Effects of fenoxycarb, nerve-section and farnesoic acid on corpus allatum activity in adult female Periplaneta americana

Abstract

Adult female Periplaneta americana were topically treated with 100 μg of the juvenile hormone analogue fenoxycarb, and given food containing 100 ppm of fenoxycarb. Treatment led to increased rates of oötheca production and a simultaneous decrease in juvenile hormone III biosynthesis by the corpora allata. During a single reproductive cycle, corpora allata from control animals showed low rates of synthetic activity at the beginning and end of the cycle but were highly active at the middle of the cycle. In fenoxycarb-treated animal, corpora allata showed very little synthetic activity throughout the reproductive cycle though there was a slight increase around the cycle mid-point. Sectioning of the nervi corporis cardiaci I and II and nervi corporis allati I had no effect in controls but, in treated insects, nervi corporis allata I section resulted in a significant increase in corpus allatum activity, though not to control levels. Incubation with farnesoic acid had no effect on high-activity glands isolated from control insects at the mid-point of a reproductive cycle but caused a substantial increase in juvenile hormone biosynthesis by low-activity control glands isolated at the start of a cycle. Glands from fenoxycarb-treated insects were significantly stimulated by farnesoic acid but biosynthetic activity was still lower than in controls.