Abstract: 【Aim】 To analyze and elucidate the molecular characteristics and function of the gustatory receptor gene EscrGR8 in Eucryptorrhynchus scrobiculatus, and to reveal its role in the regulation of the fecundity of female adult. 【Methods】 Based on the antennal transcriptome database of E. scrobiculatus, the cDNA full-length sequence of EscrGR8 was cloned using RACE. The expression levels of EscrGR8 in different developmental stages (egg, 1st－6th instar larvae, pupa, female adult, and male adult), and female and male adult tissues (head without antennae and proboscis, antennae, mouthparts, midgut, forefoot, testicles, ovaries, male copulatory organ and female ovipositor) of E. scrobiculatus were detected by qRT-PCR. The expression levels of EscrGR8 at 0, 6, 12, 24, 36, 48 and 72 h after RNAi through microinjection of dsRNA into female adults were detected by qRT-PCR. The oviposition selection rates, total numbers of eggs laid and hatching rates of eggs laid by female adults under different soil moisture conditions (0-10%, 11%-20%, 21%-40%, 41%-60%, 61%-80%, and 81%-100%) at 1-5 d and 6-11 d after dsEscrGR8 microinjection were determined, and the effects of inhibition of the EscrGR8 expression on the oviposition preference and fecundity of female adults were studied. 【Results】 The full-length cDNA sequence of EscrGR8 (GenBank accession no.: OR836580) of E. scrobiculatus was successfully cloned with the open reading frame (ORF) of 1 251 bp in length, encoding 416 amino acids. EscrGR8 has six transmembrane domains. Multiple sequence alignment and phylogenetic analysis results showed that EscrGR8 has a low homology to the GRs of other insects, and the amino acid sequence identity with AgraGR64f of Anthonomus grandis is 30.96%. qRT-PCR result showed that there were significant differences in the expression levels of EscrGR8 in different developmental stages and adult tissues of E. scrobiculatus. EscrGR8 had the highest expression level in female adults, and the lowest expression level in eggs. EscrGR8 was highly expressed specifically in the female ovaries. Microinjection of dsEscrGR8 not only significantly reduced the expression level of EscrGR8 within a certain period of time, but also had a significant impact on the oviposition preference of female adults. At 1-5 d after microinjection of dsEscrGR8, the oviposition selection rate and hatching rate of eggs laid by female adults under soil condition with the moisture content of 21%-40% were significantly reduced by 2466% and 1583%, respectively, compared with those of the dsGFP-microinjected control group. The oviposition selection rate increased significantly by 28.39% under soil condition with the moisture content of 81%-100%, and almost all of the eggs laid by female adults failed to hatch. 【Conclusion】 This study has confirmed the effect of gustatory receptor gene EscrGR8 on the oviposition preference and fecundity of female adults of E. scrobiculatus, which is helpful for understanding the diversity and functional specificity of gustatory receptor genes in insects.

Key words: Eucryptorrhynchus scrobiculatus, egg production, gustatory receptor gene, RNAi, expression pattern