Patterns of pigmentation in abdominal tergites 2 and 3 of adult female Culicoides variipennis (Coquillett) were examined for changes associated with blood feeding. Six tergite types were identified that allowed separation of nulliparous from parous flies based on pigmentation. In colonies of flies from Texas and Idaho, nulliparous flies had open posterior margins that contained 2 long unpigmented areas that extended anteriorly nearly the length of the tergite; field-collected flies from Colorado had an additional pigmented spot in each unpigmented area. Patterns that developed after a blood meal were characterized by closed posterior margins that appeared smooth or slightly wavy. These patterns were developed before the blood meal was fully digested and remained constant for the life of the fly; additional blood meals did not change the types. The classification of tergite types in C. variipennis was easy, worked with alcohol-preserved flies without sugar meals, and distinguished parous from nulliparous females with 98% accuracy.
