GENE SILENCING PROVIDES INSIGHTS INTO BARK BEETLE BIOLOGY AND CREATES POTENTIAL FOR BROAD SCALE FOREST PROTECTION

Dendroctonus bark beetles are among the most economically and ecologically significant forest pests in North America and play a critical role in the overall health of conifer forest ecosystems. Dendroctonus bark beetles influence ecosystem benefits and biodiversity and drive forest succession, and adversely affect timber production, forest management, and recreation. As temperatures surge and climatic fluctuations become more extreme, catastrophic bark beetle outbreaks are increasing in frequency, escalating pressures on highly vulnerable conifer forests already compromised by heat and drought. Eruptive outbreaks of Dendroctonus beetles are largely unhindered by traditional silvicultural management; these practices further disrupt forest ecosystem services, including the capacity to sequester carbon, thereby compromising their ability to temper our changing climate. The limitations of current management approaches for Dendroctonus beetles makes them prime targets for innovative and aggressive management strategies that are less taxing ecologically. RNA interference is one such innovative approach touted as a next generation pest control tactic. RNA interference (RNAi) is a naturally occurring eukaryotic immune response that can be artificially manipulated through the introduction of carefully designed double stranded RNAs (dsRNAs) to silence gene function. Gene silencing via RNAi is a powerful tool used to elucidate gene function and expose inter-individual epigenetic differences and can also be applied in pest management as a biopesticide. I investigated the use of RNAi technology in Dendroctonus bark beetles. Chapter one offers an overview of Dendroctonus systems. In Chapters Two and Three I demonstrate the efficacy of RNAi to silence gene function in southern and mountain pine beetles, Dendroctonus frontalis and D. ponderosae, respectively. I show that triggering the RNAi pathway in each species halts the production of critical proteins and results in significant mortality in a species-specific manner. I then investigated the specificity of RNAi to target in Chapter Four and found that the technology has congeneric effects. In Chapter Five I demonstrate a marked sensitivity to epigenetic changes spurred by differences in climate and host in southern pine beetle. I then investigated potential deployment methods of RNAi technology for forest-wide southern pine beetle suppression, beginning with the transformation of southern pine beetle associated fungi to act as a delivery mechanism for RNAi inducing dsRNAs in Chapter six, followed by the identification and validation of olfactory receptor genes and the specific pheromones to which they correspond in Chapter Seven. Chapter Eight highlights that, collectively, my work offers new insights into Dendroctonus bark beetle biology and is a foundational step to adapting RNAi technology to broadscale forest protection