Date of Award:

5-1-1976

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Ting H. Hsiao

Committee

Ting H. Hsiao

Committee

Thomas Farley

Committee

James MacMahon

Committee

Ivan Palmblad

Abstract

The purpose of this study was to examine the carotenoids of species within the genus Leptinotarsa and their host plants, with the anticipation that a knowledge of the pigments and their distribution would aid in understanding the evolutionary relationships within the genus. Three age classes of insects (early fourth instar larvae, pupae, and adults) were used. Samples were extracted with acetone and methanol. Following purification, the carotenes and xanthophylls were separated by solvent partitioning and the carotenoids in each fraction were examined by column and thin layer chromatography and by absorption spectrophotometry. The presence of carotenoids was confirmed for five species of Leptinotarsa: L. decemlineata, L. haldemani, L. libatrix, L. rubiginosa, and L. texana. ℬ-carotene was the major carotene present in all species. Lutein and neoxanthin were the major xanthophylls present in L. decemlineata, L. haldemani, L. libatrix, and L. texana. Echinenone and canthaxanthin were the major xanthophylls present in L. rubiginosa, but made up a minor fraction of the xanthophyll concentration in the other four species. ⍺-carotene was a minor pigment of L. decemlineata, L. haldemani, and L. rubiginosa. Astaxanthin was present in L. decemlineata and L. rubiginosa. The concentrations of carotenoids in Leptinotarsa ranged from a low of about 10 µg/g fresh weight in larvae of L. haldemani and L. texana to a high of about 100 µg/g fresh weight in pupae and adults of L. decemlineata. Concentrations of a-carotene ranged from 2 µg/g in larvae of L. texana to 85 µg/g in adult L. decemlineata. Lutein and neoxanthin had concentrations ranging from trace amounts in some samples to about 12 µg/g in larvae of L. decemlineata. Other carotenoids were present in lower concentrations. Four species of host plants were examined: Solanum tuberosum, S. dulcamara, S. elaeagnifolium, and Hyoscyamus niger. They contained ⍺-carotene, ℬ-carotene, lutein, and neoxanthin as did Leptinotarsa, but did not contain detectable quantities of the three keto-carotenoids (echinenone, canthaxanthin, and astaxanthin) which were found in Leptinotarsa. L. decemlineata and L. rubiginosa were characterized as aposematic species and had carotenoid concentrations greater than that of their host plants. The three cryptic species, L. haldemani, L libatrix, and L. texana, had carotenoid concentrations lower than those of their host plants. These relationships held even when the two groups were reared on the same host plant. Aposematic species had high carotene to xanthophyll ratios, whereas the cryptic species had lower ratios similar to those found in the host plants. The significance of these findings is discussed and a model is proposed to explain the evolutionary development of high carotenoid concentrations in Leptinotarsa.

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