Variant A of the Deformed Wings Virus Alters the Olfactory Sensitivity and the Expression of Odorant Binding Proteins on Antennas of Apis mellifera

Abstract

Simple Summary Honey bees, Apis melllifera, are the most commonly managed bee in the world for pollination services. However, worldwide continuous colony losses have been reported for almost a decade. One factor of these losses is associated to pathogens being the virus one of the most important problems in honey bee health. One of the known viruses that affect the honey bee population is deformed wing virus (DWV). DWV causes physical malformation and behavioral disturbances, but also, this virus can be found in the antenna affecting the anatomical integrity of infected areas, which could compromise normal antennal functioning associated to aroma perception. Thus, we evaluate olfactory sensitivity and the expression of antenna-specific odorant-binding proteins (OBP) genes in honey bees inoculated with variant A of the DWV. We performed olfactory sensitivity analysis using the essential oils Eucalyptus globulus and Mentha piperita, but also, and molecular analysis of gene expression of nine OBPs. We found that the high level of replication of DWV-A in the antennae decreased the olfactory sensitivity and led to a down-regulation of some OBPs in middle- and forager-age worker bees. Thus, DWV-A infection in adults of honey bees could compromise volatile compound recognition inside the hive and outside the hive. Abstract Insects have a highly sensitive sense of smell, allowing them to perform complex behaviors, such as foraging and peer recognition. Their sense of smell is based on the recognition of ligands and is mainly coordinated by odorant-binding proteins (OBPs). In Apis mellifera, behavior can be affected by different pathogens, including deformed wing virus (DWV) and its variants. In particular, it has been shown that variant A of DWV (DWV-A) is capable of altering the ultra-cellular structure associated with olfactory activity. In this study was evaluated olfactory sensitivity and the expression of OBP genes in honey bees inoculated with DWV-A. Electroantennographic analyses (EAG) were carried out to determine the olfactory sensitivity to the essential oils Eucalyptus globulus and Mentha piperita. The expression of nine antenna-specific OBP genes and DWV-A load in inoculated bees was also quantified by qPCR. We observed an inverse relationship between viral load and olfactory sensitivity and the expression of some OBP proteins. Thus, high viral loads reduced olfactory sensitivity to essential oils and the gene expression of the OBP2, OBP5, OBP11, and OBP12 proteins on the antennas of middle- and forager-age bees. These results suggest that DWV-A could have negative effects on the processes of aroma perception by worker bees, affecting their performance in tasks carried out in and outside the colony.