Abstract
BackgroundThe Western honey bee (Apis mellifera L.) is a critical component of human agriculture through its pollination activities. For years, beekeepers have controlled deadly pathogens such as Paenibacillus larvae, Nosema spp. and Varroa destructor with antibiotics and pesticides but widespread chemical resistance is appearing and most beekeepers would prefer to eliminate or reduce the use of in-hive chemicals. While such treatments are likely to still be needed, an alternate management strategy is to identify and select bees with heritable traits that allow them to resist mites and diseases. Breeding such bees is difficult as the tests involved to identify disease-resistance are complicated, time-consuming, expensive and can misidentify desirable genotypes. Additionally, we do not yet fully understand the mechanisms behind social immunity. Here we have set out to discover the molecular mechanism behind hygienic behavior (HB), a trait known to confer disease resistance in bees.ResultsAfter confirming that HB could be selectively bred for, we correlated measurements of this behavior with protein expression over a period of three years, at two geographically distinct sites, using several hundred bee colonies. By correlating the expression patterns of individual proteins with HB scores, we identified seven putative biomarkers of HB that survived stringent control for multiple hypothesis testing. Intriguingly, these proteins were all involved in semiochemical sensing (odorant binding proteins), nerve signal transmission or signal decay, indicative of the series of events required to respond to an olfactory signal from dead or diseased larvae. We then used recombinant versions of two odorant-binding proteins to identify the classes of ligands that these proteins might be helping bees detect.ConclusionsOur data suggest that neurosensory detection of odors emitted by dead or diseased larvae is the likely mechanism behind a complex and important social immunity behavior that allows bees to co-exist with pathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-014-1193-6) contains supplementary material, which is available to authorized users.
Highlights
The Western honey bee (Apis mellifera L.) is a critical component of human agriculture through its pollination activities
Prior to the experiments aimed to evaluate protein expression patterns and to identify hygienic behavior (HB) markers, we performed a small selective breeding program to confirm that social immunity traits, HB, could be enriched in our apiaries based on field testing
Since protein expression can be influenced by environment and the technology for measuring proteins has lagged behind tools for measuring nucleic acids, protein markers has often been ignored in favor of QTLs or SNPs for marker-assisted selection for breeding purposes
Summary
The Western honey bee (Apis mellifera L.) is a critical component of human agriculture through its pollination activities. Beekeepers have controlled deadly pathogens such as Paenibacillus larvae, Nosema spp. and Varroa destructor with antibiotics and pesticides but widespread chemical resistance is appearing and most beekeepers would prefer to eliminate or reduce the use of in-hive chemicals While such treatments are likely to still be needed, an alternate management strategy is to identify and select bees with heritable traits that allow them to resist mites and diseases. These include the economic cost of the treatments themselves, concerns around the potential contamination of hive products [6], widespread antibiotic [7] and acaricide resistance [8,9,10,11], and concerns over the effectiveness of chemotherapy for controlling Nosema spp [12] These pathogens are on a path akin to a chemical treadmill whereby resistance develops within a few years of the initial use of a particular chemical [13]. Spivak and Gilliam observed over ten years ago that acaricides and antibiotics were no longer effective against Varroa and Paenibacillus larvae [14]
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