| Abstract | Insects, being highly affected by chemical signals, may be expected to be influenced strongly in their choice of individual host plants by phenotypic differences of volatile compounds stored and released by the plant. (Dethier, 1970). Having gained experience especially in the volatile oil compositions of conifers, I wi11 restrict this discussion to those volatile conifer components that could influence host choice by insects through their olfactory reactions. Although there are some reports in the literature (see review by Hanover, 1975) that implicate several terpenes found in conifer foliage with host-insect interactions, good correlation between terpene composition and either insect attraction or repellancy appears to be lacking. In part this may be due to the complexity o'f the volatile oils found in conifer foliage (von Rudloff, 1975a). Another reason could be that the actual terpene compositon at the time of host-insect interaction has not been examined. Thus, in addition to considerations of the behavioral aspects of e.g. phytophagous insects (Dethier 1953 & 1970, Schoonhoven 1978), or physiological reactions of the insect to the host's chemicals (Schoonhoven 1978, Simpson 1976), the inherent and the seasonal variation in the volatile oil compositon must be taken into account. To complicate matters, the chirality of the terpenes and synergism with insect pheromones must be considered as well (Wood 1973, Silverstein and Young 1976, Vite et al. 1978). |
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