Graduate Thesis Or Dissertation
 

The diel activity cycle of the adult alfalfa weevil, Hypera postica (Guill.), in Oregon

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  • The diel fluctuations in the abundance of alfalfa weevils, as measured by sweeping, were studied during 1972 and 1973 in three of the four major alfalfa growing regions of Oregon. It was found that in all regions studied significantly more new generation adults could be captured after dark than during the day in the summer. This negative reaction to light appeared to approach an inverse linear relationship early in the summer but by the end of July a more or less "all-or-none" negative response was observed. Significant decreases in the numbers of weevils captured were usually noted as the nights progressed. These decreases showed a high positive correlation to decreases in the temperature. Samples in Western Oregon during the fall and spring indicated that overwintering adults lost their negative reaction to light. During this portion of the year temperature seemed to play the dominant role, the greatest numbers being captured at mid-day when the temperatures were near their highest points. Samples taken in the spring in Eastern and Central Oregon indicated that Eastern Oregon weevils behaved in the same way as those in Western Oregon. Central Oregon weevils, though, showed a significant increase in the number captured after dark in the spring. It is hypothesized that this difference in activity may reflect a true biological difference rather than being just an artifact caused by climatic or other unknown factors. No significant difference between the activity of male and female weevils was demonstrated on any date at any location. Finally, although wind velocities were measured, no relationship between them and the numbers of weevils captured could be demonstrated. The probable explanation is the low wind velocities encountered during the course of this investigation.
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