Physiological basis of ovipositional behaviour in the false ovoviviparous cockroach, Pycnoscelus surinamensis (L.)

The formation of a compact batch of eggs well enclosed in an oöthecal covering and retracted into the brood sac is characteristic ovipositional behaviour of mated Pycnoscelus surinamensis females of the bisexual strain. Virgin females, on the other hand, rarely form a symmetrical oötheca or retract it into the brood sac. It has been shown by mating females to sterile males that the stimuli of copulation and transfer of a spermless spermatophore are not responsible for co-ordinating successful oviposition. Removal of sperm-laden spermathecae results in abortive oviposition indicating that the movement of sperm into the spermathecae is not an adequate stimulus for successful oviposition. Cutting the ducts of the sperm-filled spermathecae, thus preventing release of sperm during egg laying, results in predominantly abortive oviposition. From these experiments it is concluded that the sperm do not exert their influence over successful oviposition hormonally but rather by way of the nervous system. Analysis of the distribution of nerves to the spermathecae and surrounding structures by vital staining with leucomethylene blue shows that small branches of ventral nerve 7 innervate the muscles investing the spermathecae and their ducts as well as the muscles which attach the spermathecal bulb to the common oviduct. Other branches of VN7 innervate the bursa, brood sac, and vagina. Severance of VN7 at the last abdominal ganglion results in abortive oviposition in mated females whereas severance of DN7, which innervates the lateral and dorsal parts of segment seven, does not. From this operation it is concluded that innervated spermathecae are required for successful oviposition.