Twenty isolates of the fungus Metarhizium anisopliae (Metsch). Sorkin (Ma) were evaluated to determine their virulence against last instar and adult emergence of Mexican fruit fly, Anastrepha ludens (Loew). Larvae were exposed by immersion in a conidial suspension at a concentration of 10(8) UFC/ml under laboratory conditions. Larvae and pupae cumulative mortality rates ranged from 37.9 to 98.75%. Thirteen isolates caused mortality rates > 83.7%, and their LT50 values ranged from 1.8 to 6.2 d. The Ma2, Ma8, and Ma16 isolates were evaluated at seven different concentrations ranging from 10(1) to 10(7) UFC/ml, showing LC50 values from 3.7 to 4.8 x 10(5) UFC/ml. In a field-cage experiment, 200 ml of a conidial suspension of Ma2, at a concentration of 2.5 x 10(6) UFC/ml, was applied on 2,500 cm2 soil surface (2 x 10(5) UFC/cm2). The fungus reduced adult emergence, 22% fewer adults emerging in a sandy loam soil, and 43% fewer in loam soil, compared with the controls. M. anisopliae may offer a preferable alternative to chemicals as a biological control agent against A. ludens.