Alfalfa (Medicago sativa L.) is attacked by pests that cause serious damage when not controlled. Among the insect pests are pea aphid, Acyrthosiphon pisum Harris; spotted alfalfa aphid, Therioaphis maculata Buckton; armyworm, Spodoptera exigua Hübner; alfalfa leafhopper, Empoasca fabae Harris; and three-cornered alfalfa hopper, Spissistilus festinus Say. In the Comarca Lagunera, insecticides seldom are used to control alfalfa pests that are regulated by beneficial insects. However, species that provide this service are little known. The objective of this study was to identify Trichogrammatidae collected with a sweep net each week from 3 March to 30 December 2011 in an alfalfa plot at the Unidad de Producción 18 de Julio at Universidad Autonoma Chapingo at Bermejillo, Durango. Species identified were Aphelinoidea nr. roja Triapitsyn 2005; Oligosita sanguina Girault 1911; Paracentrobia punctata Howard 1897; Ufens nr. simplipenis Owen 2005; and Trichogramma pretiosum Riley 1879. A. nr. roja, O. sangunea, P. punctata, T. pretiosum, and U. nr. simplipenis on alfalfa are new records for Mexico. With the exception of T. pretiosum, the other species are pest insects with sucking habits.