Nathan Egan Rank

Rank, N. E. 1992. Host plant preference based on salicylate chemistry in a willow leaf beetle (Chrysomela aeneicollis). Oecologia 90: 95-101.

Chrysomela aeneicollis (Coleoptera: Chrysomelidae) uses salicin from its host plant (Salix spp.) to produce a defensive secretion, salicylaldehyde. Because it requires salicin for this defensive secretion, I predicted that C. aeneicollis should be attracted to willows which possess salicin and other salicylates. To test this prediction, I determined the host-plant preferences of C. aeneicollis among four willow species which have very different salicylate chemistries and which are common in the beetle's natural habitats in the Sierra Nevada range of eastern California. In oviposition-preference tests, gravid females showed no preference between a salicylate-poor species, S. lutea, and a salicylate-rich species, S. orestera. However in feeding-choice tests, both larvae and adults preferred S. orestera over S. lutea. This preference was not affected by the species on which the larvae were reared. Other feeding tests showed that adults which I had collected on S. orestera and two medium-salicylate species, S. boothi and S. geyeriana, all preferred S. orestera, regardless of which host species they had been collected on. In a final feeding test, adults were stimulated to feed by salicin itself. On the same four willow species in nature, the relative abundances of C. aeneicollis adults and egg clutches correspond to the feeding preference in the laboratory. Additionally in multiple regression analyses, adult abundance was not related to among-clone differences in leaf toughness or nutritive quality, but rather to plant size and salicin content. Thus for C. aeneicollis, both laboratory and field results demonstrate a preference for salicylate-rich willows which appears to lead to the increased level of attack on them.

Key words: Chrysomelidae - Salix - salicin - herbivore feeding preference - host-plant choice

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November 8, 1997 NER