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INVESTIGATOR: Mihaljevic, J.

PERFORMING INSTITUTION:
UNIVERSITY OF CHICAGO
5801 SOUTH ELLIS AVE.
CHICAGO, ILLINOIS 60637

USING EPIDEMIOLOGICAL MODELING TO IMPROVE MICROBIAL CONTROL OF THE DOUGLAS-FIR TUSSOCK MOTH

NON-TECHNICAL SUMMARY: The Douglas-fir tussock moth (DFTM), Orgyia pseudotsugata, causes severe defoliation and economic loss to multiple fir species across western North America during cyclical outbreaks. These outbreaks are typically terminated by epizootics of the naturally circulating baculovirus, OpNPV. Due to the host-specificity and high virulence of OpNPV, the USDA Forest Service uses the virus as a microbial pesticide, TM Biocontrol-1 (TMB). Recent field trials with TMB have shown that, although spraying TMB sometimes leads to reductions in defoliation, overall larval mortality rates often do not differ from unsprayed, control plots that become infected with naturally circulating OpNPV. This result is perplexing because in plots infested by naturally circulating OpNPV, initial infection rates are much lower than in TMB-sprayed plots.As my primary objective, and in the hopes of improving future management efforts, I will use epidemiological modeling, complemented by field and laboratory experiments, to determine if there are ecological differences between TMB and naturally circulating OpNPV strains that could account for previous management outcomes. As a secondary, broader project objective, I will seek to understand how future climate warming may influence the efficacy of TMB compared to naturally circulating OpNPV strains. I will conduct laboratory experiments to determine how TMB and two wild-type strains of OpNPV perform at different temperatures. I will then use my models to make predictions about how a changing climate may affect epizootic dynamics and microbial control in the DFTM system.

OBJECTIVES: The Douglas-fir tussock moth (DFTM), Orgyia pseudotsugata, causes severe defoliation and economic loss to multiple fir species across western North America during cyclical outbreaks. These outbreaks are typically terminated by epizootics of the naturally circulating baculovirus, OpNPV. Due to the host-specificity and high virulence of OpNPV, the USDA Forest Service uses the virus as a microbial pesticide, TM Biocontrol-1 (TMB). Recent field trials with TMB have shown that, although spraying TMB sometimes leads to reductions in defoliation, overall larval mortality rates often do not differ from unsprayed, control plots that become infected with naturally circulating OpNPV. This result is perplexing because in plots infested by naturally circulating OpNPV, initial infection rates are much lower than in TMB-sprayed plots. The over-arching goal of this project is to use rigorous quantitative methods to differentiate between mechanisms that could cause these surprising management results.Objective 1: As my primary objective, and in the hopes of improving future management efforts, I will use epidemiological modeling, complemented by field and laboratory experiments, to determine if there are ecological differences between TMB and naturally circulating OpNPV strains that could account for previous management outcomes.Objective 2: As a secondary, broader project objective, I will seek to understand how future climate warming may influence the efficacy of TMB compared to naturally circulating OpNPV strains. I will conduct laboratory experiments to determine how TMB and two wild-type strains of OpNPV perform at different temperatures. I will then use my models to make predictions about how a changing climate may affect epizootic dynamics and microbial control in the DFTM system.