Sesquiterpenes behavior

The scent scales on the wings of a male lycaenid, Lycaeides argyroqnomon, secrete a mixture of n-nonanal, hexadecyl acetate, and a sesquiterpene alcohol, tentatively identified as torreyol (5-cadinol) (XXVIII) (113) the absolute configuration of the sesquiterpene has not been determined. These male-derived pheromones appear to play an important role in the courtship behavior of this species. 

Behavioral and sensory disturbance. Potato glandular trichomes, in addition to acting as a physical barrier to pests, manufacture and/or store a profusion of plant metabolic products, some of which profoundly influence insect behavior and metabolism (19,20). The sesquiterpene components of potato trichome glands (21,22,23) are potentially powerful semiochemicals and one of these, E-6-farnesene, is well known for its ability to initiate evasive behavior in aphids (24). The dramatic alteration of aphid feeding behavior on S. berthaultii reported by Lapointe and Tingey (25) may be due to allomonal sesquiterpenes in trichome exudate and will be discussed later. 

The effects of sesquiterpene mixtures from leaf extracts of wild and cultivated potatoes on the settling behavior of green peach aphid were studied in dual-choice assays (22). The sesquiterpene fraction of JS. berthaultii had a strong repellent effect on aphid behavior. Due to use of the slow release medium Carboset, this effect was still apparent beyond six hours. The sesquiterpenoid fraction from cv. Chippewa leaves also strongly repelled aphids. The major foliar sesquiterpene in all extracts, B-caryophyllene, had no adverse effect on settling behavior. 

Table 7. Myzus persicae settling behavior inhibition (%SI) caused by the monoterpene 2,10-bisaboladien-l-one (23) in choice assays. Effective doses (EC50) and geraniol (G), the sesquiterpene precursor farnesol (F) and the sesquiterpene 95% confidence limits (lower and upper) of the test compounds [34].

The toxicity of compounds 27-31 on L. decemlineata was inversely correlated to their antifeedant effects and directly related to their polarity, suggesting a different mode of action or receptor affinity at the central nervous system [20], A similar correlation has been shown between antifeedant effects, toxicity and polarity of structurally-related silphinene sesquiterpenes on CPB and Diabrotica virgifera virgifera [19, 36]. Such a lack of behavioral and toxicity relationship has been noted for a broad selection of plant allelochemicals [43-46]. 

Herbivores can typically sense suitable host plants using olfactory cues from long distance. Many volatile terpenoids bear the essential information in their molecular structure. Different stereo isomers of the same compound may result in different response when sensed by insect antennae or the olfactory sensors in the nose of vertebrate animals. Another important factor affecting signal perception and behavioral response in herbivore is the relative proportion of different volatile compounds, terpenoids or other volatiles, in the odor plume released by a plant. CombinatiOTi of certain monoterpenes and sesquiterpenes are very distinctive in certain plant families. Specialist herbivore species can separate these combinations from similar monoterpenes released by other plants, because of their strict ratio in the host species. 

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