The salivary gland transcriptome of Varroa destructor reveals suitable targets for RNAi-based mite control

The mite Varroa destructor has a dramatic impact on beekeeping, and is one of the main causes of honey bee colony losses. This ectoparasite feeds on honey bees’ liquid tissues through a wound created on the host integument, which determines weight loss, a reduced lifespan and the transmission of viral pathogens. However, despite its importance, the mite feeding strategy and the host regulation role by the salivary secretions have been poorly explored. Here we contribute to fill this gap by identifying the salivary components of V. destructor and by studying their on mite feeding and survival. Our differential expression analysis identified 30 salivary gland genes encoding putatively secreted proteins, among which only 15 were found to be functionally annotated. These latter include proteins with putative antibacterial, antifungal, cytolytic, digestive and immunosuppressive function. To study the role of the identified genes on mite feeding we selected the three most highly transcribed genes coding for: a chitin-binding domain protein (CHIBIN), a Kazal domain serine protease inhibitor (KAZAL) and a papain-like cysteine protease (PAPA). Knockdown of CHIBIN was associated with a significant decrease of mite survival, likely interfering with the immune reaction to facilitate mite feeding. This work expands our knowledge of the host regulation and nutritional exploitation strategies adopted by ectoparasites of arthropods and allows the identification of novel targets for RNAi-based strategies  of Varroa mite control.