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    We conducted an experimental study of infection, transmission, and persistence of a nucleopolyhedrovirus (NPV) of Douglas-fir tussock moth (Orgyia pseudotsugata) to better understand mechanisms determining the efficacy of the virus when it is used as a microbial control agent. In a field experiment, we quantified infection rates of larvae exposed to either Tussock Moth Biocontrol-1, the strain currently used for control by the U.S. Forest Service, or a wild-type strain isolated from a natural population. We first allowed each pathogen to decay on experimental branches for 0, 1, or 3 days before allowing uninfected larvae to feed on the branches, and then we fit both a generalized linear model and an epidemiological model of virus transmission to the infection data. Longer decay of the NPV resulted in lower infection rates, but evidence that overall virus transmission differed between wild and pesticide isolates of NPV was weak. The short persistence time of the virus suggests that it does not last long on foliage, in turn suggesting that application of TM Biocontrol-1 must be carefully timed to ensure maximum mortality.

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    Polivka, Karl M.; Dwyer, Greg; Mehmel, Constance J. 2017. Environmental persistence of a pathogen used in microbial insect control. Res. Note. PNW-RN-573. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 15 p.


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    Douglas-fir tussock moth, baculovirus, biocontrol, epidemiological model.

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