Candidate chemosensory receptors in the antennae and maxillae of Spodoptera frugiperda (J. E. Smith) larvae

Ya-Lan Sun; Peng-Shuo Jiang; Bing-Xin Dong; Cai-Hong Tian; Jun-Feng Dong

doi:10.3389/fphys.2022.970915

Candidate chemosensory receptors in the antennae and maxillae of Spodoptera frugiperda (J. E. Smith) larvae

Front Physiol. 2022 Sep 15:13:970915. doi: 10.3389/fphys.2022.970915. eCollection 2022.

Authors

Ya-Lan Sun¹, Peng-Shuo Jiang¹, Bing-Xin Dong¹, Cai-Hong Tian², Jun-Feng Dong¹

Affiliations

¹ College of Horticulture and Plant Protection, Henan University of Science and Technology, Luoyang, China.
² Institute of Plant Protection, Henan Academy of Agricultural Sciences, Zhengzhou, China.

Abstract

Although most of the damage caused by lepidopteran insects to plants is caused by the larval stage, chemosensory systems have been investigated much more frequently for lepidopteran adults than for larvae. The fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a polyphagous and worldwide pest. To understand the larval chemosensory system in S. frugiperda, we sequenced and assembled the antennae and maxillae transcriptome of larvae in the sixth instar (larval a-m) using the Illumina platform. A total of 30 putative chemosensory receptor genes were identified, and these receptors included 11 odorant receptors (ORs), 4 gustatory receptors (GRs), and 15 ionotropic receptors/ionotropic glutamate receptors (IRs/iGluRs). Phylogeny tests with the candidate receptors and homologs from other insect species revealed some specific genes, including a fructose receptor, a pheromone receptor, IR co-receptors, CO₂ receptors, and the OR co-receptor. Comparison of the expression of annotated genes between S. frugiperda adults and larvae (larval a-m) using RT-qPCR showed that most of the annotated OR and GR genes were predominantly expressed in the adult stage, but that 2 ORs and 1 GR were highly expressed in both the adult antennae and the larval a-m. Although most of the tested IR/iGluR genes were mainly expressed in adult antennae, transcripts of 3 iGluRs were significantly more abundant in the larval a-m than in the adult antennae of both sexes. Comparison of the expression levels of larval a-m expressed chemosensory receptors among the first, fourth, and sixth instars revealed that the expression of some of the genes varied significantly among different larval stages. These results increase our understanding of the chemosensory systems of S. frugiperda larvae and provide a basis for future functional studies aimed at the development of novel strategies to manage this pest.

Keywords: Spodoptera frugiperda; gustatory receptor; ionotropic receptor; larval transcriptome; odorant receptor; real-time quantitative-PCR.