Disposition of Cucurbitacin as a Factor in Host Plant Selection by Diabroticite Beetles and Electrophoretic Analysis of the Coevolved Genus Cucurbita
Ferguson, Jane Ellen
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https://hdl.handle.net/2142/71776
Description
Title
Disposition of Cucurbitacin as a Factor in Host Plant Selection by Diabroticite Beetles and Electrophoretic Analysis of the Coevolved Genus Cucurbita
Author(s)
Ferguson, Jane Ellen
Issue Date
1985
Department of Study
Horticulture
Discipline
Horticulture
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Entomology
Abstract
Five species of Diabroticites with different host plant affinities produced an essentially identical array of metabolites when fed radio-labeled cucurbitacin B. All species excreted the bulk of the cucurbitacin (67.17-94.59% total dpm); permanently sequestered a small proportion of a cucurbitacin D conjugate in the hemolymph (0.98-2.76%); and apportioned the remainder between the gut, the body and the eggs (when present). Markedly different ratios between the excretory metabolites, i.e., polar vs. unmetabolized cucurbitacin, suggest that Diabrotica virgifera virgifera, a grass specialist, and Acalymma vittatum, a cucurbit specialist, have lower rates of metabolic alteration than D. undecimpunctata howardi and D. balteata which are polyphagous and D. cristata.
Mean lifespans for D. balteata and D. v. virgifera, and male A. vittatum decreased significantly with continuous feeding on Cucurbita fruit containing cucurbitacins (vs. fruit devoid of cucurbitacins). The longevity of female A. vittatum, however, was unaffected by the presence or absence of cucurbitacins. Males of four Diabroticite species consumed an average of 27.4% more artificial diet after the incorporation of 0.5 mg cucurbitacin D per g fwt diet whereas female consumption increased only 5.0% on the average.
Four species of Diabroticites were shown for the first time to sequester cucurbitacins. While all beetles fed on an artificial pollen diet with no cucurbitacins were readily consumed by Chinese praying mantids, a significant proportion of adult Diabrotica spp. beetles fed on squash fruit containing cucurbitacins were rejected. Moreover, even when adults did not feed on cucurbitacins, 21-24% of A. vittatum were rejected by the mantids which is consistent with larval sequestration of cucurbitacins. The mantids failed to learn to avoid any of the beetle species despite adverse effects associated with ingestion.
Electrophoretic analysis of Cucurbita isozymes revealed abundant intra- and interspecific variation for nine enzymes. A tree constructed by PAUP character analysis, however, was largely inconsistent with known cross-compatibility relationships. Phenotypes of malate dehydrogenase for C. foetidissima, C. digitata, and C. lundelliana, C. palmata, C. pepo, and C. texana suggest the loss of duplicate enzyme expression in some populations of these species.
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