Choice, performance and heritability of performance of specialist and generalist insect herbivores towards cacalol and seneciphylline, two allelochemicals of Adenostyles alpina (Asteraceae)

We compared the effects of a sesquiterpene (ST, cacalol) and a pyrrolizidin e alkaloid (PA, seneciphylline), both occurring in Adenostyles alliariae, o n food choice and performance of specialist and generalist insect herbivore s which are all known to feed or live on A. alliariae. In choice experiment s we investigated whether the compounds were preferred, deterrent or had no effect. All specialist species Aglaostigma discolor (Hymenoptera, Tenthred inidae), Oreina cacaliae (Coleoptera, Chrysomelidae) and O. speciosissima a voided feeding when confronted with the combination of compounds. Only larv ae of A. discolor avoided the single ST treatment as well. Larvae of the ge neralist species Callimorpha dominula (Lepidoptera, Arctiidae), Cylindrotom a distinctissima (Diptera, Tipulidae) and Miramella alpina (Caelifera, Acri didae) generally avoided feeding from PA, ST and PAST treatments. The only exception were caterpillars of C. dominula which were indiscriminate toward s PA when naive, and preferred to feed on the PA treatment when they had ex perienced the compound before. Performance, measured as the growth of larvae on the different treatments i n a no choice situation over a period of 10-17 days, was not different betw een treatments in the specialist leaf beetles O. cacaliae and O. speciosiss ima. 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 C. dominula only the high concentration combination treatme nt (PAST) reduced growth of the larvae due to decreased consumption. In C. distinctissima we found reduced growth in all treatments except one (PA3%). Poor growth performance in C. distinctissima was due to postingestive phys iological effects of all treatments and additionally to consumption reducti on in high-dose ST treatments. Genetic variability (broad sense heritability) of growth performance metabo lism varied in accordance with the specialization degree of the species. O. cacaliae, the most specialized species, had no significant heritability; O . speciosissima, the less specialized specialist, had a heritability of 0.4 6; C. dominula, the PA adapted generalist species, had a heritability of 0. 64; C. distinctissima, the generalist with no apparent adaptations, had a h eritability of 0.84.