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MANIPULATION OF ACYRTHOSIPHON PISUM (HARRIS) POPULATIONS TO DETERMINE ECONOMIC THRESHOLDS ON ALFALFA IN NEBRASKA
Abstract
To insure a large number of Pea Aphids (PA) Acyrthosiphon pisum (Harris) in the field, cages and methoxychlor (.56 kg/ha) a selective insecticide were utilized to eliminate predators allowing PA populations to build. PA infested cages were compared to check cages treated with carbofuran at .56 kg/ha, to determine the economic threshold of PA for Nebraska conditions. Greatest losses in forage yield (995.3 kg/ha) and protein (201.7 kg/ha) occurred during the August, 1980, harvest on the caged 'Vernal' that accumulated 708 PA days/stem. The monetary loss resulting from the accumulation of 708 PA days/stem was approximately $98/ha. Pea aphid populations must be > 212 PA days/stem before the cost of insecticidal control results in a profit. A study was initiated to determine if there was any effect of the August, 1980 PA infestation on winter survival by calculating the percent stand for two dates--September 17, 1980, and March 31, 1981. Root samples were also taken to determine if the PA infestation interfered with storage of nitrogen and total-non-structural carbohydrates (TNC). Percent stand for PA resistant Baker did not differ between sampling dates. There were significant stand differences in PA susceptible Vernal for both dates. A total reduction of 10.9% occurred on the plots that accumulated 1219 PA days/stem. Analysis of the root samples indicated no significant difference in root storage of either nitrogen or TNC in either the Baker or Vernal plots. Temperature effects on the plant (cultivars), the pest (PA), and beneficial insects (lady beetles) were studied to determine if the temperature during the growing season affected the rate of PA fecundity by favoring any of the biological entities involved. The temperature x variety interaction was significant. PA fecundity decreased with increased temperatures on both cultivars. Beetle consumption of the aphids increased with increased temperature from 32% to 85% of available aphids. This indicates that increasing temperatures during the growing season play in important role in regulating PA populations.
Subject Area
Entomology
Recommended Citation
KARNER, MILES ALLEN, "MANIPULATION OF ACYRTHOSIPHON PISUM (HARRIS) POPULATIONS TO DETERMINE ECONOMIC THRESHOLDS ON ALFALFA IN NEBRASKA" (1981). ETD collection for University of Nebraska-Lincoln. AAI8208357.
https://digitalcommons.unl.edu/dissertations/AAI8208357