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Nanoparticle-Shielded dsRNA enhance the stability of dsRNA in the honeybee, Apis mellifera
The ectoparasitic mite, Varroa destructor is one of the most destructive pests of the honeybee (Apis mellifera) leading to the collapse honey bee colony in many regions of the world. RNA interference (RNAi) is a novel approach recently proposed for insect pest control. However, the efficiency of RNAi in insects is low due to the lack of effective delivery methods for dsRNA and sensitivity to nuclease degradation. Therefore, the success of RNAi technology largely depends on the stability of dsRNA. To explore the possibility of using RNAi to control varroa mite, we determined the effects of dsRNA targeting a subunit of the cytoplasmic coatomer protein complex B2, D, and E subunits on target gene expression for varroa mite. We observe that dsRNA ingested by bees is transferred to the varroa mite, resulting in knockdown of COPB2 expression. Furthermore, we demonstrate that chitosan nanoparticles-dsRNA complexes were more stable for 7 days in honeybee tissue fluids. The dsRNA-conjugated with chitosan was protected from degradation in hemolymph, fat body, and midgut extracts collected from the honeybee. These results possibly suggest that nanoparticles-dsRNA complexes might be horizontally transferred from treated honeybee to varroa mite, in which case the honeybees could serve as RNAi vectors. We confirmed, moreover, dsRNA fed nontarget insects, honeybee, were unaffected, and no toxicity was observed for honeybee. Overall, these data suggest that dsRNA-conjugated with chitosan help escape effectively from degradation by honeybee tissue fluids and could improve RNAi efficiency in varroa mite.
