Distribution of an exotic pest, Agromyza frontella (Diptera: Agromyzidae), in Manitoba, Canada

Agromyza frontella is an exotic alfalfa pest from Europe that was first detected in North America in 1968 and has since spread westward into Ontario and the north central United States. Informal surveys had detected A. frontella in Manitoba, but its distribution throughout this province was unknown. In 1998 we collected alfalfa stems to detect plant damage and sweep samples to detect adult A. frontella and the parasitoid Dacnusa dryas throughout the alfalfa growing region of Manitoba. In south central Manitoba, 100% of stems were damaged by A. frontella, and > 100 adults/10 sweeps were recorded at several sites. In west central Manitoba, no plants were damaged and < 10 adults/10 sweeps were observed. We believe this region to be near the western edge of A. frontella distribution. The most important introduced parasitoid of A. frontella, D. dryas, was not detected which suggests that D. dryas has not invaded Manitoba.