Response of the shot-hole borer of tea, Xyleborus fornicatus (Coleoptera: Scolytidae) to conspecifics and plant semiochemicals

Abstract

The responses of the tea shot-hole borer beetle, Xyleborus fornicatus, to conspecific and host plant odours were tested in an olfactometer. Males showed greater attraction to unmated females than to mated females and mated females showed a negative density dependent response with extremely significant repulsion shown when 10 mated females were present. Plants of the susceptible tea cultivar TRI2025 were significantly more attractive to females than those of the less susceptible cultivar TRI2023, although stem extracts of the susceptible cultivar were not found to be attractive to beetles. Beetles were found to be attracted to ethanol and to the known tea volatiles eugenol, hexanol, α- and β-pinene, geraniol, and methyl salicylate. The attraction of the tea volatiles was found to be enhanced when they were mixed with ethanol, indicating that ethanol has a broad synergistic effect. In a study on phagostimulant effects of tea extracts, sugars, and caffeine, the methanol extract of cultivar TRI2025 and the sugars glucose and sucrose were found to be attractive, and caffeine repulsive, to beetles. Pellets containing the extract were found to be preferred over those containing glucose. Beetles were attracted to pellets containing glucose/inositol mixture with glucose:inositol in the 3:1 ratio found in the susceptible cultivar TRI2025, being preferred to the mixture in 5:1 ratio found in stems of the less susceptible cultivar TRI2025. Both volatile and nonvolatile constituents of tea appear to play a role in attracting the female beetle to the plant.