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The constant pressure posed by parasites has caused species throughout the animal kingdom to evolve suites of mechanisms to resist infection. Individual barriers and physiological defenses are considered the main barriers against parasites in invertebrate species. However, behavioral traits and other non-immunological defenses can also effectively reduce parasite transmission and infection intensity. In social insects, behaviors that reduce colony-level parasite loads are termed \"social immunity.\" One example of a behavioral defense is resin collection. Honey bees forage for plant-produced resins and incorporate them into their nest architecture. This use of resins can reduce chronic elevation of an individual bee's immune response. Since high activation of individual immunity can impose colony-level fitness costs, collection of resins may benefit both the individual and colony fitness. However the use of resins as a more direct defense against pathogens is unclear. Here we present evidence that honey bee colonies may self-medicate with plant resins in response to a fungal infection. Self-medication is generally defined as an individual responding to infection by ingesting or harvesting non-nutritive compounds or plant materials. Our results show that colonies increase resin foraging rates after a challenge with a fungal parasite (Ascophaera apis: chalkbrood or CB). Additionally, colonies experimentally enriched with resin had decreased infection intensities of this fungal parasite. If considered self-medication, this is a particularly unique example because it operates at the colony level. Most instances of self-medication involve pharmacophagy, whereby individuals change their diet in response to direct infection with a parasite. In this case with honey bees, resins are not ingested but used within the hive by adult bees exposed to fungal spores. Thus the colony, as the unit of selection, may be responding to infection through self-medication by increasing the number of individuals that forage for resin.

Hygienic behaviour is a social immune response in honey bees shown to help provide resistance to honey bee pests and diseases. A survey of hygienic behaviour and brood diseases was conducted on 649 colonies in eastern Australia to initiate a selective breeding program targeting disease resistance and provide a level of resistance to Varroa (Varroa destructor Anderson and Trueman and V. jacobsoni Oudemans) mites should they become established in Australia. The test population showed a remarkably high baseline level of hygienic behaviour with 17% of colonies meeting or exceeding breeding selection thresholds. Colonies belonging to a breeding program were 5.8 times more likely to be highly hygienic and colonies headed by queens raised from hygienic queen mothers were 2.2 times more likely. Nectar availability (nectar yielding flowering plants within honey bee forage range) influenced hygienic behaviour expression but was not a significant predictor of level of hygienic behaviour. Surprisingly, hygienic behaviour was not a significant predictor of the presence of infection of the honey bee brood disease chalkbrood (Ascosphaera apis) and was not influential in predicting severity of chalkbrood infection in surveyed honey bee colonies. This study, along with reports from commercial beekeepers that chalkbrood infection is on the rise, warrants a deeper exploration of the host-pathogen relationship between Apis mellifera and Ascosphaera apis in Australia.

To improve health and vitality of honey bees ( Apis mellifera ) beekeepers can propagate stocks that demonstrate resistance to both parasites and pathogens. Most breeding programs focus on resistance to Varroa destructor mites and/or brood pathogens. Colonies bred specifically for the trait Varroa Sensitive Hygiene (VSH), exhibit a high level of resistance to the parasitic mites. Still, they have never been explicitly tested for resistance to brood diseases. The goal of this study was to test if colonies bred for VSH are both mite and disease resistant. Over two years (2023 and 2024) and in two locations (University of Minnesota and the USDA-ARS lab in Baton Rouge, Louisiana), we compared colonies from the Pol-line bred specifically for VSH to colonies from a commercial source. The Commercial colonies in this study were not selected specifically for Varroa resistance but were selected for “general” hygienic behavior using the freeze-killed brood (FKB) assay. We challenged colonies within each line with Ascosphara apis, a fungus that causes chalkbrood, and quantified mites, disease and hygienic behavior. Our study demonstrated that bees from the Pol-line bred for VSH are just as resistant to chalkbrood as bees from a commercial line bred for hygienic behavior. Results confirmed that the Pol-line was more mite resistant than the Commercial, as it had significantly lower mites in two of three trials. Both the Pol-line and Commercial colonies had high levels of hygienic behavior. These results indicate that VSH-selected honey bees respond to both mite-infested and disease-infected brood. Further comparative studies are needed to clarify any differences in genetic mechanisms and olfactory sensitivity mediating the VSH-trait and general hygienic behavior. On a practical level, using honey bees selected for VSH in beekeeping operations could help curb losses, improve honey bee health, and reduce financial burdens caused by Varroa and diseases.

