Induction of perfect superlarvae by the application of juvenile hormone analogue to starved larvae of the silkworm,Bombyx mori

Topical application of juvenile hormone analogue, methoprene, induced a supernumerary larval moult in the silkworm, Bombyx mori. The incidence changed greatly depending on developmental stages and physiological states of the methoprene-treated larvae. When methoprene was applied to feeding larvae, only those treatments from the middle of the 2nd instar until the middle of the 4th instar were effective. An 18-h starvation period from the beginning of the 4th instar and a dose of 1 μg of methoprene per larva were required for 100% incidence of the perfect superlarvae. Allatectomy had no effects on the induction of superlarvae by methoprene. The treated 4th-instar larvae ecdysed to the 5th instar without any delay compared to the controls, and underwent an additional larval ecdysis 4.5 days later. The induced 6th-instar larvae took 8.5 days until the onset of cocoon spinning. The induced superlarvae showed reduced growth rates but an increase of final mass due to prolonged feeding period. A sharp but reduced peak in ecdysteroid titre in the haemolymph appeared one and a half days prior to each larval ecdysis in the treated larvae, suggesting that methoprene provokes the extra larval moult through an additional release of ecdysteroids.