State reports continued winter moth defoliation in coastal Maine and ongoing parasitoid releases

Alison (presenter) summarized winter moth ecology and recent field observations across Maine’s mid‑coast and peninsulas, noting that caterpillars hatch in early spring (March–April), feed from buds and young leaves, and can cause multi‑year defoliation that contributes to hardwood decline when combined with drought and other stressors.

She described the specialist parasitoid fly Calesinus albocans (a tachinid‑type parasitoid) as the primary biological control used in Maine. Releases began in 2013 and have continued where rearing yields permit; flies are reared from wild‑collected caterpillars in university labs and then caged for winter burial until spring emergence.

Alison said multi‑jurisdictional collections in recent seasons produced more than 11,000 collected caterpillars, from which roughly 800 fly pupae were available for overwintering in cages this year—an outcome she described as helpful but still limited relative to need. She emphasized that the parasitoid program is slow to spread across peninsulas and will take many years to reduce outbreak intensity in some localities.

Management options described included dormant‑oil sprays to suffocate eggs, sticky banding to intercept crawling females, Bt (Bacillus thuringiensis var. kurstaki) for young caterpillars shortly after leaf‑out, and targeted conventional insecticides or trunk injections when caterpillars are larger. She cautioned against moving soil or plant material from infested areas because winter moth pupae in soil can spread the pest.

The presenter closed by noting the state continues to seek federal and regional support for a coordinated biological‑control program and asked communities to report infestations to help prioritize collection and release sites.