Acceleration of pupal-adult development by fenoxycarb in the silkworm, Bombyx mori

Treatment by fenoxycarb (> 0.1 mug/animal) during a short developmental period in the pharate pupal stage of the silkworm, Bombyx mori, induced alterations in the normal pupal-adult development. All fenoxycarb-treated animals showed accelerated development and precocious adult cuticle deposition very early in the pupal stage. Various internal and external organs of the developing adults underwent abnormal differentiation and were extensively malformed. Consequently, pupal-adult development and adult eclosion behaviour were disturbed. Similar effects were induced by injections of high doses (greater than or equal to 4 mug/animal) of 20-hydroxyecdysone (20E) only around the time of pupal ecdysis. Treatment with 1 mug of fenoxycarb in the pharate pupal stage did not affect haemolymph ecdysteroid titers early in the pupal stage. Our results, therefore, suggest that fenoxycarb, a potent juvenile hormone mimic, can imitate the developmental effects of excess 20E and behave as an ecdysteroid mimic after its application during the short developmental period of the pharate pupal stage of B. mori. These results shed light on the timely and coordinated increase of endogenous juvenile hormone titer before pupal ecdysis.