Effects of lignoids on a hematophagous bug, Rhodnius prolixus: feeding, ecdysis and diuresis

The effects of lignoids on feeding, ecdysis and diuresis in fourth-instar l arvae of Rhodnius prolixus (Hemiptera) were investigated. Up to 100 mug/ml burchellin, podophyllotoxin, pinoresinol, sesamin, licarin A, or nordihydro guaiaretic acid (NDGA) in the diet did not induce antifeedant effects. Pino resinol and NDGA significantly inhibited ecdysis. In experiments in vivo, b urchellin and podophyllotoxin reduced the production of urine after feeding . 5-Hydroxytryptamine (5-HT), a diuretic hormone, partially counteracted th is effect of burchellin. In experiments in vitro, using isolated Malpighian tubules, (i) burchellin reduced diuretic hormone levels in the hemolymph b ut not the amount of diuretic hormone stored in the thoracic ganglionic mas ses (including axons), (ii) burchellin decreased the volume of urine secret ed by isolated Malpighian tubules, and (iii) 5-HT could not overcome the ef fect of burchellin upon the Malpighian tubules. We conclude that burchellin interfered with the release, but not with the production of diuretic hormo ne by the thoracic ganglionic mass or induced an antidiuretic hormone and d irectly affected the Malpighian tubules. (C) 2000 Elsevier Science Ltd. All rights reserved.