Spinosad-associated modulation of select cytochrome P450s and glutathione S-transferases in the Colorado potato beetle, Leptinotarsa decemlineata.

The Colorado potato beetle (Leptinotarsa decemlineata (Say)) is an insect pest that threatens potato crops. Multiple options exist to limit the impact of this pest even though insecticides remain a primary option for its control. Insecticide resistance has been reported in Colorado potato beetles and a better understanding of the molecular players underlying such process is of utmost importance to optimize the tools used to mitigate the impact of this insect. Resistance against the insecticide spinosad has been reported in this insect and this work thus aims at exploring the expression of targets previously associated with insecticide response in Colorado potato beetles exposed to this compound. Amplification and quantification of transcripts coding for cytochrome P450s and glutathione S-transferases were conducted via qRT-PCR in insects treated with varying doses of spinosad and for different time duration. This approach notably revealed differential expression of CYP6a23 and CYP12a5 in insects exposed to low doses of spinosad for 4 h as well as modulation of CYP6a13, CYP6d4, GST, GST1, and GST1-Like in insects treated with high doses of spinosad for the same duration. RNAi-based targeting of CYP4g15 and CYP6a23 was associated with marked reduction of transcript expression 7 days following dsRNA injection and reduction of the former had a marked impact on insect viability. In general, results presented here provide novel information regarding the expression of transcripts relevant to spinosad response in Colorado potato beetles and reveal a novel target to consider in the development of RNAi-based strategies aimed at this potato pest.

Silencing of Molecular Targets with Relevance to Insecticide Resistance in Colorado Potato Beetle Using dsRNA.

Various approaches based on RNA interference (RNAi) have garnered significant attention in the field of insect pest management in recent years. For example, the use of double-stranded RNA (dsRNA) has notably been investigated to target transcripts of interest with relevance to insecticide resistance in multiple pests and has emerged as a potential tool to be deployed in agricultural fields in the near future. A careful characterization of a given dsRNA in a laboratory setting, including the assessment of dsRNA-mediated molecular and phenotypical changes observed in the targeted pest upon dsRNA exposure, is nevertheless essential prior to its use in field-based study. The current chapter thus describes the process via which a dsRNA, aimed at a molecular target underlying insecticide response in the Colorado potato beetle Leptinotarsa decemlineata, is conceived, synthesized and injected. Assessment of knockdown efficiency in injected insects is further presented.