Developing biological control of Alliaria petiolata (M. Bieb.) Cavara and Grande (garlic mustard)

Invasive nonindigenous plants are a primary threat to native species and th e integrity of natural areas by causing changes in species composition and ecosystem processes. For many of the most invasive species, natural area ma nagers lack species-specific and successful long-term management options. M oreover, repeated use of fire, herbicides, flooding, mowing, and other mana gement options may have negative impacts on native species. Increasingly, l and managers are considering biological weed control-the introduction of ho st-specific natural enemies from the native range of a nonindigenous plant species. The spread of garlic mustard (Alliaria petiolata [M. Bieb.] Cavara and Grande), a European biennial herb, through forests of the eastern and midwestern United States and Canada has caused great concern. In 1998 a bio logical control program for garlic mustard was initiated and the search for potential biological control agents began in western Europe. Garlic mustar d is under little herbivore pressure in North America, whereas 70 insect he rbivores and 7 fungi are associated with this plant in Europe. While most o f these species are not sufficiently host-specific to be considered for int roduction into North America, five monophagous weevils and an oligophagous flea beetle that attack seeds, stems, and roots of garlic mustard were sele cted for further study, based on the assumption that simultaneous attack of different plant parts will provide superior control. Although literature r ecords and preliminary investigations suggest that these herbivores have a very restricted host range, extensive experimental investigations will asse ss whether these insects are safe for introduction to North America. Develo pment of successful biological control for garlic mustard will allow natura l area managers to incorporate release of host-specific herbivores into the ir management strategy.