The summer of 1991 has been a quiet one in California's battle against the Mediterranean fruit fly, but an analysis of historical data by a UC Davis entomologist indicates the destructive agricultural pest isentrenched in the Los Angeles Basin. "The evidence suggests that the medfly is established in the Los Angeles area and that previous programs aimed at eradicating the medfly from California were not successful," says James R. Carey, professor of entomology and a member of the medfly scientific advisory panel for the California Department of Food and Agriculture. "Determining whether the medfly is established or is being reintroduced to the state is important because this in turn dictates the methods we use to detect, exclude and perhaps eradicate the medfly." In 1990, the state of California spent more than $50 million to eliminate the medfly. In a recent issue of the weekly scientific journal Science, Carey applied principles of invasion biology -- the study of how a species becomes introduced and established in a foreign community. Carey cited several basic patterns that support his theory that the medfly is an established species: the few interceptions of medflies at border stations, airports and in the mail; the capture of medflies in the warmer months of summer and fall; and the eastward expansion of the medfly finds from a centralized location. He suggests that the discovery of only one medfly this year may be due to an extremely cold winter. Carey's analysis was published in the Sept. 20 issue of the journal Science.