The mountain pine beetle (MPB, Dendroctonus ponderosae Hopkins) attacks living Pinus trees, and reproduces in the phloem. Adults must attack a host simultaneously to overwhelm host defenses and successfully colonize. Temperatures directly but non-linearly affect MPB progress through life stages and the phenology of adult emergence. MPB are successful in a thermal niche where they are univoltine and synchronize emergence. Changing temperatures have broadened that niche geographically, leading to tree mortality of over 5.2 Mha in the western US.
Successful bivoltine MPB have not been observed in the field, although a phenology model parameterized for northern US MPB populations suggests bivoltinism is possible in the southern MPB range under future warming scenarios. Bivoltinism could have devastating impacts on pine forests. However, northern and southern MPB are genetically different in response to temperature, requiring geographic-specific model parameters. Using rate curves parameterized with developmental observations from MPB in Arizona we have constructed a predictive cohort model for a southern MPB population. Initiating the model with field attack data and using temperature data recorded under the bark of attacked hosts, we simulated warming scenarios by adding to the yearly mean to test thermal regimes that would result in a bivoltine MPB population.
Results/Conclusions
We successfully constructed a predictive cohort model for a southern MPB population. A key result is a new method for projecting observed variability in oviposition, through multiple larval instars, into emergence distributions. Comparison of the cohort model with field emergence data allows us to infer developmental rates for unwitnessed pre-ovipositional adults and also validate model predictions. Model responses to simulated temperatures highlight thermal regimes that promote bivoltinism for the southern MPB population.