Dispersal capacity of European gypsy moth (Lymantria dispar dispar) larvae from host vegetation to hardwood log piles

The European gypsy moth (Lymantria dispar dispar) is an invasive forest defoliator of over 300 tree and shrub species. Its range has expanded throughout the northeastern region of the United States and eastern Canadian provinces to Midwestern and Southeastern states primarily through anthropogenic movement. Egg masses, in particular, are readily transported on forest products. To mitigate this spread, state and federal quarantine policies restrict movement of regulated articles such as logs and firewood. Mitigation measures for logs leaving quarantine area include a 100-foot host vegetation-free buffer zone surrounding log decks (i.e., piles of logs stored for future transportation and/or processing) to prevent infestation of logs and adjacent forest by crawling gypsy moth larvae. However, no studies exist which evaluate the long distance dispersal of late instar gypsy moth larvae, the developmental stage with the greatest potential for telluric movement. The location of pupation strongly influences the site of oviposition of the flightless female gypsy moth; therefore, movement of late instar larvae may reduce the effectiveness of containment policies. We released fourth, fifth, and sixth instar gypsy moth larvae daily for six days at a paper mill lumber yard and visually assessed their dispersal over 12 hours with harmonic radar supplementation. Movement of 20 percent of the larvae surpassed the buffer zone width, and the greatest distance achieved was 143.70 feet (43.8 m). These results demonstrate a need to evaluate the forest products movement restrictions related to the gypsy moth quarantine as well as the effectiveness of alternative containment measures.