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Articles by Vijaya Kumar
Total Records ( 2 ) for Vijaya Kumar
  W. Subodhi Karunaratne , Vijaya Kumar , Jan Pettersson and N. Savitri Kumar
  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.
  W. Subodhi Karunaratne , Vijaya Kumar , Jan Pettersson and N. Savitri Kumar
  The two tea plant cultivars TRI2023 and TRI2025 are known to show different susceptibilities for attack by the shot-hole borer beetle, Xyleborus fornicatus Eichh. (Coleoptera:Scolytidae). Olfactometric studies showed that female beetles were attracted to both tea cultivars TRI2023 and TRI2025 but preferred the susceptible cultivar TRI2025 to the resistant cultivar TRI2023. In a no-choice experiment where the settlement of beetles on twigs of both cultivars was studied, it was found that in the first hour of attack a greater number of beetles attacked twigs of the resistant cultivar TRI2023 than twigs of the susceptible cultivar TRI 2025. However, after the first hour the rate of attack was inverted, i.e. the established view on the resistance of the two clones was registered in terms of attacks. When twigs had been exposed to beetles for 24 h before attack by a fresh set of beetles, a lesser number of beetles attacked the already infested stems of both cultivars consistently throughout the period of observation compared with attack on healthy stems. The possibility of an induced resistance stimulated by the initial beetle attack is suggested and is hypothetically discussed in terms of a plant-resistance strategy based on using a strong initial attack of beetles as a releaser for induced effects which counteract further attacks.
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