Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

Abstract

Experiments conducted in soybean, Glycine max (L.) Merrill, fields in 1983 and 1984 demonstrated that damage by both adults and nymphs of the second generation of the threecornered alfalfa hopper, Spissistilus festinus (Say), on soybean (third generation of the year) contribute to yield reduction. Results indicated nymphs were responsible for 45-60% of the total yield reduction. The vertical beat sheet, ground cloth, and beat net techniques for sampling S. festinus nymphs were evaluated in soybean fields utilizing systematic and random sampling. Based on the proportion of the population sampled, the relative variation, and regression on subsequent adult counts, the best net and ground cloth techniques were determined to be best for sampling S. festinus nymphs. Field surveys indicated no localization of populations within a field; therefore, random sampling across a field was determined to be sufficient to sample S. festinus populations. Distributional analyses indicated nymphs to be clumped when sampled with the ground cloth or vertical beat sheet. Beat net sampling indicated nymphs were clumped early in the season; however, nymphal distribution fit a poisson (random) distribution during the second generation on soybean. Distribution of adults appeared clumped at the beginning of each generation's adult emergence but were generally random on subsequent sample dates within a generation. Thresholds for numphs sampled with the beat net and ground cloth techniques were established using regression analyses of nymphs on adults and solving the equations for the known adult threshold (one per sweep). Sequential sampling plans were developed for S. festinus adults sampled with the sweep net and for nymphs sampled with the beat net and ground cloth techniques. Field insecticide efficacy studies for S. festinus control demonstrated the added capability of interpreting results if the nymphal population is sampled. Of nine insecticides evaluated, three pyrethroids (cyhalothrin, 0.0336 kg AI/ha; fenvalerate, 0.084 and 0.112 kg AI/ha; and cyfluthrin 0.014 and 0.028 kg AI/ha) and an insect growth regulator (buprofezin, 0.37 and 0.56 kg AI/ha) were found to provide the best control. Buprofezin provided the longest residual activity with control of early instars indicated at 15 days posttreatment.

Pages

93

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