Graves, Sarah Rachael; (2003) The role of component ratio integrity in host-plant selection: A chemical and biological approach. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The role of ratio integrity between volatile semiochemicals (behaviour modifying chemicals) in host-plant selection was investigated using the pea and bean weevil, Sitona lineatus L., as the model insect. The quantification of the attraction of S. lineatus to traps baited with modified ratios of host (Vicia faba) semiochemicals together with synthetic aggregation pheromone was evaluated statistically. The bait mixture contained (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, l-octen-3-ol, 2- phenylethanol, beta-caryophyllene, benzyl alcohol, alpha-terpineol, hexanal, linalool plus the pheromone, 4-methyl 3,5-heptanedione. The results of a physico-chemical properties study were exploited to develop a stable release medium for semiochemicals of S. lineatus. In particular, the Abraham general solvation equation was used to model the transfer properties involved in the evaporation of a compound from a glass vial. A multiple linear regression analysis was performed between the Abraham descriptors and the rate constant for the loss of compound from a glass vial. Though, no utilizable correlation was found. The performance of the glass vial release medium developed was compared to a polythene closure ("Polybag") system. S. lineatus were not significantly attracted to the 9 compound bait mixture in the absence of the aggregation pheromone. When the ratio of (Z)-3-hexenyl acetate to (Z)-3-hexen-1-ol was modified in favour of (Z)-3-hexenyl acetate, the baits became less attractive to S. lineatus. Other minor modifications of the bait mixture were also tested but found not to decrease the attractiveness of the mixture. The results suggest, and support, the idea that host-plant selection involves the detection of ubiquitous compounds and it is the ratios of the key components that are required for specificity.

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