An infestation of the New World Screwworm fly has spread across livestock in Mexico in the past year, prompting binational efforts to slow the parasite. (Courtesy of U.S. Department of Agriculture)New Mexico state and federal officials this week expressed concern about the encroachment of a parasitic fly into the state even as federal officials in March unveiled a flurry of efforts to combat the insect’s spread. The New World screwworm, aptly na…