ABSTRACTNosema ceranaeis a new and emerging microsporidian parasite of European honey bees,Apis mellifera, that has been implicated in colony losses worldwide. RNA interference (RNAi), a posttranscriptional gene silencing mechanism, has emerged as a potent and specific strategy for controlling infections of parasites and pathogens in honey bees. While previous studies have focused on the silencing of parasite/pathogen virulence factors, we explore here the possibility of silencing a host factor as a mechanism for reducing parasite load. Specifically, we used an RNAi strategy to reduce the expression of a honey bee gene,naked cuticle(nkd), which is a negative regulator of host immune function. Our studies found thatnkdmRNA levels in adult bees were upregulated byN. ceranaeinfection (and thus, the parasite may use this mechanism to suppress host immune function) and that ingestion of double-stranded RNA (dsRNA) specific tonkdefficiently silenced its expression. Furthermore, we found that RNAi-mediated knockdown ofnkdtranscripts inNosema-infected bees resulted in upregulation of the expression of several immune genes (Abaecin,Apidaecin,Defensin-1, andPGRP-S2), reduction ofNosemaspore loads, and extension of honey bee life span. The results of our studies clearly indicate that silencing the hostnkdgene can activate honey bee immune responses, suppress the reproduction ofN. ceranae, and improve the overall health of honey bees. This study represents a novel host-derived therapeutic for honey bee disease treatment that merits further exploration.IMPORTANCEGiven the critical role of honey bees in the pollination of agricultural crops, it is urgent to develop strategies to prevent the colony decline induced by the infection of parasites/pathogens. Targeting parasites and pathogens directly by RNAi has been proven to be useful for controlling infections in honey bees, but little is known about the disease impacts of RNAi silencing of host factors. Here, we demonstrate that knocking down the honey bee immune repressor-encodingnkdgene can suppress the reproduction ofN. ceranaeand improve the overall health of honey bees, which highlights the potential role of host-derived and RNAi-based therapeutics in controlling the infections in honey bees. The information obtained from this study will have positive implications for honey bee disease management practices.
Physiological effects of the interaction between Nosema ceranae and sequential and overlapping exposure to glyphosate and difenoconazole in the honey bee Apis mellifera
