Comparing Survival of Israeli Acute Paralysis Virus Infection among Stocks of U.S. Honey Bees

SIMPLE SUMMARY: Honey bees and other pollinators are threatened by numerous stressors, including virus infections. Currently, no effective treatments are available, stressing the importance of natural defenses. These defenses may be enhanced through selective breeding. This study sought to evaluate the potential for breeding, while also testing a few potential mechanisms of natural immune responses and assessing how widespread viruses are in commercial honey bee queens in the U.S. We identified significant differences in survival of virus infection among and within U.S honey bee stocks, indicating that selective breeding may be able to decrease the virus susceptibility of honey bees. Survival differences may be related to differences in the natural immune system of honey bees and could relate to how much virus stress bees have experienced in the past. ABSTRACT: Among numerous viruses that infect honey bees (Apis mellifera), Israeli acute paralysis virus (IAPV) can be linked to severe honey bee health problems. Breeding for virus resistance may improve honey bee health. To evaluate the potential for this approach, we compared the survival of IAPV infection among stocks from the U.S. We complemented the survival analysis with a survey of existing viruses in these stocks and assessing constitutive and induced expression of immune genes. Worker offspring from selected queens in a common apiary were inoculated with IAPV by topical applications after emergence to assess subsequent survival. Differences among stocks were small compared to variation within stocks, indicating the potential for improving honey bee survival of virus infections in all stocks. A positive relation between worker survival and virus load among stocks further suggested that honey bees may be able to adapt to better cope with viruses, while our molecular studies indicate that toll-6 may be related to survival differences among virus-infected worker bees. Together, these findings highlight the importance of viruses in queen breeding operations and provide a promising starting point for the quest to improve honey bee health by selectively breeding stock to be better able to survive virus infections.