Effects of Diflubenzuron on Chitin Synthesis in the Postmolt Blue Crab Callinectes Sapidus : A Morphologic Study Using an in Vitro Explant Culture System

Abstract

Diflubenzuron is an insect larvicide that inhibits chitin synthesis. The effects of diflubenzuron were investigated on a nontarget organism, the postmolt adult blue crab Callinectes sapidus. Sections (explants) of the cuticle and epithelium were cut from the dorsal carapace of freshly molted blue crabs and maintained for 6 h in a buffered Ringer's solution containing diflubenzuron and 3H-glucosamine. Control sections were taken from the same animals and were maintained in a like fashion but without exposure to diflubenzuron. The sections were subsequently fixed, processed and examined by electron microscopy, or probed with a chitin oligosaccharide-binding lectin, or studied for 3H-glucosamine incorporation by autoradiography. Ultrastructurally, diflubenzuron-treated tissues showed coarse clumping of nuclear chromatin, dilation of the rough endoplasmic reticulum, and vesiculation of the apical cytoplasm of the cuticular epithelial cells. Decrease in nascent chitin in the treated tissues was demonstrated at the light microscopic level by scant binding of the lectin and minimal radiolabeling in the endocuticular region. The results offer morphologic evidence that diflubenzuron can interfere with crustacean chitin synthesis.