Geographical origin of an introduced pest species, Delia radicum (Diptera : Anthomyiidae), determined by RAPD analysis and egg micromorphology

The origin of introduction of the cabbage root fly, Delia radicum Linnaeus to the north-eastern coast of North America in the 19th century has been as sumed to be from Europe. From that point of introduction, D. radicum gradua lly spread westward to occupy available ecological niches. DNA fingerprinti ng and egg micromorphology were used to determine the most likely geographi cal origin of the North American populations of this species. Forty-five in formative RAPD loci obtained from ten primers and three criteria for egg mi cromorphology were studied. These characters indicated a common origin for the North American populations and a high similarity between populations fr om North America and north-western Europe. The results suggest a single ent rance point of D. radicum into North America, probably via the north-easter n coast (New York area) from north-western Europe. The implications of this study in assisting selection of natural enemies of this important agricult ural pest are discussed.