens were randomly assigned to colony divisions and established in two apiaries near Baton Rouge, Louisiana. Initial colony infestation was highly variable but evenly distributed between the three groups. Colonies were sampled and the queen status checked bimonthly until May 2006. The average mite abundance of F1 colonies averaged over all bioassays was intermediate (0.96 ± 0.15, mean ± SE), and significantly different from that of both R X R colonies (0.63 ± 0.15) and S X S colonies (1.37 ± 0.15). However, when results for the ten bioassays are analyzed individually, the infestation of F1 colonies gives variable outcomes: in five of the ten bioassays, the F1 colonies were similar to the R X R and significantly different from the S X S colonies, in two bioassays, the F1 colonies were similar to the S X S colonies, in one bioassay the F1 colonies were intermediate, and in two bioassays there were no significant differences between the groups. In 17 field colonies surviving with original queens after 10 months, tracheal mite infestation was highly variable, with many colonies showing no detectable levels of infestation. Nevertheless, mite prevalences in colonies showed distributions supporting the findings of the bioassay. All three resistant colonies had undetectable mite levels while prevalences in 4 F1 colonies ranged from 0% to 53%, and prevalences in 10 S X S colonies ranged from 0% to 90%. These data sets do not support the hypothesis that a single dominant gene confers resistance to Russian bees. The trait most likely is regulated by a number of additive genes.