PA Bureau of Forestry briefs Lycoming County on spongy moth biology, thresholds and treatment options

Rose Yu, a forest health specialist with the Pennsylvania Bureau of Forestry, told Lycoming County commissioners on April 16 that the invasive spongy moth (formerly called the gypsy moth) can cause large-scale defoliation and tree mortality if high populations persist for multiple years. She outlined the insect's life cycle, how the bureau determines whether suppression is required and the tools and timing most effective for control.

Yu said the spongy moth caterpillar prefers oaks but will feed on many plants once preferred hosts are exhausted and that repeated heavy defoliation over two to three years can kill trees, especially if other stressors such as drought are present. "The females don't fly," Yu said, describing a limit on adult moth dispersal; she added that people unintentionally move egg masses and that young caterpillars can balloon on silken threads and be carried by wind.

The bureau uses two main methods to decide where to intervene: aerial surveys followed by ground…