Adaptations to Furanocoumarins of Pastinaca Sativa by Depressaria Pastinacella (Lepidoptera: Oecophoridae)
Nitao, James Kenji
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https://hdl.handle.net/2142/71106
Description
Title
Adaptations to Furanocoumarins of Pastinaca Sativa by Depressaria Pastinacella (Lepidoptera: Oecophoridae)
Author(s)
Nitao, James Kenji
Issue Date
1987
Doctoral Committee Chair(s)
Berenbaum, May
Department of Study
Entomology
Discipline
Entomology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Entomology
Abstract
Furanocoumarins are plant secondary compounds toxic to a wide variety of organisms. In the wild parsnip, Pastinaca sativa (Umbelliferae), these compounds are most concentrated in the floral parts. Despite these allelochemicals, the parsnip webworm, Depressaria pastinacella (Lepidoptera: Oecophoridae), feeds almost exclusively on the floral parts of this plant and of certain other umbellifers containing furanocoumarins. The allocation patterns of the furanocoumarins in the wild parsnip and the mechanisms by which the parsnip webworm circumvents the toxicity of these compounds were investigated.
Optimal defense theory predicts that within-plant allocation of defensive compounds should reflect the value of plant tissue in terms of its relative contribution to fitness. Consistent with this theory, furanocoumarins were more concentrated in floral units whose loss would have a greater negative impact on subsequent total seed production.
Damage simulating herbivory was tested as an inducer of furanocoumarins in the floral parts of P. sativa. Primary umbels were partially deflorated; the higher order umbels and the remaining primary umbel flowers were then sampled. Total furanocoumarin concentration was not significantly affected by defloration, but one furanocoumarin increased in the secondary umbels of damaged plants. In a second experiment, primary umbels were completely deflorated and the higher order umbels allowed to set seed. No significant effect of defloration on the furanocoumarin content of these seeds was found.
To test the effects of furanocoumarins on D. pastinacella, a procedure for establishing a laboratory colony of this insect was developed. The parsnip webworm is unaffected by the linear furanocoumarin xanthotoxin, a compound toxic to many polyphagous herbivores. This insect metabolizes nearly all of the administered xanthotoxin. Although most of the unmetabolized xanthotoxin and the metabolites are eliminated in the frass, a small amount is excreted in the silk. In vitro experiments suggests that cytochrome P-450 monooxygenases in the microsomal fraction of the midgut are involved in the detoxification of xanthotoxin; these enzymes possessed high specific activity for this furanocoumarin. Moreover, xanthotoxin induced microsomal enzymes that in turn metabolize this allelochemical. Angelicin, a compound toxic to a herbivore adapted to feeding on linear furanocoumarins, had no effect on the parsnip webworm.
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