A study of the chorion of the egg of Psorophora columbiae (Dyar and Knab) (Diptera: Culicidae)

Typescript (photocopy).The morphology of the chorionic layers of the eggs of Psorophora columbiae (Dyar and Knab) mosquitoes was studied by scanning and transmission electron microscopy during a period of time when eggs were in a predeposition state in the ovary, and again when the eggs were in a post-deposition state after leaving the confines of the mosquito. Results of these studies indicate that several changes in the appearance of the chorionic layers of fully developed ova of Ps. columbiae occur shortly after the eggs are deposited in the environment. Patterns of the inner chorionic sculpturing were observed by SEM on the anterio-lateral surfaces of 491 eggs of Ps. columbiae collected at 10 different geographic locations in the United States. The eggs deposited by mosquitoes in California had 3 unique patterns which gave evidence to support the theory that the species of Psorophora from California presently identified as Ps. columbiae may be a different species from the eastern one which occurs in Arkansas, Florida, Louisiana, Mississippi, New Jersey and Texas. It was further determined that the inner chorionic patterns, frequency of occurrence of these patterns and the thickness of the inner chorion of eggs from the eastern populations of Ps. columbiae cannot be used to identify the geographic area where the adults that deposited eggs occur or to determine the seasons of the year when the eggs of this species were deposited. Oviposition behavior of gravid Ps. columbiae mosquitoes was observed and photographed in the laboratory. The behavioral movements of ovipositing Ps. columbiae females can be subcategorized into preoviposition, oviposition and post-oviposition activities. The primary oviposition sites of gravid Ps. columbiae females were found to be in the cracks and holes of clay and silt loam soils. The eggs of this species were positioned in holes in such a manner as to have the anterior end of the egg directed toward the surface of the soil. The dorsal sides of these eggs were usually attached to the soil wall by means of the outer chorion