United States Department of Agriculture-Animal and Plant Health Inspection Service
Plant Protection and Quarantine-Center for Plant Health Science and Technology

Pathways of entry into the United States obviously change with time and with technological advances. Sailer (1978) believes that some of our immigrant insects can be traced to the Mayflower's arrival at Plymouth Rock in 1620. Particularly those insects living in stored products or as human ectoparasites were able to survive long sea voyages. Thus, the bed bug (Cimex lectularius) and cockroaches were among the first pests to be introduced, although no published records document this supposition (Sasser 1940). Another pest well established in colonial times was the mosquito Aedes aegypti, which apparently was introduced with drinking water casks (G.G. Craig,). The transport of
domestic animals also resulted in the establishment of ectoparasitic species and a few that develop in manure. Ship's ballast was a principal early source of immigrant insects including many of our adventive ground-dwelling beetles (Carabidae, Staphylinidae). Several sawfly species that pupate in the soil probably also were introduced in ballast (Benson 1962).

Importation of plants or parts of plants for propagation has been a particularly important pathway of introduction (e.g., Howard 1898; Adamson 1941; Swain 1952; Sailer 1978, 1983). Insects were introduced on plants as well as in soil, packing material such as straw, or wood cases used for transporting plants (Howard 1895). During the eighteenth century, such important plant pests as the Angoumois grain moth (Sitotroga cerealella), codling moth (Cydia pomonella), Hessian fly (Mayetiola destructor), pear sawfly (Caliroa cerasi), and oystershell scale (Lepidosaphes ulmi) were introduced (Sasscer 1940).

Development of the Wardian case in 1834, essentially a miniature air-sealed greenhouse, facilitated the movement of plants in a growing (rather than dormant) state. Plants then could better survive the long sea voyage from Europe, which increased the risks of pest introduction.  A great demand for imported ornamental plants, especially after the Civil War, led to an almost limitless flow of European nursery stock (Wheeler and Henry 1992 and references therein). Millions of living plants entered each year until quarantine laws began to restrict the free movement of plants. The shipment of European plant material resulted in the establishment of cryptic pests such as scale insects, species that breed in seeds or parasitize plant feeders, and leafhoppers, plant bugs, and other groups that insert their eggs into plant tissues.

(All text on this page is from Kim & Wheeler's 1991 report.)