Effect of temperature and leaf age on growth versus moulting time of a generalist caterpillar fed plantain (Plantago lanceolata) |
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Authors: | NE STAMP MD BOWERS |
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Institution: | Department of Biological Sciences, Binghamton University, State University of New York;University of Colorado Museum and Department of Environmental, Population and Organismic Biology, University of Colorado |
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Abstract: | Abstract. - 1 The simultaneous effects of daytime temperature (20°C versus 30°C) and leaf age (new versus intermediate-aged) on a generalist insect herbivore were examined. Fourth-instar Spilosoma congrua caterpillars were tested on plantain (Plantago lanceolata), one of this lepidopteran species’host plants, for which the major defensive chemicals, iridoid glycosides (aucubin and catalpol), could be quantified.
- 2 Cool temperature depressed amount of food eaten, amount of frass, and consumption and growth rates, and increased the proportion of time spent in the non-feeding period (from head-capsule slippage to ecdysis).
- 3 Average iridoid glycoside concentration was 2.8% dry weight (d.w.) in new leaves and 1.6% d.w. in intermediate-aged leaves. When fed new leaves, the caterpillars had a higher efficiency of conversion of ingested food to biomass and a higher growth rate than those fed intermediate-aged leaves. Furthermore, the proportion of time spent in the non-feeding period was prolonged by a diet of intermediate-aged leaves.
- 4 A second experiment showed that the percentage dry weight of aucubin, catalpol and total iridoid glycosides increased over 24 h in incubated, excised leaves, which meant that the caterpillars in the first experiment experienced somewhat higher iridoid glycoside concentrations than the levels in fresh leaves.
- 5 Overall, these results indicate that this generalist should prefer new plantain leaves over older leaves even though new leaves contain higher concentrations of iridoid glycosides.
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Keywords: | Iridoid glycoside nutritional ecology Plantago lanceolata Spilosoma congrua temperature |
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