Disruption of Aleurocanthus woglumi Ashby, the citrus black fly (CBF) parasitoid populations in Northeast Mexico and Southeast Texas, resulted in a severe problem on citrus orchards in 1988, 1999, 2002, 2003 and 2004. CBF now is the most important citrus pest in the State of Tamaulipas with an infested area of 1,584 ha, and 3,868 ha in Nuevo León, diminishing fruits production and quality with repercussions on commercialization and reduction of citrus farmers economics. In Mexico and all the world, the main control of this pest is Biological Control and the main natural enemy in Northeast México (Tamaulipas and Nuevo Leon) and Southeast Texas (Hidalgo and Cameron Counties) was Encarsia perplexa Huang and Polaszek. Amitus hesperidum was present only with few specimens. In one study from March to June, 2004, seasonal abundance of E. perplexa in one citrus orchard of the Municipality of Guemez, Tamaulipas, presented during 2004 two peaks inmmediately after the CBF abundance peak during April/07/04 and May/12-26/04, being high in May and more extended. The seasonal abundance was measured accounting parasitoids with an average of 5.69 leaves in 4 shoots of each tree, where the tree presented 100% of CBF infestation. Higher populations of parasitoids was observed on the west side of the tree; females were more abundant than males.