Light-mediated allelochemical effects of naturally occurring polyacetylenes and thiophenes from asteraceae on herbivorous insects

Polyacetylenes and their thiophene derivatives, characteristic secondary metabolites of the Asteraceae, were examined for their effects on herbivorous insects. Three thiophenes (a monothiophene, a bithiophene, and -terthienyl) and four polyacetylenes (phenylheptatriyne, phenylheptadiynene, phenylheptadiyene acetate, and matricaria lactone) were studied for their phototoxicity and light-independent toxicity to (1) a polyphagous lepidopteran,Ostrinia nubilalis, whose host range includes a number of phototoxic Asteraceae, (2) a polyphagous lepidoteran,Euxoa messoria, whose host range includes very few species of Asteraceae, and (3) an oligophagous lepidopteran,Manduca sexta, which is a specialist on Solanaceae. Several compounds were phototoxic toM. sexta andE. messoria even at very low irradiance levels, but behavioral adaptations, including spinning silk and boring into diet, allowedO. nubilalis to avoid photosensitization. Light-independent activity of the compounds to all three species involved feeding deterrence increasing in the orderO. nubilalis, E. messoria, andM. sexta, and longterm metabolic toxicity in the form of impaired nutrient utilization. The biosynthetically derived thiophenes were more toxic than their acetylenic precursors, and toxicity increased with increasing number of thiophene rings. The results are discussed in terms of plant-insect coevolution.