Chromosaponin I stimulates the sugar taste receptor cells of the blowfly, Phormia regina

Chromosaponin I (CSI), a gamma-pyronyl-triterpenoid saponin isolated from p ea and other leguminous plants, stimulates the growth of roots in a variety of plants. In the present work, we introduce CSI as a sugar taste substanc e for the blowfly, Phormia regina. The blowfly has taste chemosensilla on t he labellum. The sensory receptor cells in the chemosensillum are highly sp ecialized for the tastes of sugar, salt and water, respectively. Applicatio n of CSI induced the feeding response of blowflies including full proboscis extension. CSI also induced impulses of the sugar taste receptor cell in t he LL-type sensillum. The optimum concentration of CSI in these responses w as 0.1 mM which is much lower than that of sucrose. Based on the comparison of dose-response relationships, CSI is 100 times more effective than sucro se in stimulating the sugar taste receptor cells. CSI-induced impulses appe ared after a significant latency compared with sucrose. As far as we know, this is the first report describing that a natural saponin induces sugar re sponses in insects. CSI is a unique saponin because of its bifunctional pro perty in plants and insects. (C) 2000 Elsevier Science Inc. All rights rese rved.