Undesirable invasive plants are infesting public and private lands in this country at an alarming rate. These nonnative species destroy native habitats, threaten endangered plants and animals, interfere with recreation and transportation, and cause economic losses as land values and productivity decline. Various methods are used to suppress invasive plants, from herbicides to burning to cultivation. Classic biological control--in which selected host-specific, plant-attacking insects, mites, nematodes, and pathogens are introduced from the invasive plant's native lands--provides an additional...