Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

David J. Boethel

Abstract

In a laboratory experiment with five genotypes of soybean, Glycine max (L.) Merrill, developmental time and fecundity of Tetranychus urticae Koch was measured. Developmental time for virgin females on leaf disks was shortest on Plant Introduction (PI) 227687, 'DSR 352,' and 'Williams.' There were no differences in development time for male mites due to genotype. Females laid more eggs per day on PI 227687 and more total eggs on PI 227687 and 'DSR 352' than on 'Williams,' 'Clark,' and 'Davis.' Life tables were constructed for mite cohorts on each soybean genotype. Values for r, intrinsic rate of increase, ranged from 0.26018 on 'Davis' to 0.32402 on PI 227687. A positive correlation between the period of peak egg production and the intrinsic rate of increase suggested a rapid technique for screening plants for resistance to spider mites. Further laboratory experiments were conducted with nine genotypes of soybean to measure their effect on fecundity of T. urticae during peak egg production period of 5 days. Fecundity in both virgin and mated females was significantly affected by soybean genotypes and by the mites' mating status. The cultivar 'Tracy M' demonstrated antibiosis to T. urticae by reducing egg production. PI 227687, which has demonstrated resistance to soybean insects, and 'DSR 352' were the most susceptible genotypes. Mated females laid more eggs than virgin females. Hatchability of the eggs was not affected by soybean genotype or mating status. Populations of a predaceous mite, Phytoseiulus persimilis Athias-Henriot, and its prey, T. urticae, were examined on a resistant and a susceptible soybean genotype that had been identified in the earlier studies. Both predation and the resistant soybean genotype reduced the phytophagous mite population, with the predation effect being the more pronounced. When adequate prey were available, there was no indication of antibiosis effects on the predator's population from feeding on prey reared on resistant host plant material. The P. persimilis population was reduced only at the lowest prey density examined, due to lack of prey and subsequent cannibalism.

Pages

117

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