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

Chromosaponin I (CSI), a gamma-pyronyl-triterpenoid saponin isolated from pea 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 substance for the blowfly, Phormia regina. The blowfly has taste chemosensilla on the labellum. The sensory receptor cells in the chemosensillum are highly specialized for the tastes of sugar, salt and water, respectively. Application of CSI induced the feeding response of blowflies including full proboscis extension. CSI also induced impulses of the sugar taste receptor cell in the LL-type sensillum. The optimum concentration of CSI in these responses was 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 sucrose in stimulating the sugar taste receptor cells. CSI-induced impulses appeared after a significant latency compared with sucrose. As far as we know, this is the first report describing that a natural saponin induces sugar responses in insects. CSI is a unique saponin because of its bifunctional property in plants and insects.