Aethina tumida is a parasite and predator of honeybee causing severe loss to the bee industry. No effective and environmentally friendly methods are available to control this pest at present. Chemosensory genes play key roles in insect behavior which can potentially be used as targets for developing environmentally friendly pest control agents. In this study, the putative chemosensory genes in antennae and forelegs of A. tumida involved in olfaction or contact chemical communication of adults were investigated using RNA transcriptome sequencing and PCR methods. Based on transcriptomic data, unigenes encoding 38 odorant receptors (ORs), 24 ionotropic receptors (IRs), 14 gustatory receptors (GRs), 3 sensory neuron membrane proteins (SNMPs), 29 odorant binding proteins (OBPs), and 22 chemosensory proteins (CSPs) were identified. The analyses of tissue expression profiles revealed that genes encoding 38 ORs, 13 antennal IRs, 11 GRs, 1 SNMP, 24 OBPs, and 12 CSPs were predominately expressed in antennae. No significant differences in expression levels of these genes were found between males and females. Genes encoding 5 non-NMDA iGluRs, 3 GRs, 2 SNMPs, 5 OBPs, and 12 CSPs were predominately expressed in forelegs. RT-PCR assays for SNMPs, OBPs and CSPs further revealed that 3 OBPs (AtumOBP3, 26 and 28) and 3 CSPs (AtumCSP7, 8 and 21) were highly expressed in antennae. Our results enrich the gene inventory of A. tumida and facilitate the discovery of potential novel targets for developing new pest control measures.

Varroa destructor is by far the most serious threat to the western honey bee, Apis mellifera. A screen bottom board, a cultural method for mite control, is a modified bottom board with a screen that allows mites to fall onto a sticky board, or the grass or soil below the screen. Whether or not a screen bottom board can reduce varroa significantly has been controversial. Most studies show a trend of lower varroa populations in colonies with these boards, but the results are usually not statistically significant. To understand whether the negative results have been due to small sample sizes, or because the board is actually ineffective, we conducted a meta-analysis with seven published studies with a total of 145 colonies. Meta-analysis showed that the confidence intervals of the combined effect sizes were negative with a Hedges’ g of −1.09 (SE 0.39, 95% CI −2.0 to −0.19, p < 0.01), which suggests that the varroa population in colonies with screen bottom boards is significantly lower compared to those with traditional wooden floors. We thus conclude that the screen bottom board does have a significantly negative impact on the varroa population and can be part of tool kits for mite control.

Background: Odorant binding proteins (OBPs) initiate the process of odorant perception. Numerous investigations have demonstrated that OBPs bind a broad variety of chemicals and are more likely to carry pheromones or odor molecules with high binding affinities. However, few studies have investigated its effects on insect behavior. Previously, we found that AmelOBP4 has a significantly higher expression in the heads of foragers than that of nurses regardless of their ages, revealing its importance in foraging behaviour of the honey bee. RNA interference (RNAi) is the induction of sequence specific gene silencing by double-stranded RNA (dsRNA), it is a powerful tool that makes gene inactivation possible in organisms that were not amenable to genetic analysis before. Results: In this study, we found that AmelOBP4 had high expression levels in the antennae of both nurses and foragers, and could be successfully inhibited by feeding double stranded RNA of AmelOBP4 (dsAmelOBP4). Foragers with inhibited AmelOBP4 showed significantly lower sugar responsiveness than control bees, and also significantly reduced EAG response to plant volatiles of nonanal, linalool and 1-Octen-3ol. On the other hand, nurses with inhibited AmelOBP4 showed significantly reduced EAG response to brood pheromone of ethyl oleate, methyl linoleate, methyl palmitate and β-ocimene. Finally, the Y-tube choice assay showed nurses only exhibited a significantly reduced preference to ethyl oleate, but foragers exhibited significantly reduced preference to all these three plant volatiles. Conclusions: The findings of our study suggested that AmelOBP4 plays an important role in the odorant binding process, especially in modulating olfactory behaviour in workers. Our results provide a foundation for exploring the olfactory mechanism of Apis mellifera.