Abstract
Induction of furanocoumarins, toxic and antifeedant secondary compounds, in wild parsnip, Pastinaca sativa L., was examined to assess the efficacy of inducible defenses and to assess whether in the case of wild parsnip the induction response is likely to represent an adaptation to herbivory. Leaflets of undamaged plants were experimentally damaged by Trichoplusia ni, a generalist folivore that occasionally feeds on wild parsnip. Intact and damaged leaflets were then measured to obtain constitutive and induce levels of furanocoumarin. In a separate experiment, levels of furanocoumarin in manually damaged leaflets were compared with intact leaflets. Both insect and manual damage induced furanocoumarin production in leaves of wild parsnip. Larvae of T. ni, moreover, grew only a fourth as rapidly on induced leaflets compared to non—induced leaflets from the same leaf. By feeding larvae artificial diets containing two of the furanocoumarins in amounts equivalent to constitutive or induced plant levels, I found that furanocoumarin induction can account for much of the reduced larval growth association with induction in intact plants.
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