Factors Influencing Sweep-Net Sampling of Alfalfa1

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Abstract
Sweep-net counts were made on 3 species of insects (pea aphid, Acyrthosiphon possum (Harris); potato leafhopper, Empoasca fabae (Harris); and meadow spittle bug, Filaments summaries (L.)) in alfalfa near Lafayette, Indiana. Sweeps were taken at 0800, 1200, and 1600 hrs CDT every Monday from June 22 to September 7, 1964 by 2 individuals using 2 types of nets and 2 sampling plans. Weather data from Pursue University Airport were used in analyzing the counts. The counts were analyzed by a complete 5-factor factorial experiment and a multiple regression model with 16 independent variables. Factorial analyses indicated that when the counts for the 3 species were relatively high, most main effects and 2 factor interactions were significant with higher-order interactions generally non significant. However, when the counts were low for pea aphids and potato leafhopper’s, many higher-order interactions were also significant. The multiple regression analyses found all 16 independent variables included to influence significantly the counts of at least I of the 3 species studied. Height of alfalfa and weeks were the most important variables for pea aphids and potato leafhoppers, whereas temperature and relative humidity appeared to be the most important for meadow spittle-bugs. The degree of variability of insect counts found in this study would indicate that the precision of sweep-nets may not be sufficient to make critical population comparisons, but they can be used to determine major population trends.

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