Graduate Thesis Or Dissertation
 

Seasonal abundance, distribution, and migration of the clover aphid, Nearctaphis bakeri (Cowen) in red clover

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  • Four sampling techniques were evaluated to estimate clover aphid, Nearctaphis bakeri (Cowen), abundance in red clover fields in the Willamette Valley. The Berlese funnel method detected one to four times more aphids than other sampling techniques. Visual assessment often underestimated the high aphid densities during the flowering and seeding of clover. Sweep net and Schuh shaker techniques had limitations and underrated the numbers of aphids present in the clover fields. Strong correlations (r² = 0. 74 - 0.87) were found between the Berlese funnel technique and visual assessment technique in a 2nd year established field. Numerical differences in the spatial distribution of N. bakeri on clover stems were shown during various stages of plant development over the season. During development of buds and axils, aphid numbers on the lower half of the plant averaged 1.5 times greater than those on the upper half. As the season progressed into the flowering and seeding stage, aphid numbers on the upper stem halves were approximately five times greater than those on the lower half. Winged clover aphids were too few to show definite peaks of flight using water traps, averaging 2.19 aphids per yellow bucket during the June-August period. No significant differences in aphid attractiveness to the different colors were found among water pan traps. Yellow buckets captured approximately five times more alate aphids than did yellow, red, or green pan traps. Traps placed on the south side of the field contained higher numbers of aphids than in other locations in the red clover fields.
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