The Function of Insect Trapping by Penstemon Digitalis and Cirsium Discolor
Thomas, Patricia Ann
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https://hdl.handle.net/2142/77627
Description
Title
The Function of Insect Trapping by Penstemon Digitalis and Cirsium Discolor
Author(s)
Thomas, Patricia Ann
Issue Date
1988
Doctoral Committee Chair(s)
Willson, Mary F.,
Department of Study
Ecology, Evolution, and Conservation Biology
Discipline
Ecology, Evolution, and Conservation Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Botany
Biology, Ecology
Language
eng
Abstract
The capture of insect by sticky secretions occurs in many plant species in many plant families throughout the world. In a few cases such insect-trapping plants have been shown to be carnivorous, e.g., Drosera spp. and Pinguicula spp., and in some cases they have been shown to provide defense against herbivores. In most plants, however, the function of such insect-trapping is not known. In two herbaceous plants native to central Illinois, Penstemon digitalis Nutt. (Scrophulariaceae) and Cirsium discolor (Muhl) Spreng (Compositae), sticky substances that capture insects are produced in the inflorescences. I tested four hypotheses as to the function of insect-trapping in these two plant species: (1) Direct defense against herbivores; (2) Indirect defense against herbivores by attraction of predatory arthropods; (3) Direct nutrition of the plant by digestion and absorption of insects in the trap areas; and (4) Indirect nutrition by absorption of products of decay leached into the ground from the captured insects.
Observations and experimental trap occlusion revealed little evidence that the sticky-traps provide effective defense against herbivores in either plant species. Although predatory arthropods were sometimes present on the inflorescences, more occurred on inflorescences with occluded traps than on those that captured insects, and in C. discolor an increase in predators was associated with a decrease in seeds. Thus, neither defense hypothesis was upheld.
Digestive enzymes were found to be present in the sticky secretions of both plant species, and studies using radioactive fruit flies revealed digestion, uptake, and transport of nutrients from fruit flies on the sticky-traps. There was limited uptake from radioactive fruit flies on the soil. Insect capture produced enhancement of reproduction, and this occurred in various soils, with or without substrate fertilization. The amounts of N and P in the captured insects were sufficient to supply most (80-100%) of the N and P in the seeds of P. digitalis, but only a small proportion (2-3%) of N and P in seeds of C. discolor.
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