Molecular and functional analysis of chitin synthase genes in Chilo suppressalis (Lepidoptera: Crambidae)

The rice stem borer, Chilo suppressalis, has developed a high level of resistance to many of the compounds currently used for control. There is therefore an urgent need to develop novel control methods for C. suppressalis. Insect chitin synthases (CHS) have attracted interest as a potential target for insect pest management. However, to date, CHS have not been characterized in C. suppressalis. Two CHS genes (CsCHS1 and CsCHS2) were identified and cloned from C. suppressalis. Two transcript variants were identified for CsCHS1, CsCHS1a and CsCHS1b. Spatiotemporal expression profiling showed that both transcripts of CsCHS1 are most highly expressed on the last day of each larval instar stage and show the highest expression levels in the integument. In contrast, CsCHS2 is predominantly expressed during the larval feeding stages and shows the highest expression levels in the midgut. Knockdown of CsCHS1 by RNA interference significantly inhibited the molting and pupation of C. suppressalis, and knockdown of CsCHS2 significantly affected growth during the larval stage, but had no significant effect on the pupation. Moreover, knockout of CsCHS1 by CRISPR/Cas9 genome editing severely lowered the hatching rate, larval survivorship, pupation rate, and eclosion rate, but only larval survivorship at the G0 generation was lowered after the knockout of CsCHS2. These results demonstrate that CsCHS1 and CsCHS2 play vital roles in the growth and development of C. suppressalis, and so have potential as insecticidal targets for the control of this highly damaging pest.