Atypical secondary compounds in the family cruciferae: tests for toxicity to pieris rapae, and adapted crucifer-feeding insect
1983
USHER, BARBARA F. | FEENY, PAUL
In addition to the glucosinolates typical of the family, some cruciferous plants contain atypical secondary compounds such as alkaloids, cucurbitacins, and cardenolides. Some of these, or close analogs, were tested for toxicity to larvae of Pieris rapae, which normally feeds on glucosinolate-containing plants. Growth was measured as a function of food consumption, and larvae fed experimental chemicals or plant extracts were compared with those fed a control diet. Compounds assayed were k-strophanthin, lunarine (an alkaloid from seeds of Lunaria annua), and a mixture of cucurbitacin I and cucurbitacin E; in addition, two extracts of Lunaria annua leaf were assayed. Compounds were tested at concentrations that have been measured in plant material. No evidence of toxicity was found for any compound or extract at the levels tested. Growth for a given consumption was actually increased relative to the control for the larvae fed k-strophanthin and for those fed the mixture of cucurbitacins E and I. Actual consumption was significantly depressed relative to controls on diet containing an ethanol extract of L. annua leaf. It was concluded that none of the tested atypical compounds are effective as toxicological defenses against P. rapae larvae, although compounds present in the ethanol extract of L. annua leaf may deter feeding. The seed alkaloid lunarine was present in cotyledons of Lunaria annua after germination, but it was not detected in roots or in foliage leaves.
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