Chorionic Structure of the Egg of the Screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae)

Abstract

The chorion of the Cochliomyia hominivorax (Coquerel) egg is described using observations from scanning and transmission electron microscopy and light microscopy. Included are the gross structure and surface characteristics of the chorion, the basic architecture and internal components of the chorion proper, the location and function of the hatch lines, and the functional morphology of the plastron region as a respiratory structure. In the regular hexagonal arrangement and form of individual structural units, the chorion of the screwworm egg exhibits basic architectural features common to other higher Diptera. Within the open spaces of the endochorionic layer, however, are previously undescribed membranous structures of unknown function which appear to line the cavities of the endochorion. The plastron region partially encircles the micropyle (anterior end) of the egg and extends along the dorsal surface to the posterior pole; it is delineated laterally by the hatch lines. The chorion ruptures along the anterior region of the hatch lines as the larva emerges. The plastron region is composed of elaborate stalked aeropyles above a highly dissected inner reticulum. This structure is believed to function as a respiratory organ when the egg is immersed in fluid.

Fine Structure of the Eggshell of the Blow Fly,Lucilia cuprina

“…cuprina conforms to general ultrastructural patterns shown by SEM micrographs of blow fly species (Kitching 1976; Erzinclioglu 1989; Liu and Greenberg 1989; Peterson and Newman 1991; Greenberg and Singh 1995; Sukontason et al 2004b), by bearing the dorsal plastron, micropyle and polygonal pattern of chorionic sculpture. The relatively wide plastron and slight bifurcation of the plastron near the micropyle of L .…”

Ultrastructure of eggshell of Chrysomya nigripes Aubertin (Diptera: Calliphoridae)

“…7) and external hexagonal chorionic sculpture (Fig. 5) observed in C. nigripes, agreed with that recorded in the C. hominivorax egg reported by Peterson and Newman (1991). The function of the C. nigripes eggshell must fulfill several significant proposes including protection of the developing embryo from the environment, and the ability of sperm entry and gas exchange (Margaritis 1985).…”

“…However, this study indicated that the most distinct feature of the C. nigripes eggs was the chorionic sculpture, which bore a markedly elevated boundary in hexagonal pattern. This is different to the indistinct boundary observed in many blowfly species, e.g., Chrysomya bezziana Villeneuve, C. varipes (Macquart), C. rufifacies (Macquart), C. albiceps (Wiedemann), C. megacephala (F.), C. saffranea (Bigot), C. chloropyga (Wiedemann), Cochliomyia hominivorax (Coquerel) and C. macellaria (F.) (Kitching 1976;Peterson and Newman 1991;Greenberg and Singh 1995). Kitching (1976) Figs.…”

“…The multi-layered eggshell of C. nigripes exhibited similar structures to those previously reported in the members of blowfly (Hinton 1960;Peterson and Newman 1991), fruit fly or other insect groups (Margaritis 1985). The non-perforated exochorion, as well as the corresponding hexagonal pattern of the pillar layer ( Fig.…”

The fowl tick, Argas (Persicargas) persicus (Ixodoidea: Argasidae): Description of the egg and redescription of the larva by Scanning Electron Microscopy

“…Elzinga (1987) reported that the chorion, which was secreted from the ovarian wall following surrounding of the oocyte with yolk before its release into the oviduct, gives the characteristic species shape and covering of the egg. The structure of the chorion was previously used to differentiate between species of May fly (Peterson and Newman 1991) and blow fly (Sukontason et al 2004).…”