Barry County conservation officials report high viral infection among spongy moths and recommend targeted monitoring over broad aerial spraying

Barry County — Barry Conservation District Executive Director Daniel Zollner, district forester Ben Savoy and researcher Dr. Greg Dwyer of the University of Chicago presented the results of a late‑fall spongy moth (Lymantria dispar) egg‑mass survey and related lab testing to the Barry County Board of Commissioners on Jan. 28, 2025.

The Conservation District surveyed plots in five townships and counted egg masses and their viability; lab tests by Dr. Dwyer’s team measured how many caterpillars carry a baculovirus that kills the insects. The presenters said the combination of many nonviable egg masses and very high viral infection in sampled caterpillars indicates the local outbreak is near its peak and likely to decline without broad aerial treatment.

Why this matters: spongy moth caterpillars preferentially feed on oaks and can cause widespread defoliation of forested land. Aerial treatment can be expensive and raises concerns about non‑target species and neighboring property consent. The board was given cost and logistics context, including a local township example that treated roughly 3,000 acres at an approximate cost of $200,000.

The study: Savoy described the field sampling and counts. The district surveyed 31 privately owned sites covering just over 3,000 acres using 1/40‑acre plots centered on host trees. "We sent a survey form out to 207 sites, and we got a response from 43 of them," Savoy said during the presentation. He reported that 84% of egg masses found in the sample were nonviable and that the average egg‑mass density was skewed by a few very high sites, producing a countywide average near 1,168 egg masses per acre.

Dr. Greg Dwyer summarized lab results showing very high fractions of sampled caterpillars dying from a naturally occurring baculovirus. "The virus is basically everywhere and it kills the spongy moths," Dwyer said. He explained the lab protocol and modeling plan: measure the fraction of caterpillars infected when they hatch, then use a population model to predict end‑of‑season caterpillar densities and the likely risk of defoliation.

Recommendations and timing: presenters recommended continued monitoring and a focused approach rather than immediate, countywide aerial spraying. Ben Savoy said decision timing is critical: "March... my best guess, because the insects aren't quite ready to hatch," he said when asked when the county should decide whether to spray. If a spraying decision is made, Savoy estimated the likely aerial application window would be early May, when caterpillars are actively feeding on new leaves.

Risks and logistics: speakers cautioned about costs, drift, and effects on non‑target species such as monarch caterpillars. The typical product for broadcast treatment is Bacillus thuringiensis kurstaki (Btk), which is effective against caterpillars but can overlap with other spring hatching species. Presenters also noted legal and consent complications where neighboring property owners disagree about spraying.

Next steps: the Conservation District will continue sampling in early spring, provide updated model projections to the board and county staff, and assist with public outreach on homeowner control options (egg‑mass scraping, burlap bands, limited homeowner sprays). Presenters encouraged targeted treatments focused on localized hotspots if required rather than a large broadcast program.

Ending: Commissioners thanked the presenters for the detailed field and lab work and endorsed the district’s plan to continue monitoring and public education before committing county resources to a large aerial treatment.