CRISPR/Cas9 in locusts: Successful establishment of an olfactory deficiency line by targeting the mutagenesis of an odorant receptor co-receptor (Orco).

Locusts are important agricultural pests worldwide and regarded as study models for entomology. However, the absence of targeted gene manipulation systems for locusts has restricted their applications for research. Herein, we report the successful use of the CRISPR/Cas9 system to induce a targeted heritable mutagenesis of the migratory locust, Locusta migratoria. The target sequence of gRNA was designed to disrupt the gene encoding the odorant receptor co-receptor (Orco) and examine the roles of the odorant receptor pathway in the locust. Microinjection of the mixture of Cas9-mRNA and Orco-gRNA into the locust eggs resulted in efficient target-gene editing at a rate of 71.7% in G0 animals and achieved a germline efficiency of up to 88.1% in G1 animals. By a crossing strategy, we successfully established stable Orco mutant lines. EAGs and SSRs indicated that the fourth-instar nymphs of the Orco mutants showed severely impaired electrophysiological responses to multiple odors. The Orco mutant locusts lost an attraction response to aggregation pheromones under the crowding conditions. The locomotor activity and body coloration of the Orco mutant locusts did not significantly differ from those of the two other genotypes. This study provides an easy and effective approach by using the CRISPR/Cas9 system for generating loss-of-function mutants for functional genetic studies of locusts and for managing insect pests.