Abstract
The efficacy and high specificity of the RNA interference pathway has prompted its exploration as a potential molecular management tool for many insect pests, including the destructive southern pine beetle, Dendroctonus frontalis Zimmermann, in which gene knockdown and mortality via double-stranded RNAs (dsRNAs) have already been demonstrated in the laboratory. The nucleotide sequence of dsRNAs requires an exact match of at least 16 nucleotides with the targeted messenger RNA to trigger knockdown of that gene. This allows vital genes in a target pest to be silenced and mortality induced while reducing the probability of adverse effects in nontarget organisms. However, prior to utilization in forest ecosystems, demonstration of the specificity of dsRNAs through laboratory bioassays evaluating potential nontarget effects on model insects is required for proper risk assessment analyses. Consequently, we evaluated three SPB-specific dsRNAs for lethal effects, sublethal effects (larval growth rate, adult emergence or adult fecundity), and relative gene expression in three model nontarget insects representing key functional guilds, including a predator, herbivore, and pollinator. The SPB-specific dsRNAs had no effect on survival of our nontarget insects. Additionally, no sublethal effects were found and the gene expression analyses corroborated bioinformatic analyses in finding no gene knockdown. Our findings support the high specificity of RNAi technology and provide support for its development and deployment for protection of conifer forests against SPB with minimal nontarget concerns.
Highlights
IntroductionBoth economic (Pye et al 2011) and ecological (Tchakerian and Coulson 2011); implementing effective forest management strategies is essential to maintaining their function
Communicated by Guy Smagghe.Forests provide immeasurable benefits, both economic (Pye et al 2011) and ecological (Tchakerian and Coulson 2011); implementing effective forest management strategies is essential to maintaining their function
RNA extracted from southern pine beetle (SPB) adults was used to synthesize complementary DNA which was used in a polymerase chain reaction (PCR) to amplify DNA using the above double-stranded RNAs (dsRNAs) primer sequences
Summary
Both economic (Pye et al 2011) and ecological (Tchakerian and Coulson 2011); implementing effective forest management strategies is essential to maintaining their function. Temperate and boreal forests have experienced unprecedented pressure from bark beetle outbreaks Curculionidae, Scolytinae), reducing their economic value and threatening wildlife habitat, forest biodiversity, and their role in global carbon sequestration. Insecticides, while effective for bark beetle suppression, are impractical on a forest-wide scale (Grosman et al 2009), and traditional bark beetle management has relied on silvicultural techniques to improve tree health and reduce susceptibility (Belanger et al 1993; Nebeker 2004). The current management approaches are proving increasingly inadequate against outbreaking bark beetle populations, prompting investigations into novel mitigation strategies. Gene silencing through manipulation of the cellular RNA interference (RNAi) pathway is one such innovative approach
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