Eradication is possible: the gypsy moth success story in Oregon

In 1984, 19,019 gypsy moths, Lymantria dispar (L.), were found over 1,200 mi² in Lane Co., Oregon - the largest gypsy moth infestation ever found in the western U.S. In 1985, a large-scale eradication program consisting of quarantines, applications of Bacillus thuringiensis var. kurstaki, posttreatment mass-trapping (3-9 traps/acre in core areas) and delimitation surveys (16 traps/ mi²) within the 1,200 mi² quarantine area was initiated. The number of moths trapped and acres treated declined in each of four successive years: 1985 - 226,405 acres treated, 1,278 moths trapped; 1986 - 189,011 acres treated, 81 moths trapped; 1987 - 7,135 acres treated, 41 moths trapped; 1988 - 2,995 acres treated, 1 moth trapped. In 1989, the quarantine was lifted after two moths were trapped and determined to be recent introductions and not evidence of an incipient population. Since 1984, numerous smaller gypsy moth eradication programs have also been conducted in Oregon. All have been considered successful after two successive years of negative posttreatment surveys of 16-49 traps/ mi². Contributing to this success are an effective pheromone capable of detecting populations at low levels, annual statewide surveys conducted on a rotating grid basis, and flightless females (North American strain) resulting in relatively limited natural spread. In many cases the source, means, and time of introduction from an infested state are found within one to two years of an initial trap detection indicating these are new introductions and not an incipient population that may take several years to reach detectable levels.