Identification of candidate leg chemosensory genes associated with nursing behavior in the Apis mellifera

It is commonly recognized that legs play a vital role in the chemoreception of insects. The chemosensilla distributed on the legs of the worker bee Apis mellifera are involved in olfactory and gustatory detection. The responses of worker bees of different ages to various compounds were detected using an electrolegogram test on the legs. It was found that a high concentration of the larval starvation pheromone ocimene could trigger electrophysiological responses in 10-day-old worker bees (nurses). Through RNA transcriptome sequencing, the chemosensory proteins in the forelegs, middle legs, and hind legs of nurse bees that may be involved in adult close or contact chemical communication were studied. A total of 56 candidate chemosensory-related proteins, including 17 odorant-binding proteins (OBPs), 5 chemosensory proteins (CSPs), 6 gustatory receptors (GRs), 3 ionotropic receptors (IRs), 2 sensory neuron membrane proteins (SNMPs), and 23 odorant receptors (ORs), were identified from the assembled leg transcriptome. In general, the genes coding for OBPs and CSPs had significant but highly fluctuating TPM values, indicating high-level expression in the legs of nurses. In contrast, the chemosensory receptors ORs, GRs, and IRs showed low-level expression. In particular, AmelOBP21, AmelCSP3, AmelOR170, AmelGR3, AmelIR21, and AmelSNMP1, which were relatively highly expressed, may play olfactory and gustatory functions in the process of nurse bees recognizing larval starvation signals and initiating nursing behaviors. These results lay a foundation for further research on the chemoreception of legs in the honey bee A. mellifera.