Swarming, or colony reproduction, in honey bees ( Apis mellifera ) is an indicator of colony-level fitness. The drivers of swarming remain elusive at both the colony and individual bee level. Floral abundance, rapid colony growth, and congestion are colony correlates and partial triggers of swarming but are not singularly causal. The nutritional and physiological state of individual bees within colonies preparing to swarm has been understudied. We hypothesized that vitellogenin (Vg), a phospholipoglycoprotein that influences the honey bee age-based division of labor in individual bees, might also mediate the cascade of physiological and behavioral processes that lead to reproductive swarming. Over two years, we compared vitellogenin ( Vg ) gene expression levels in age-marked worker bees sampled at various intervals before a swarm (pre-swarming colonies) to samples of same-aged bees collected from non-swarming colonies at the same time intervals. Vg levels were significantly higher in 10- and 14-day old bees from pre-swarming colonies three days prior and within 24 h of swarm issuance. Vg levels normally decrease in 10-14d old bees that are transitioning to the forager behavioral state. We provide a hypothesis for how Vg levels in individual bees might influence the colony-level regulatory processes that lead to swarming. This work may show for the first time, the link between a highly conserved protein associated with individual reproduction across oviparous animal taxa and its function as a mechanism of social reproduction in honeybees colonies.

Food quantity and macronutrients contribute to honey bee health and colony survival by mediating immune responses. We determined if this held true for bees injected with chronic bee paralysis virus (CBPV) and deformed wing virus (DWV), two common honey bee ssRNA viruses. Pollen-substitute diet and syrup consumption rates and macronutrient preferences of two Varroa-resistant stocks (Pol-Line and Russian bees) were compared to Varroa-susceptible Italian bees. Bee stocks varied in consumption, where Italian bees consumed more than Pol-Line and Russian bees. However, the protein: lipid (P:L) ratios of diet consumed by the Italian and Russian bees was greater than that of the Pol-Line bees. Treatment had different effects on consumption based on the virus injected. CBPV was positively correlated with syrup consumption, while DWV was not correlated with consumption. P:L ratios of consumed diet were significantly impacted by the interaction of bee stock and treatment, with the trends differing between CBPV and DWV. Variation in macronutrient preferences based on viral species may indicate differences in energetic costs associated with immune responses to infections impacting different systems. Further, virus species interacted with bee genotype, indicating different mechanisms of viral resistance or tolerance among honey bee genotypes.

Background The population genetics of U.S. honey bee stocks remain poorly characterized despite the agricultural importance of Apis mellifera as the major crop pollinator. Commercial and research-based breeding programs have made significant improvements of favorable genetic traits (e.g. production and disease resistance). The variety of bees produced by artificial selection provides an opportunity to characterize the genetic diversity and regions of the genome undergoing selection in commonly managed stocks. Results Pooled sequencing of eight honey bee stocks found strong genetic similarity among six of the stocks. Two stocks, Pol-line and Hilo, showed significant differentiation likely due to their intense and largely closed breeding for resistance to the parasitic Varroa mite. Few variants were identified as being specific to any one stock, indicating potential admixture among the sequenced stocks. Juxtaposing the underlying genetic variation of stocks selected for disease- and parasite-resistance behavior, we identified genes and candidate regions putatively associated with resistance regulated by hygienic behavior. Conclusion This study provides important insights into the distinct genetic characteristics and population diversity of honey bee stocks used in the United States, and provides further evidence of high levels of admixture in commercially managed honey bee stocks. Furthermore, breeding efforts to enhance parasite resistance in honey bees may have created unique genetic profiles. Genomic regions of interest have been highlighted for potential future work related to developing genetic markers for selection of disease and parasite resistance traits. Due to the vast genomic similarities found among stocks in general, our findings suggest that additional data regarding gene expression, epigenetic and regulatory information are needed to more fully determine how stock phenotypic diversity is regulated.

