Precise maps of invasive insect impacts aid detection and monitoring

Precise mapping of invasive spongy moth defoliation yields rich insight into the vulnerability of eastern forests and the effectiveness of costly treatments.

A map demonstrates spongy moth defoliation: a line of severe defoliation stretches across horizontally, with light defoliation spreading out from there. On the middle-left of the map there is a clear area with no defoliation, due to spraying. — Spongy moth defoliation is shown by this 2-year change in vegetation for a portion of Lycoming County, PA, during early summer in 2022. Blue shows normal canopy conditions outside the outbreak zone or from spraying efforts to control defoliation. Yellow shows light defoliation and orange, red and purple show severe foliage loss. Map by Steve Norman, USDA Forest Service.

Nonnative invasive insects have beleaguered eastern forests for decades, and the spongy moth (Lymantria dispar dispar) has been one of the most troublesome. For half a century, the standard approach to mapping spongy moth defoliation was through costly aerial surveys. In recent years, a collaboration between USDA Forest Service scientists and federal and state agencies has demonstrated the value of remote sensing imagery. In 2021 and 2022, researchers mapped spongy moth defoliation at 10-meter resolution across several states.

In Pennsylvania, these maps showed where defoliation had not occurred within large defoliation zones, and this showed the effectiveness of costly insecticide spraying programs on state lands. While spraying is not formally reported for private lands, the maps also revealed where some unreported spraying occurred. In addition, detailed maps can show state agencies where defoliation occurred and its severity to anticipate where to conduct winter egg mass surveys and where to spray next spring more efficiently. Improved documentation of repeated defoliations can inform cumulative impacts and tree mortality.

Additional links

Principal Investigators: Steve Norman, Research Ecologist; Bill Christie, Biological Scientist; William Hargrove, Research Ecologist
RWU: 4854 - Eastern Forest Environmental Threat Assessment Center
Publication: Precise mapping of disturbance impacts to U.S. forests using high-resolution satellite imagery
Research Partner: Stephen Burr, State and Private Forestry
External Partners: Don Eggen, Pennsylvania Bureau of Forestry; Sarah Johnson, Pennsylvania Bureau of Forestry