Biological control is an important and sustainable approach for managing widespread invasive weeds. In biological control, host specific natural enemies (usually insects) are introduced with the goal of establishing a permanent population that will provide sustained, cost-effective control of the plant. The overall goal of this project is to preserve and enhance the effectiveness of biological control for weeds on Department of Defense (DoD) installations, by understanding of the phenological constraints that may arise with a change in climate as a result of the insects’ combined responses to photoperiod and temperature, and the follow-on impacts to the plant populations. This work applies to three important weed species that are currently (or soon to be) targets for biological control: purple loosestrife, tamarisk, and Japanese knotweed.

Researchers will first expand and improve the existing geo-climatic phenology model, which provides an innovative approach to tracking life cycle responses to both temperature and photoperiod. The model will be used to predict phenology, voltinism (number of generations per year), and the degree of asynchrony between the biocontrol agent’s life cycle and the host plant’s growing season under new climate conditions. A series of laboratory and field experiments will be carried out to test model predictions. Controlled environment chambers will be used to quantify and compare the photoperiod response among populations and to obtain parameter estimates for the model. Time-lapse field cameras and temperature data loggers will monitor plant phenology and insect voltinism. Reciprocal transplant experiments will be used to (1) test model predictions about phenological response to a change in climate, (2) confirm that the observed changes in photoperiod response represent local adaptation, and (3) quantify the follow-on impacts of these phenological shifts for the host plant. Once validated, researchers will apply the model and experimental outcomes to design strategies for improving biological control for the three target weeds and develop climate change prospectus reports for each weed system at each of six or more DoD installations. Finally, researchers will share the model framework and encourage its application for other species of concern on DoD lands, including other biocontrol agents, invasive forest pests, an threatened and endangered species. The model itself will be made publically available online as part of an advanced degree-day phenology modeling system developed and managed by the Integrative Plant Protection Center at Oregon State University.

This research will have immediate and direct benefits for improving the effectiveness of weed biological control programs, including current and future programs, by providing better predictability of the phenological consequences of exposing insect biocontrol agents to new climates. The results will greatly contribute to the general theoretical understanding of the complex interactions of photoperiodism and thermal responses under climate change. This innovative model will be placed online where it can be accessed by other scientists and applied to other biocontrol systems and other organisms of management concern.