Hadrotrichodes waukheon LaSalle (Hymenoptera: Eulophidae: Tetrastichinae) is a parasite of the citrus peelminer, Marmara gulosa, a persistent pest in the San Joaquin Valley of California (USA) since 1998. Newly discovered morphological variation within the species is reported, including the first description of the male. New biological information including preferred life stage of host for parasitism, clutch sizes, male to female ratios and meconial positioning are included. Field studies demonstrated that one to four adult H. waukheon could emerge from a single M. gulosa larva, and later instar M. gulosa larvae were preferred. Hadrotrichodes waukheon is a gregarious, primary parasitoid and may be a candidate agent for biological control of M. gulosa.