Masters Theses

Date of Award

8-1989

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Jerome F. Grant

Committee Members

Charles Pless, Robert Miller

Abstract

Alternative insect pest management tactics, such as host plant resistance and biological control, have recently received more research emphasis due to the current concern over pesticide residue and contamination problems. In addition, several insect species have been shown to be resistant to several commonly used pesticides, which poses a problem in control of these pest species. Little information is available on the influence of breeding lines/cultivars of tobacco on populations of Heliothis species, as well as on their larval parasitoid species. Therefore, a two-year study was initiated to better understand this host plant-pest-natural enemy interaction. The objectives of this study were to: 1) determine the species composition and seasonal incidence of Heliothis on tobacco, 2) determine the seasonal parasitism levels and species composition of larval parasitoids on tobacco, 3) evaluate the influence of selected tobacco breeding lines/cultivars on populations of Heliothis, and 4) evaluate the influence of selected tobacco breeding lines/cultivars on populations of parasitoids of larvae of Heliothis. As many as three generations of Heliothis larvae may have occurred on tobacco, with Heliothis virescens, the tobacco budworm, comprising ca. 83% of the Heliothis spp. collected. Heliothis zea, the corn earworm, comprised the remaining 17% of the Heliothis larvae collected from tobacco. Campoletis sonorensis, Cardiochiles nigriceps, Microplitis croceipes, Archytas marmoratus and other tachinid species (possibly all Winthemia rufopicta) were found to parasitize ca. 25% of the Heliothis larvae collected from tobacco in eastern Tennessee. Campoletis sonorensis, present throughout the entire tobacco-growing season, was the most important parasitoid species, accounting for ca. 90% of all parasitism. In 1987, Archytas marmoratus and several other tachinid species were present late in the season and accounted for ca. 5% of the total parasitism of Heliothis larvae. In 1988, however, tachinid species accounted for ca. 0.3% of the parasitoid complex. Populations of Heliothis larvae were influenced by the duvane diterpenes secreted from the leaf surfaces of selected breeding lines/cultivars of tobacco. Those breeding lines/cultivars that secreted high levels of duvane diterpenes also had high levels of Heliothis larvae. Early (mid-June to late July) in the tobacco-growing season, densities of Heliothis larvae were ca. three times (Knoxville, 1988) to ca. six times (Knoxville, 1987) greater on the tobaccos that secreted high levels of duvane diterpenes ("sticky") than on those that secreted low levels of duvane diterpenes ( "non-sticky" ). In general, parasitism levels were lower on the "non-sticky" (especially TI 1112) lines than on the "sticky" lines of tobacco.

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