Expression levels of immune-genes in developing workers of Apis mellifera in response to reproductive timing and infestation level by the parasitic mite Varroa destructor
The parasitic mite Varroa destructor is one of the biggest health problems of the Western Honey Bee, Apis mellifera. It feeds from the bees' hemolymph and vectors several honey bee pathogens. V. destructor has also been reported to compromise honey bee immunity but available data are insufficient to support this claim. This study was designed to assess the effect of mite infestation on honey bee immune-gene expression during the biologically relevant host developmental stages. In my experiment, mites were manually introduced into honey bee larval cells at three different levels. Control groups were either left unmanipulated or wounded. Developing bees were collected with any retrievable mites daily from the experimental cells for ten days. Mite reproduction was assessed and bee hosts were analyzed for expression levels of ten immune genes using quantitative RT-PCR. This experiment showed effects of developmental time and experimental treatment on gene expression that generally contradict the previously hypothesized immunosuppression of bees by V. destructor. However, mites might temporarily suppress the honey bees' normal response to cuticle wounding based on reproductive timing. The artificial wounding group exhibited an increased viral load, suggesting that wounding may trigger or enable virus replication. Overall, my results indicate the importance of physical trauma caused by wounding and suggest complex temporal dynamics in the relationships between bee host, mite parasite, and vectored pathogens
