Egg shells in mites: vitelline envelope and chorion in Acaridida (Acari)

Abstract

Witalifiski, W., 1993. Egg shells in mites: vitelline envelope and chorion in Acaridida (Acari). Exp.Appl. Acarol., 17: 321-.344.This study deals with the formation of vitelline envelope (VE) and chonon compartments in several free living and parasitic acaridid mites. In all investigated mites, the VE is of primary origin (produced by oocyte itself), whereas exochorion material is of tertiary, origin (oviduct or chorion gland .secretion).In acarid mites Acarus siro and Tyrophagus perniciosus, VE formation starts with the oviductal oocytes in which vitellogenesis already proceeds. It is characterized by stratification (Acarus) or coarse fibrillar texture (Tyrophag~). Oocyte microvilli penetrating VE material were not observed. When the vitellogenesis terminates, VE becomes homogeneous and is transformed into chorion. This is the only layer protecting the deposited egg in A. siro, whereas in T. perniciosus the chorion-coated eggs passing through the distal portion of the oviduct are additionally covered by exochorion material deposited in three distinct forms: dense patches, granules, and most conspicuous tocular chambers.In Tyrophagus longior, the egg surface closely resembles that of T. perniciosus, but the locular chambers are smaller. In Aleuroglyphus ovatus the exochorion material forms tiny spherical patches instead of locnlar chambers.In Sarcoptes scabiei, Notoedres cati and Falculifer rostratus, flocculent VE appears on vitellogenic oocytes in the oviduct. VE development is characterized by formation of numerous lenticular perivitelline spaces, which initially grow to disappear later. Then VE material transforms into fully homogeneous chorion. Chorion glands in Sarcoptes and Notoedres produce multivesicular secretory bodies; their content is released onto the egg surface to form a vesicular monolayer (exochorion) during the egg passage. The chorion gland in Falculifer is composed of two secretory cell types. Its secretion possibly glues the eggs to the host feather barb during highly ordered deposition, and forms the appendage ending with a fibbed plate, here considered to be a print of female undulate lamina acting as an ovipositor. The hatching suture is present. Neither distinct micropyle nor aeropyles have been found in eggs of species under study.The exochorion is proposed to be an adhesive layer which fixes the eggs to the substratum. The same role plays the chorion gland secretion in F. rostrat~. It can be argued, however, that locular chambers of Tyrophagus exochorion may participate in reduction of water loss rather than in egg adherence or plastron respiration, as previously suggested in the literature.

Acaricidal and quantitative structure activity relationship of monoterpenes against the two-spotted spider mite, Tetranychus urticae

“…The lack of ovicidal activity of natural monoterpenes seems in accordance with the view that the exochorion of mite eggs functions as a barrier against desiccation, as suggested by Witalinski (1993) or against vapor uptake. Thus, the higher acaricidal activity in our results on adult T. urticae might be related to desiccation.…”

Effects of relative humidity on development, fecundity and survival of three storage mites

“…In addition, the lower mortality observed for the egg stage and the lesser effect on their developmental times with regard to larvae, despite of the similar size, are related to the barrier function of the chorion of eggs. In the case of Tyrophagus species this effect is improved as their eggs present and extra layer called exochorion with specific activity against desiccation (Witalinski 1993).…”

Ultrastructural Morphology of the Male and Female Genital Tracts of Psoroptes spp. (Acari: Astigmata: Psoroptidae)

“…Unfortunately, no accurate data are available on the mode of vitellogenesis in the genus Psoroptes. By analogy with observations realized in other Psoroptidia (Witalinski 1993), it can be supposed that the vitelline envelope is produced by the oocyte itself and that exochorion, proposed to be an adhesive layer which fixed the eggs to the substratum, is of uterus (chorion gland) secretion. No secretory aspect was observed in the oviduct of Psoroptes.…”