TOXICITY OF LINEAR FURANOCOUMARINS TO SPODOPTERA-EXIGUA - EVIDENCE FOR ANTAGONISTIC INTERACTIONS

The linear furanocoumarins psoralen, bergapten, and xanthotoxin were t ested for toxicity to the beet armyworm Spodoptera exigua (Hubner) und er short ultraviolet (UVB) radiation. Increased dietary concentrations of each furanocoumarin significantly decreased insect larval weight, extended generation time, and induced higher mortality. Xanthotoxin wa s the most toxic, followed by psoralen and bergapten. Combining psoral en with bergapten, xanthotoxin, or both resulted in significantly anta gonistic effects on insect mortality. The combination of bergapten and xanthotoxin, however, produced additive effects. The implications of these observations for S. exigua resistance in the wild plant accessio n of Apium prostratum and the enigma the findings represent for plant- insect relationships are discussed.