Comparative Ultrastructure of the Compound Eye of the Wild, Laboratory-Reared, and Irradiated Mediterranean Fruit Fly, Ceratitis capitata (Diptera: Tephritidae)1

Abstract

The compound eye of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), was found to consist of ca. 3,000 ommatidia, each composed of a dioptric apparatus overlying a cluster of eight retinula cells. A cross-section of the cell cluster reveals an open rhabdom structure with a superior R7 central cell and an inferior R8 central cell similar to that of other cyclorrhaphous Diptera. Each ommatidium has a pair of primary pigment cells and 12 shared longitudinal pigment cells. The dimensions and histology of all ommatidial components are described briefly. Various ultrastructural differences occur between wild and laboratory-reared flies. Laboratory-reared, particularly pupal-irradiated, flies have ommatidia comprised of less tightly packed retinula cells, and rhabdomeres that are consistently smaller, occasionally absent, and more peripherally distributed within the ommatidial cavity than those in wild flies. The R7 rhabdomere is sometimes expanded into a bulb at the level of the Rl-7 nuclei in laboratory-reared flies, but not in wild flies. Ommatidial cavities of laboratory-reared flies are enlarged and often contain inclusions not present in wild flies. The cytoplasmic density and concentrations of large lipid globules is reduced in the longitudinal pigment cells of laboratory-reared flies. The pattern of increasing ultrastructural deviation from the wild condition in laboratory-reared and irradiated flies is consistent with, and indeed provides a basis for, explaining a pattern of decreasing spectral sensitivity (wavelengths 350 to 750) found electroretinographically for flies obtained from the same samples.