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Journal of Chemical Ecology 22: 1367-1388 (1996)

Combined Chemical Defenxes Against an Insect-Fungal Complex

K D Klepzig , E B Smalley , K F Raffa
ABSTRACT
This study considered how host plant allelochemicals may contribute to defense against insects and fungi that jointly colonize the subcortical tissues of trees, the relative roles of constituitive and inducible chemistry in these defenses, and how the actions of two different feeding guilds might be interrelated. Our model consisted of the coniferous tree {IPinus resinosa}, the root-and lower stem-colonizing beetles {IHylastes porculus} and {IDendroctonus valens}, and their associated fungi {ILeptographium procerum} and {IL. terebrantis}, and the stem-colonizing bark beetle {IIps pini} and its associated fungus {IOphiostoma ips}. In a novel bioassay, extracts from reaction tissue elicted by wound inoculation with {IL. terebrantis} were more repellent to beetles than were similar extracts from constitutive or mechanically wounded tissue. The effect on beetle behavior was more pronounce in nonpolar extracts, which contain mostly monoterpenes, than in polar extracts, which contain mostly phenolica. Synthetic monoterpenes at concentrations present in the various tissues exerted similar effects and were likewise repellent in dose-response experiments. Growth of {IL. procerum} and {IL. terebrantis} was inhibited by polar extracts from constitutive and reaction tissue. Inhibition was higher in wounded than control tissue, but the inhibition response did not vary with the type of wounding. Synthetic monoterpenes strongly inhibited spore germination and mycelial growth of both fungi. Colonization of red pine roots by {ILeptographium} spp. altered the subsequent effects of extracts of stem phloem tissue on {II. pini}. These effects varied with host condition. Bettles preffered extracts from constitutive stem phloem tissue of healthy trees to that of root-diseased trees. However, extracts from reaction tissues of healthy trees were more repellent to {II. pimi} than were the reaction tissues of root-diseased trees. The implications of these results to plant defense agains insect-fungal complexes and interactions among different feeding guilds are discussed.
Notes
Combined Chemical Defenxes Against an Insect-Fungal Complex1139