Microscopic observations have revealed differences among the eggs of species A, B, C and D of the Anopheles dirus complex. The eggs of species A and C are similar in size and shape. They are intermediate in size between the eggs of species B, which is the largest, and that of species D, which is the smallest. The pattern of outer chorionic cells between the frill and the float is species specific. The pattern consists of rows of irregularly shaped cells in species D and different numbers of rows of regularly shaped cells in species A, B and C. Scanning electron microscopy revealed that the deck tubercles are arranged in aggregates which are more widely spaced in species A than in species B. The aggregates are large in species C, of moderate size in species A and B, and small in species D. The egg characters may be useful in separating species A, B, C and D of the An. dirus complex.
