PHOTOTOXICITY OF THE ALLELOCHEMICAL, ALPHA-TERTHIENYL, TO LARVAE OF MANDUCA-SEXTA (L) (SPHINGIDAE)

.alpha.-Terthienyl, a common chemical constituent in the Asteraceae, was administered to 5th stadium larvae (Day 1) of the tobacco hornworm, M. sexta (L.) by incorporation into artificial diet and by topical application. Toxicity toward larvae was elicited by simultaneous exposure to this allelochemical and UV-A irradiation (320-400 nm). Larval treatment with either .alpha.-terthienyl or UV-A irradiation alone caused no apparent adverse effects. A single, ingested dose of .alpha.-terthienyl (50 .mu.g g larval weight-1), followed by irradiation for 4 h, resulted in delayed and abnormal pupal formation with no subsequent adult emergence. Topical application of the plant compound (50 .mu.g g-1) and UV-A irradiation led to tissue necrosis that affected both sclerotization and melanization of the pupal case in later development.