Celery, 'Apium graveolens', produces three phototoxic linear furanocouarins (LFCs) that can cause a photodermatitic reaction in humans in the presence of UV radiation. LFCs are toxic to numerous organisms and are both constitutively produced and induced in response to several abiotic and biotic. stresses. Induction of LFCs by the tarnished plant bug, ' Lygus lineolatis' (TPB) and the cabbage looper, 'Trichoplusia ni', and effects of LFCs on growth and development of TPB and the parasitoid 'Persitenus stygicus' were examined. Both insects induced LFCs in celery, but concentrations in petioles rarely reached levels capable of causing photodermatitis. Developmental rates of TPB were affected by ingestion of LFC-containing diet. However, other factors are likely to account for the differences observed between nymphs fed damaged and undamaged celery tissue. The data suggest that other compounds in celery petioles may be of value to breeding programs involved in the development of insect-resistant genotypes.