Quantitative trait loci mapping for survival of virus infection and virus levels in honey bees.

Israeli acute paralysis virus (IAPV) is a highly virulent, Varroa-vectored virus that is of global concern for honey bee health. Little is known about the genetic basis of honey bees to withstand infection with IAPV or other viruses. We set up and analyzed a backcross between preselected honey bee colonies of low and high IAPV susceptibility to identify quantitative trait loci (QTL) associated with IAPV susceptibility. Experimentally inoculated adult worker bees were surveyed for survival and selectively sampled for QTL analysis based on SNPs identified by whole-genome resequencing and composite interval mapping. Additionally, natural titers of other viruses were quantified in the abdomen of these workers via qPCR and also used for QTL mapping. In addition to the full dataset, we analyzed distinct subpopulations of susceptible and non-susceptible workers separately. These subpopulations are distinguished by a single, suggestive QTL on chromosome 6, but we identified numerous other QTL for different abdominal virus titers, particularly in the subpopulation that was not susceptible to IAPV. The pronounced QTL differences between the susceptible and non-susceptible subpopulations indicate either an interaction between IAPV infection and the bees' interaction with other viruses or heterogeneity among workers of a single cohort that manifests itself as IAPV susceptibility and results in distinct subgroups that differ in their interaction with other viruses. Furthermore, our results indicate that low susceptibility of honey bees to viruses can be caused by both, virus tolerance and virus resistance. QTL were partially overlapping among different viruses, indicating a mixture of shared and specific processes that control viruses. Some functional candidate genes are located in the QTL intervals, but their genomic co-localization with numerous genes of unknown function delegates any definite characterization of the underlying molecular mechanisms to future studies.

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

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.

Foraging and homing behavior of honey bees (Apis mellifera) during a total solar eclipse.

Exceptional natural phenomena, such as those that occur during a total solar eclipse, provide unique opportunities to study animal behavior outside the naturally evolved context, which can be informative in more general terms. Circumstantial descriptions of abnormal animal behavior during solar eclipses abound, although scientific studies conducted during an eclipse are relatively rare due to inherent logistical difficulties. Here, honey bee foraging and homing behavior were studied during the total solar eclipse of August 21, 2017. In the first experiment, we studied foraging behavior of honey bees during the progression of the solar eclipse and found that the foraging activity drastically decreased but did not completely cease during the totality of the eclipse, in contrast to previous reports of complete cessation. The data indicate that the level of ambient light can largely overrule the internal circadian rhythm of foraging honey bees. Furthermore, colonies with a higher need for foraging decreased their foraging activity less than satiated colonies, consistent with the hypothesis that individual foraging decisions may be influenced by colony state, which affects cost-benefit analyses. In a second experiment, the temporal dynamics of homing of released workers and drones was compared in periods before, during, and after the solar eclipse. During the totality of the eclipse, very few bees arrived back at their hive, while homing before the total eclipse was accelerated, particularly in drones. The results suggest that, while the homing abilities of honey bees are not compromised until the sun is completely eclipsed, they may still interpret the diminishing light as an indicator of deteriorating flight conditions. Our unique study provides some insight into the control of honey bee foraging behavior when external cues and internal circadian rhythms are at odds, lent support to the notion that food deprivation can lead to riskier foraging, and indicated that homing in honey bees is possible even with very small amounts of sunlight.