A new fluorescent compound (5-[[[5- (dimethylamino)-1-naphthalenyl]sulfonyl]-aminol]-1,3-benzodioxole) tested against all instars of larvae of Aedes aegypti (L.) was found to produce morphogenetic effects similar to those produced by synthetic insect growth regulators. Larvae failed to molt completely to the next larval stage, larval-pupal intermediates were formed; or the surviving larvae required more time for pupation.