Date of Award

1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

Abstract

Part I of this dissertation involved the use of the biological insecticides Dipel('(REGTM)), Bacillus thuringiensis Berliner, and Elcar('(REGTM)) Baculovirus heliothis for control of Heliothis spp. on cotton in Louisiana. Seven tests with plots large enough to be considered "grower management units" (plot size 8.1 ha or greater) and one small plot test (plot size 1.3 ha) were conducted using biological insecticides. These tests showed that: (1) generally more Heliothis eggs were found in Dipel treated plots; (2) damage to cotton squares following Dipel applications was generally reduced somewhat; (3) damage to cotton squares following the use of Elcar was not reduced; (4) some reduction in predatory arthropod levels followed the application of both materials; (5) some reduction of tarnished plantbugs, Lygus lineolaris (Palisot de Beauvois), cotton fleahoppers, Pseudatomoscelis seriatus Reuter, and cicadellids followed the use of both materials; (6) yields were not improved following early season use of biological materials; (7) no significant reduction in numbers of insecticide applications were observed; and (8) applications of chemical insecticides for Heliothis control were not observably delayed following early season Heliothis suppression programs using biological insecticides. Part II of this dissertation was a study of the species composition and seasonal distribution of the predatory arthropods commonly found in Louisiana cotton fields. Three distinct cotton growing agro-ecosystems were used as study areas: the Red River Valley, the Macon Ridge and the Mississippi Delta. Predatory arthropod populations were monitored both on plants other than cotton, during times of the year when cotton was not a suitable host, and on untreated cotton plants. The predator groups studied were the coccinellids, Geocoris spp., the nabids, Orius spp. the hemerobiids and chrysopids, and the spiders. This was the first study to describe the species composition of nabid and chrysopid populations associated with cotton agro-ecosystems in Louisiana. In winter, many arthropod predators were found on cool season annual grasses. During spring, increasing numbers of predatory arthropods were found on leguminous plants. In early summer, grain sorghum, Sorghum bicolor (L.), and Johnson grass, Sorghum halepense (L.), were important as reservoirs of several predators. In the fall, high levels of many predatory species were found on alfalfa, Medicago sativa (L.), and grain sorghum. On untreated cotton, predator populations decreased somewhat in early July in all three cotton agro-ecosystems studied. Populations in Red River Valley untreated cotton decreased more than did those in Macon Ridge or Mississippi Delta untreated cotton fields. Also, the Red River Valley predator population was composed of a higher percentage of spiders than were the populations of the Macon Ridge or Mississippi Delta during 1979. An increase in the percentage of spiders in the predator complex may reduce the effectiveness of the predator complex against Heliothis spp. by: (1) spiders taking lower numbers of pest insects than many insects predators; (2) reduced egg predation by predator complexes composed of high percentages of spiders; and (3) predation of spiders on other arthropod predators. It is suggested that the combined effect of decreasing numbers of all arthropod predators and increasing percentages of spiders in the total predator population might be two reasons why the Red River Valley area has experienced traditionally more severe Heliothis problems in cotton.

Pages

181

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