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Title: Influence of Worker Age on the Infestation of Resistant and Susceptible Honey Bees (Apis mellifera) with Tracheal Mites (Acarapis woodi)*

item Villa, Joseph

Submitted to: Apidologie
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2007
Publication Date: 10/1/2007
Citation: Villa, J.D. 2007. Influence of Worker Age on the Infestation of Resistant and Susceptible Honey Bees (Apis mellifera) with Tracheal Mites (Acarapis woodi)*. Apidologie 38:573-578

Interpretive Summary: Honey bee colonies in the United States can be weakened severely or die when their worker bees are highly parasitized by tracheal mites. Bees imported from Russia have levels of genetic resistance to these mites sufficient to reduce infestation to harmless levels, while many other strains are very vulnerable. Parasitism of worker bees is initiated by mites invading the breathing tubes of young workers (less than 48 hours old). Experiments were conducted to compare the vulnerability of workers of different ages from two genetic origins: resistant Russian colonies and highly susceptible colonies. Workers from both strains became much less vulnerable to mites with age. At the youngest ages, Russian worker bees were invaded by fewer mites than equally aged susceptible worker bees. Mite parasitism was low in all older bees (72 to 96 hours old), regardless of their genetic origin. The large difference in infestation at a young age in Russian and susceptible workers helps understand what is required to make a colony highly resistant to mite parasitism. These findings also help optimize conditions for a rapid screening of test colonies for their potential resistance to tracheal mites.

Technical Abstract: In an earlier study, resistant and susceptible workers exposed to tracheal mites one, two, three or four days post-emergence showed a decline in infestation. I further investigated the combined effects of worker age and of strain on infestation with tracheal mites. In four separate tests, workers were aged to evenly distributed classes reaching maximum ages of 9, 24, 48 and 96 h. The following factors influenced infestation levels: (1) overall, infestation of workers from resistant colonies was significantly lower than for susceptible colonies (2) age produced parallel rates of decline in infestation in both resistant and susceptible workers in the first three tests and (3) in the test up to 96 h, the large infestation differences in the youngest workers became very similar in workers aged three or four days. The differences between strains were highest at the youngest ages in all tests, indicating that evaluations of potentially resistant colonies should use the youngest workers possible