When wild honey bee colonies ( Apis mellifera ) nest in hollow tree cavities, they coat the rough cavity walls with a continuous layer of propolis, a substance comprised primarily of plant resins. Studies have shown that the resulting “propolis envelope” leads to both individual- and colony-level health benefits. Unfortunately, the smooth wooden boxes most commonly used in beekeeping do little to stimulate propolis collection. As a result, most managed bees live in hives that are propolis-poor. In this study, we assessed different surface texture treatments (rough wood boxes, boxes outfitted with propolis traps, and standard, smooth wood boxes) in terms of their ability to stimulate propolis collection, and we examined the effect of propolis on colony health, pathogen loads, immune gene expression, bacterial gene expression, survivorship, and honey production in both stationary and migratory beekeeping contexts. We found that rough wood boxes are the most effective box type for stimulating propolis deposition. Although the use of rough wood boxes did not improve colony survivorship overall, Melissococcus plutonius detections via gene expression were significantly lower in rough wood boxes, and viral loads for multiple viruses tended to decrease as propolis deposition increased. By the end of year one, honey bee populations in migratory rough box colonies were also significantly larger than those in migratory control colonies. The use of rough wood boxes did correspond with decreased honey production in year one migratory colonies but had no effect during year two. Finally, in both stationary and migratory operations, propolis deposition was correlated with a seasonal decrease and/or stabilization in the expression of multiple immune and bacterial genes, suggesting that propolis-rich environments contribute to hive homeostasis. These findings provide support for the practical implementation of rough box hives as a means to enhance propolis collection and colony health in multiple beekeeping contexts.

The ectoparasite Varroa destructor is the greatest threat to managed honey bee ( Apis mellifera ) colonies globally. Despite significant efforts, novel treatments to control the mite and its vectored pathogens have shown limited efficacy, as the host remains naïve. A prospective solution lies in the development of Varroa -resistant honey bee stocks, but a paucity of rigorous selection data restricts widespread adoption. Here, we characterise the parasite and viral dynamics of a Varroa -resistant honey bee stock, designated ‘Pol-line’, using a large-scale longitudinal study. Results demonstrate markedly reduced Varroa levels in this stock, diminished titres of three major viruses (DWV-A, DWV-B, and CBPV), and a two-fold increase in survival. Levels of a fourth virus that is not associated with Varroa —BQCV—do not differ between stocks, supporting a disruption of the transmission pathway. Further, we show that when decoupled from the influence of Varroa levels, viral titres do not constitute strong independent predictors of colony mortality risk. These findings highlight the need for a reassessment of Varroa etiology, and suggest that derived stocks represent a tractable solution to the Varroa pandemic.

Declines in managed honey bee populations are multifactorial but closely associated with reduced virus immunocompetence and thus, mechanisms to enhance immune function are likely to reduce viral infection rates and increase colony viability. However, gaps in knowledge regarding physiological mechanisms or ‘druggable’ target sites to enhance bee immunocompetence has prevented therapeutics development to reduce virus infection. Our data bridge this knowledge gap by identifying ATP-sensitive inward rectifier potassium (K ATP ) channels as a pharmacologically tractable target for reducing virus-mediated mortality and viral replication in bees, as well as increasing an aspect of colony-level immunity. Bees infected with Israeli acute paralysis virus and provided K ATP channel activators had similar mortality rates as uninfected bees. Furthermore, we show that generation of reactive oxygen species (ROS) and regulation of ROS concentrations through pharmacological activation of K ATP channels can stimulate antiviral responses, highlighting a functional framework for physiological regulation of the bee immune system. Next, we tested the influence of pharmacological activation of K ATP channels on infection of 6 viruses at the colony level in the field. Data strongly support that K ATP channels are a field-relevant target site as colonies treated with pinacidil, a K ATP channel activator, had reduced titers of seven bee-relevant viruses by up to 75-fold and reduced them to levels comparable to non-inoculated colonies. Together, these data indicate a functional linkage between K ATP channels, ROS, and antiviral defense mechanisms in bees and define a toxicologically relevant pathway that can be used for novel therapeutics development to enhance bee health and colony sustainability in the field.

The ongoing decline of honey bee health worldwide is a serious economic and ecological concern. One major contributor to the decline are pathogens, including several honey bee viruses. However, information is limited on the biology of bee viruses and molecular interactions with their hosts. An experimental protocol to test these systems was developed, using injections of Israeli Acute Paralysis Virus (IAPV) into honey bee pupae reared ex-situ under laboratory conditions. The infected pupae developed pronounced but variable patterns of disease. Symptoms varied from complete cessation of development with no visual evidence of disease to rapid darkening of a part or the entire body. Considerable differences in IAPV titer dynamics were observed, suggesting significant variation in resistance to IAPV among and possibly within honey bee colonies. Thus, selective breeding for virus resistance should be possible. Gene expression analyses of three separate experiments suggest IAPV disruption of transcriptional homeostasis of several fundamental cellular functions, including an up-regulation of the ribosomal biogenesis pathway. These results provide first insights into the mechanisms of IAPV pathogenicity. They mirror a transcriptional survey of honey bees afflicted with Colony Collapse Disorder and thus support the hypothesis that viruses play a critical role in declining honey bee health.