Disturbance of adult eclosion by fenoxycarb in the silkworm, Bombyx mori

Abstract

Fenoxycarb treatment before and after pupal ecdysis of Bombyx mori disturbed adult eclosion and the animals were unable to escape from the pupal exuviae. This effect of fenoxycarb was dose and time dependent with the highest sensitivity around the pupal ecdysis. The sensitivity rapidly diminished within 20 hours of pupal ecdysis. Twenty-hydroxyecdysone (20E) produced similar effects. Fenoxycarb injection at the pupal ecdysis induced higher ecdysteroid production by the prothoracic glands and higher PTTH-secretory activity in the brain-corpora cardiaca-corpora allata complexes. As a result, the fenoxycarb treated pupae contained higher ecdysteroid titres in the haemolymph. Both the fenoxycarb and the 20E treatments resulted in the lack of development of the rectum in pharate adults. This was the main cause of high ecdysteroid titres in the pharate adult stage. This effect was mimicked by either removal of the rectum early in the pharate adult stage or a surgical extirpation of the hindgut at the time of pupal ecdysis. These results suggest that the disturbance of adult eclosion by fenoxycarb is due in part to the inability of the formation of the rectum in the pharate adult stage.