BIOLOGICAL-ACTIVITY OF MARMESIN AND DEMETHYLSUBEROSIN AGAINST A GENERALIST HERBIVORE, SPODOPTERA-EXIGUA (LEPIDOPTERA, NOCTUIDAE)

No significant effects were observed in bioassays designed to measure impact of the furanocoumarin precursors demethylsuberosin and marmesin on typical physiological parameters (survival and development rate) o f the generalist herbivore, Spodoptera exigua (Hubner). The linear fur anocoumarin psoralen did increase developmental times and reduce survi val. All of these compounds were demonstrated to have significant beha vioral (feeding deterrence) effects against both first and third insta rs of S. exigua in diet-incorporation bioassays. In tests initiated wi th first instars, significantly (P < 0.05) more larvae preferred contr ol diet to diet containing marmesin or psoralen on all five sample dat es; control diets were significantly preferred to diets with demethyls uberosin on three of five sample dates. Similar results were observed for tests initiated with third instar larvae, but the avoidance of dem ethylsuberosin-containing diets was stronger. Therefore, assaying fura nocoumarin precursors just for effects on growth and survival may not provide an accurate picture of the ecological importance of these comp ounds.