The inductors of differentiation of prefollicular tissue and the follicular epithelium in ovarioles of Pyrrhocoris apterus (Heteroptera).

Differentiation of the tissues of the telotrophic ovarioles from the embryonic primordium occurs gradually throughout larval development of bugs. All tissues are established already at the beginning of the last larval stage as observed by Wick & Bonhag (1955) in Oncopeltus fasciatus. During the last instar, when the corpora allata are morphogenetically inactive, the synthetic activity of the cells of first ovarian nutritive system, the trophocytes, takes place. The nutrients released by trophocytes at the final emergence activate the oocytes, starting previtellogenesis (Masner, 1966). The function of this nutritive system is known to be independent of any humoral control (Wigglesworth, 1936, and others). Food intake seems to be the only inductor of trophocyte growth. The developing oocyte grows into the prefollicular syncytium. The surrounding tissue starts to organize into a unilayered epithelium. The renewal of corpus allatum activity and the release of the juvenile hormone (JH) is necessary for further vitellogenesis. The follicular epithelium, representing the second nutritive ovarian system, has to be activated by the hormone (Wigglesworth, 1936; Pfeiffer, 1936, 1939; Joly, 1945; Engelmann, 1959; Joly, 1960; Highnam, Lusis & Hill, 1963; Slama, 19646). The activated cells play an important role in supplying the oocyte with yolk, forming material either regulating or assisting in the transmission of yolk precursors from the blood (Telfer, 1965). Thus JH exerts a direct control of oogenesis, whereas the activation hormone (AH) from the neurosecretory cells is said to regulate this process only indirectly, by making materials available for vitellogenesis (Highnam, 1964). Oogenesis is inhibited after previtellogenesis in the absence of JH, i.e. when the first nutritive system should be replaced by the second one. The oocytes