FOOD WEB RELATIONSHIPS OF GEOCORIS PALLENS STAL AND ORIUS TRISTICOLOR (WHITE) ON COTTON PLANTS. PART I. A COMPARISON OF THREE METHODS FOR DETERMINING ARTHROPOD POPULATION NUMBERS ON COTTON. PART II. ARTHROPODS ON COTTON PLANTS: SEASONAL AND VERTICAL DIST

This dissertation consists of three studies of arthropod pest-prey relationships on cotton in the San Joaquin Valley of California. The three studies are written separately in manuscript style for publication.; Part I. Major and secondary pest and beneficial arthropod populations were sampled in San Joaquin Valley cotton fields in California. Three methods were compared as measures of arthropod numbers: a visual examination of cotton plants, a modified berlese funnel method, and whole plants collected in cloth bags. Numbers of the several arthropods collected by the three methods are compared with developmental stages separated where possible. No significant differences in the numbers collected by the three methods were detected when arthropod populations were at low densities. No single method was most effective for estimating all life stages of any particular arthropod species. A combination of the bag and berlese funnel methods provided a better estimate for some arthropod populations than the use of bags alone. These methods are suitable for research purposes, but not for scouting programs.; Part II. Seasonal and vertical distribution of arthropods on cotton plants was evaluated by visual inspection of the whole plants in the field. Most arthropods species gradually increased in population density from early to late season and reached highest values on the last week of August about the time of cotton maturity. Beginning in early September most populations drastically decreased. Geocoris pallens Stal decreased about mid-August and mites and thrips continued increasing after August 29. Highly significant regressions were calculated between number of arthropods located on progressively higher main stem nodes and the increase in height of the cotton plant. A majority of the arthropods were found in the upper third of the cotton plant throughout the cotton growing season.; Part III. Western flower thrips, Frankliniella occidentalis (Pergande) and spider mites, Tetranychus pacificus McGregor, are common elements of the cotton field phytophagous fauna. Numerical response and survival was evaluated for the western big-eyed bug Geocoris pallens Stal and the minute pirate bug Orius tristicolor (White) fed on these mites, thrips and on cotton plants. In laboratory and field cage studies increases in numbers of G. pallens were significantly greatest with the pacific spider mite as prey, intermediate with the western flower thrips and lowest when only plants were available. No statistically significant differences at the 5% level were detected in the numerical response of O. tristicolor to the prey provided, although there were consistent patterns of greatest numerical increase with thrips as prey, intermediate with spider mites, and least with the cotton plant as the only source of food.