Masters Theses

Date of Award

12-1991

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Jerome F. Grant

Committee Members

Charles D. Pless, Gary L. Lentz

Abstract

Helicoverpa zea and Heliothis virescens are important crop pests. Both species are multivoltine and polyphagous enabling them to overlap cropping periods on wild host plants. Several studies of wild and cultivated host plants of Helicoverpa zea and Heliothis virescens have been conducted in the major cotton-growing regions of the southern United States. These studies were conducted to assess the development of an area-wide management strategy for controlling these pests on species of wild hosts.

No comprehensive study of these host plants had been conducted in eastern Tennessee. Therefore, a two-year study was initiated to: 1) determine the complex of wild and cultivated host plants of Helicoverpa zea and Heliothis virescens in this region and 2) to examine host suitability of selected wild host plants in the laboratory.

Helicoverpa zea or Heliothis virescens larvae were collected from 37 species of wild host plants in eleven plant families, which is the second-greatest plant species diversity compared to previous studies. Individually, Helicoverpa zea was collected from 32 plant species in 11 plant families and Heliothis virescens was collected from 21 plant species in eight families. Both Helicoverpa zea and Heliothis virescens were collected from 16 plant species in seven plant families.

Early-season wild host plants considered to be important in other regions of the southern United States (e.g., the Southeast and the Mississippi Delta) were apparently not important in eastern Tennessee, Potentially important early-season host plants in eastern Tennessee included black medic, Medicago lupulina L., for Heliothis virescens, and common mallow and crown vetch for both insect species. Black medic continued to be an important host plant for Heliothis virescens into mid season, and crown vetch was an important host plant in late season for Helicoverpa zea. Other important mid-to late-season wild hosts for both insects were hophornbeam copperleaf, velvetleaf, and tall and ivy-leaved morning glory. Important late-season host plants for Helicoverpa zea were fall panicum, hairy galinsoga, and prickly sida. Of the wild host plants, the greatest number of larvae were collected from prickly sida, Sida spinosa L., where 308 (36% of all Helicoverpa zea collected) Helicoverpa zea larvae were collected.

Laboratory feeding studies indicated that, in late-season, crown vetch and tall morning glory are good nutritional host sources for successful development of Helicoverpa zea while prickly sida may not be as suitable a host. These experiments also indicated that phytochemicals in crown vetch may be toxic to Helicoverpa zea in mid season. Along with mid-season die-back of crown vetch, these phytochemicals may help to reduce populations of this pest on this plant for that time period.

The most important cultivated host plants of Helicoverpa zea and Heliothis virescens were com and tobacco, respectively. Alfalfa was of moderate importance for Helicoverpa zea in late-season. Few larvae were collected from tomato and none from soybean.

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