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A study of some factors influencing the orientation behaviour of the ambrosia bettle Trypodendron lineatum (Olivier) (Coleoptera : Scolytidae) Chan, Vernon Bruce

Abstract

The behaviour of the ambrosia beetle Trypodendron llneatum (Olivier) has been considered in respect to illumination, body moisture and host factors. The investigation was designed to study potential uses of this insect as a test instrument for chemical studies of host wood attractants. A preliminary study of host attractants was also conducted using a newly-proposed bioassay technique. Monochromatic light at the wavelength 543 millimicrons was found to be the sole peak of stimulation to this insect in the visible spectrum. Beetles displayed a positive photic response by walking toward the source of light. A decrease in sensitivity occurred on either side of this peak, and in the longer wavelengths the sensitivity to light diminished at 735 millimicrons. Evidence to date indicated a second peak of sensitivity in the ultraviolet region of the spectrum; the latter appearing to be much greater than the peak in the visible spectrum. The intensity of any wavelength was also found to be a limiting factor in affecting beetle response, although in the longer wavelengths the sensitivity appeared to be a function of wavelength alone. Monochromatic light as a standard has been proposed for future bioassay techniques to act in opposition to odour stimuli. Red illumination was found to be effective in simulating darkness to T. lineatum. ‘Green’ unattractive sapwood shavings of Douglas-fir after placement under oxygen deficient conditions became attractive to T. lineatum. Maximum attractiveness was indicated in wood placed under anaerobiosis for 20 to 26 hours. Beyond 30 hours, little sign of attractants was noted. Control wood series did not undergo any transition, this leading to the conclusion that a significant change occurred in wood as a result of the anaerobic treatment. The implications of this result have been discussed. The successful use of wood shavings has made possible further studies on the nature of origin of attractants. The use of the anemotactic behaviour of beetles of both sexes to an airstream carrying host odour was found to be a highly efficient technique of analysis. The role of greater quantities of light in attracting insects away from a source of olfactory stimulation became increasingly apparent from this study. Moisture loss of the insect apparently did not alter their response to white light.

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