THE OCCURRENCE OF TWO MALE FORMS, DICHOPTIC AND HOLOPTIC, INSIMULIUM EXIGUUMROUBAUD (DIPTERA, SIMULIIDAE)

Abstract

Every student of entomology is familiar with the remarkable sexual dimorphism displayed by simuliid flies. There are not only striking differences in the coloration of the sexes, but also numerous morphological ones, as the different shape of the thorax, the different form of the claws, of the mouth organs, and especially of the eyes, which, dichoptic in the female, are holoptic in the male and are here sharply divided into an upper part with large facets and a lower strongly pigmented part with small ones.