Choice, performance and heritability of performance of specialist and generalist insect herbivores towards cacalol and seneciphylline, two allelochemicals of <i>Adenostyles alpina</i> (Asteraceae)
Hägele, Bernd F.
Date de parution
Journal of Evolutionary Biology, Wiley, 2001/13/1/131-142
We compared the effects of a sesquiterpene (ST, cacalol) and a pyrrolizidine alkaloid (PA, seneciphylline), both occurring in <i>Adenostyles alliariae</i>, on food choice and performance of specialist and generalist insect herbivores which are all known to feed or live on <i>A. alliariae</i>. In choice experiments we investigated whether the compounds were preferred, deterrent or had no effect. All specialist species <i>Aglaostigma discolor</i> (Hymenoptera, Tenthredinidae), <i>Oreina cacaliae</i> (Coleoptera, Chrysomelidae) and <i>O. speciosissima</i> avoided feeding when confronted with the combination of compounds. Only larvae of <i>A. discolor</i> avoided the single ST treatment as well. Larvae of the generalist species <i>Callimorpha dominula</i> (Lepidoptera, Arctiidae), <i>Cylindrotoma distinctissima</i> (Diptera, Tipulidae) and <i>Miramella alpina</i> (Caelifera, Acrididae) generally avoided feeding from PA, ST and PAST treatments. The only exception were caterpillars of C. dominula which were indiscriminate towards PA when naive, and preferred to feed on the PA treatment when they had experienced the compound before. <br> Performance, measured as the growth of larvae on the different treatments in a no choice situation over a period of 10–17 days, was not different between treatments in the specialist leaf beetles <i>O. cacaliae</i> and <i>O. speciosissima</i>. Their avoidance of the combination treatment in the choice experiments had no obvious effect on growth when forced to feed from the treatment. In the generalist <i>C. dominula</i> only the high concentration combination treatment (PAST) reduced growth of the larvae due to decreased consumption. In <i>C. distinctissima</i> we found reduced growth in all treatments except one (PA3%). Poor growth performance in <i>C. distinctissima</i> was due to postingestive physiological effects of all treatments and additionally to consumption reduction in high-dose ST treatments. <br> Genetic variability (broad sense heritability) of growth performance metabolism varied in accordance with the specialization degree of the species. <i>O. cacaliae</i>, the most specialized species, had no significant heritability; <i>O. speciosissima</i>, the less specialized specialist, had a heritability of 0.46; <i>C. dominula</i>, the PA adapted generalist species, had a heritability of 0.64; <i>C. distinctissima</i>, the generalist with no apparent adaptations, had a heritability of 0.84.
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