Egg shells of mallophagans and anoplurans (Insecta: Phthiraptera): morphogenesis of specialized regions and the relation to F-actin cytoskeleton of follicular cells.

The egg shells of investigated phthirapterans consist of three basic elements: an anterior operculum, a main egg shell and a posterior hydropyle. In some species these elements show further regional specializations: bristles and projections that facilitate attachment to feathers of the host, micropyles and aeropylar openings. All of the egg shell specializations are formed by distinct subpopulations of follicular cells. Staining with rhodamine-conjugated phalloidin has revealed that these subpopulations significantly differ in the distribution of microfilaments (F-actin). In this respect four morphological categories of the follicular cells have been distinguished: (1) cells devoid of processes and microvilli, with basal arrays of microfilaments, responsible for the secretion of a flat chorion; (2) cells devoid of processes and microvilli, separated by intercellular spaces, with basal arrays of microfilaments, responsible for the secretion of attachment structures; (3) cells equipped with actin-containing processes, responsible for the formation of micropyles or aeropyles, and (4) cells equipped with bundles of microvilli, responsible for the formation of hydropyles.