To aid in optimizing control of insect pests of trees, the USA National Phenology Network (USA-NPN) developed models to create maps that predict the emergence of the pests in localities throughout the U.S., such as apple maggot (Rhagoletis pomonella), for which the forecast map from July 1, 2019, is shown here. Explore more Pheno Forecast maps. (Screenshot retrieved from USA National Phenology Network Visualization Tool, February 11, 2020.)

By John P. Roche, Ph.D.

Insect pests cause billions of dollars in damage each year and they spread numerous dangerous diseases. If professionals attempting to control pest insect species had information about when those species reached the developmental stages at which they are most vulnerable to control measures, management efforts could be more economical, more effective, and less damaging to nontarget species and the environment.

To provide such a resource on a nationwide scale, the USA National Phenology Network (USA-NPN) developed its “Pheno Forecast” maps. The program provides daily maps and forecasts for target pest species that forest managers and integrated pest management professionals can use to optimize their pest-control efforts. The program presently focuses on pests of woody species, but plans are in development to expand the program to include other categories of insects.

Theresa Crimmins, Ph.D., is assistant director of USA-NPN, headquartered at the University of Arizona’s School of Natural Resources and the Environment. Crimmins and colleagues at UA, the U.S. Geological Survey, Oregon State University, Cornell University, the Davey Tree Expert Company, and the USDA Forest Service have authored a report that showcases the Pheno Forecast tool and its applications, published today in the Annals of the Entomological Society of America. The report is one of eight new articles published today as part of a new special collection in the journal on geospatial analysis of invasive insects.

The USA National Phenology Network Pheno Forecast maps are one tool showcased in a new special collection on Geospatial Analysis of Invasive Species, published in February 2020 in the Annals of the Entomological Society of America, in partnership with the National Invasive Species Council. Read the collection now.

Because insects depend on external thermal energy for many of their functions, accumulation of heat is a central physical characteristic affecting insects’ progression through their life stages. Pheno Forecasts use heat—measured via temperature—as a way to predict insect developmental events. (Heat is the total kinetic energy of molecules in a material, whereas temperature is the average kinetic energy of molecules.) The USA-NPN phenology maps plot insect development thresholds based on heat accumulation for localities throughout the U.S. For each species, the phenology maps use a specific base temperature value—the temperature below which warmth is not biologically relevant to the species. They then look at heat accumulation in a geographic site relative to that base temperature and report heat accumulation thresholds that correlate with developmental change in the target insect species. The base temperature and heat accumulation thresholds are based on values in the research literature.

Every night, USA-NPN generates a daily map and a six-day forecast for each target pest species. The program posts these maps each night on its website. Maps are color-coded so that users can easily see predicted life cycle stages throughout the country. An example of a Pheno Forecast map for apple maggot on July 1, 2019, is shown at the top of this post.

Phenology forecast maps have been used for years, but, in the past, predictive information was only available for limited locations and regions. The USA-NPN program provides predictive information in a readily accessible format for the entire country. Now users can look up heat accumulation for any specific site at any time.

Design of the program and selection of the target species were developed in consultation with experts from the U.S. Geological Survey (USGS), the U.S. Department of Agriculture, the National Park Service, several universities, and the landscaping and arborist industries. USA-NPN, founded in 2007, is funded primarily through the USGS, while the administration of its National Coordinating Office is led by the University of Arizona. The species for which USA-NPN currently provides Pheno Forecast maps are apple maggot (Rhagoletis pomonella), Asian longhorned beetle (Anoplophora glabripennis), bagworm (Thyridopteryx ephemeraeformis), bronze birch borer (Agrilus anxius), Eastern tent caterpillar (Malacosoma americanum), emerald ash borer (Agrilus planipennis), gypsy moth (Lymantria dispar), hemlock wooly adelgid (Adelges tsugae), lilac borer (Podosesia syringae), magnolia scale (Neolecanium cornuparvum), pine needle scale (Chionaspis pinifoliae), and winter moth (Operophtera brumata) .

The forecasts are disseminated via the USA-NPN webpage, newsletters, and social media. The USA-NPN webpage provides a wealth of information in an easy-to-use interface, and it includes a visualization tool where users can filter data by year or species, select data by geographical location, or compare two sets of data with a scatterplot. Users can sign up to receive location-based alerts when a life cycle stage for a species of interest is predicted to occur within the next two weeks and within the next six days. There were over 18,000 visits to the USA-NPN webpage in 2018.

Founded in 2007, the USA National Phenology Network (USA-NPN) is funded primarily through the U.S. Geological Survey, while the staff team (pictured here) at the USA-NPN National Coordinating Office is headquartered at the University of Arizona’s School of Natural Resources and the Environment. (Photo courtesy of Theresa Crimmins, Ph.D.)

“The most immediate benefit of the Pheno Forecast maps is in helping individuals who manage for these tree pests—tree care specialists, arborists, foresters, and natural resource managers—anticipate when they might want to take action to control the pest,” Crimmins says.

She also notes that the maps are a practical application of years of biological research on insect pest species. “We didn’t develop the predictive models that are used to generate the maps and forecasts; what we did was mine the literature and seek expert input on simple models that seemed to accurately predict the timing of key events in troublesome species,” Crimmins says. “Our constraints are the availability of existing models—or data to build new ones—and data for validation and verification.”

When asked about next steps in the USA-NPN program, Crimmins says, “We have several plans in mind for the Pheno Forecast maps. First, we plan to compare the reports of the species on the ground to our forecasts. Based on these results, we may make changes to the models used to make the forecast maps with the aim of generating more accurate maps in subsequent years.” Such validation will be done by comparing data in the phenology maps with reports of observed insect life cycle events in the field found in Nature’s Notebook, the plant and animal phenology observing program run by the USA-NPN. “Further,” Crimmins says, “we plan to extend our approach to deliver longer-lead-time Pheno Forecasts, predicting insect pest activity weeks to months into the future.”

Crimmins also says that she and her colleagues want to add maps for more species, based on suggestions from users. And they are interested in extending the forecasts to the phenology of native pollinator species, such as butterflies.

While still in its early stages in terms of the number of species covered, the USA-NPN program has immense promise as a tool that can save money, increase pest-management effectiveness, and decrease nontarget environmental impacts. And if some day it can be developed as a resource for predicting emergence of agricultural pests and disease-vectoring mosquitoes, it could become one of the most beneficial resources available to pest-management specialists in the U.S. Because it is designed to be a consultative resource, its content and direction will continue to evolve with the interest of its users. You can learn more and partner with USA-NPN at www.usanpn.org/partner.

John P. Roche, Ph.D., is an author, biologist, and educator dedicated to making rigorous science clear and accessible. Director of Science View Productions and Adjunct Professor at the College of the Holy Cross, Dr. Roche has published over 200 articles and has written and taught extensively about science. For more information, visit https://authorjohnproche.com.