Double-stranded RNA reduces growth rates of the gut parasite Crithidia mellificae

Parasites of managed bees can disrupt the colony success of the host, but also influence local bee-parasite dynamics, which is regarded as a threat for wild bees. Therapeutic measures have been suggested to improve the health of managed bees, for instance, exploiting the bees' RNA interference (RNAi) pathway to treat against viral pathogens. Gut trypanosomes are an important group of bee parasites in at least two common managed bee species, i.e., managed Apis mellifera and reared Bombus terrestris. In several trypanosomes, RNAi activity is present, while in other associated genes of RNAi, such as Dicer-like (DCL) and Argonaute (AGO), it is lost. Up to date, the ability to exploit the RNAi of gut trypanosomes of bees has remained unexplored. Here, we screened parasite genomes of two honey bee protozoa (Crithidia mellificae and Lotmaria passim) and two bumble bee protozoa (Crithidia bombi and Crithidia expoeki) for the presence of DCL and AGO proteins. For C. mellificae, we constructed a double-stranded RNA (dsRNA) targeting kinetoplastid membrane protein-11 (KMP-11) to test the RNAi potential to kill this parasite. Transfection with KMP-11 dsRNA, but also adding it to the growth medium resulted in small growth reduction of the trypanosome C. mellificae, thereby showing the limited potential to apply dsRNA therapeutics to control trypanosome infection in managed honey bee species. Within bumble bees, there seems to be no application potentials against C. bombi, as we could only retrieve non-functional DCL- and AGO-related genes within the genome of this bumble bee parasite.