Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

Document Type



The ecology of bollworms, Helicoverpa zea (Boddie), on Bollgard and Bollgard II cottons, Gossypium hirsutum L., was studied in field and laboratory experiments. Neonate bollworm larvae were placed on selected components of cotton squares and flowers from non-Bollgard, Bollgard, and Bollgard II cotton varieties. Larval survival was higher on flower anthers and square anthers than on other floral parts for each cultivar. Bollworm survival was lowest on all Bollgard II floral structures. To evaluate larval behavior on Bollgard cotton, first instar bollworms were placed on terminals of non-flowering and flowering cotton plants. Larvae were recovered lower on Bollgard cotton than on non-Bollgard cotton. Larvae remained near the terminals of non-Bollgard plants feeding on terminal foliage and squares. On Bollgard cotton, more larvae were recovered from white flowers and bolls. To quantify injury from bollworms on Bollgard and Bollgard II cottons, first instar larvae were placed in white flowers of non-Bollgard, Bollgard, and Bollgard II cottons. Bollworms damaged approximately two and three times more fruiting forms on non-Bollgard cotton than on Bollgard and Bollgard II cottons, respectively. To evaluate the influence of alternate hosts on bollworm sensitivity to non-Bollgard and Bollgard cottons, host colonies were established on field corn, Zea mays L.; grain sorghum, Sorghum bicolor (Moench); soybean, Glycine max (Merrill); non-Bollgard cotton; and meridic diet. Field corn and grain sorghum were better hosts for bollworms than cotton. Neonates from each colony were placed on terminal foliage from non-Bollgard and Bollgard cottons in petri dishes. Mortality of larvae from the cotton colony was higher than mortality from the soybean, corn, and meridic diet colonies on non-Bollgard cotton. Mortality from the corn colony was higher than from the soybean and grain sorghum colonies on Bollgard cotton. Differences in bollworm larval behavior and development on Bollgard cotton suggest that changes are needed in the scouting protocols and management decisions for bollworms on Bollgard cotton compared to those on non-Bollgard cotton. Insecticide applications will be needed for bollworms on Bollgard cotton when populations persist over extended periods of time or when other boll feeding pests are present. Furthermore, alternate hosts may influence bollworm management with Bollgard cotton.



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Committee Chair

Roger Leonard