Factors Influencing the Orientation and Rates of Activity ofDendroctonus ponderosaeHopkins (Coleoptera: Scolytidae)

Abstract

The tactic and kinetic responses of adultDendroctonus ponderosaeHopkins were studied under varying conditions of light, temperature, humidity, gravity, and with different visual forms. Newly emerged adultDendroctonus ponderosaeHopk. were attracted by high light intensity and utilized spot sources of light and surrounding objects, but not polarized light, for orientation. Flying adults were positively phototactic unless warmed above 35 °C; egg-laying adults were negatively phototactic. High temperatures and light intensities increased the frequency of flights. The beetles were negatively geotropic but this could be masked by the attraction to light. Dark objects on a light background were attractive; the size of the object was important while the shape was not.Temperature influenced orientation to some extent but its influence on rate of activity was far more pronounced; rate of walk followed a linear relationship with temperature. Humidity also affected orientation and rate of walk to some extent, although its effect was usually masked by other environmental factors.