Larvae of Uresiphita reversalis feed almost exclusively on legumes of the tribe Genisteae, whose characteristic secondary metabolites are quinolizidine alkaloids (QA). Aposematic larvae store host plant-derived QA in their integument, while the pupae are almost alkaloid-free. In the last instar larvae, alkaloids were concentrated in the larval head, possibly in the silk glands. About 80% of the alkaloids were transferred to the cocoon silk and 19% were lost with larval exuviae.
The larval alkaloid pattern was characterized by capillary GLC and GLC-MS and compared to that of the host plant, Teline monspessulana. Whereas the host plant contained mainly epiaphylline, dehydroaphylline and aphylline, larvae selectively accumulated N-methylcytisine, a relatively minor component of the plant QA; the faeces contained mainly epiaphylline and dehydroaphylline. Thus uptake and sequestration must be selective processes. Uptake by isolated larval midguts was time-, pH- and temperature-dependent and displayed an activation energy between 50 and 80 kJ/mol. Furthermore the in vitro uptake of 13-hydroxylupanine was competitively inhibited by cytisine. All these data provide evidence that QA uptake does not proceed by simple diffusion but instead with the aid of a carrier mechanism; this could explain the differential alkaloid uptake observed in living larvae.
© 1946 – 2014: Verlag der Zeitschrift für Naturforschung
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