Relative Expression of Crystalline Proteins among the Fruiting Structures of Transgenic Cotton Over Time and Its Impact on Bollworm Mortality

Authors: Little, Nathan; Paulk, Ryan; Elkins, Blake; Allen, Clint

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2024
Publication Date: 6/17/2024
Citation: Little, N., Paulk, R.T., Elkins, B.H., Allen, K.C. 2024. Relative Expression of Crystalline Proteins among the Fruiting Structures of Transgenic Cotton Over Time and Its Impact on Bollworm Mortality. Southwestern Entomologist. 49(2):1-14. https://doi.org/10.3958/059.049.0215.
DOI: https://doi.org/10.3958/059.049.0215

Interpretive Summary: The bollworm is a major economic insect pest of cotton in the U.S. Transgenic cottons that express multiple insecticidal proteins throughout the plant are the primary means of control for this pest. However, the insect must ingest the protein while feeding on the cotton plant for it to cause mortality. In this study, we quantified two insecticidal proteins in three different fruiting forms of a widely used dual-gene cotton in the U.S. and related it to larval mortality that resulted from feeding on these structures. To accomplish this, we used a novel technique to indirectly quantify insecticidal proteins based on relative quantities. We found that larval mortality was highly related to relative protein concentrations. However, not all of the mortality could be attributed to the presence of the proteins. A larger proportion of bollworm larvae that were fed cotton squares died relative to that observed for blooms and bolls, regardless of protein levels in the structures. This study will serve as a framework for assessing the insecticidal protein contribution of newer triple-gene cottons on bollworm larval mortality in the field.

Technical Abstract: The inherent insect protection provided by transgenic cotton [Gossypium hirsutum L. (Malvaceae)] has played an appreciable role in profitable cotton production in the U.S. Understanding the effects of variable crystalline protein expression in fruiting structures of dual-gene transgenic cotton on bollworm [Helicoverpa zea Boddie (Noctuidae)] larval survival is important to managing the development of insect resistance. Enzyme-linked immunosorbent assays were used to evaluate the relative expression of two crystalline proteins (Cry1Ac and Cry2Ab) present in squares, blooms, and bolls of a Bollgard II cotton variety over time. We assessed the effects of these proteins using third instar larvae from a susceptible colony of bollworms in laboratory bioassays on the respective plant tissues. Both crystalline proteins were positively correlated with bollworm larval mortality and negatively correlated with larval penetration across all fruiting structures of Bollgard II cotton. Bollworm larval mortality was higher in squares (48.89% ± 4.16) of Bollgard II cotton than in bolls (20.00% ± 2.66) or blooms (13.33% ± 1.93). Bollworm larval penetration of fruiting structures was lower in Bollgard II (42.47% ± 4.59) than non-Bt cotton (75.1% ± 4.76). In Bollgard II cotton, larval penetration was highest in squares (77.78% ± 5.76), followed by bolls (62.6% ± 4.83), and then flowers (35.93% ± 6.15). Our findings indicate that optical density was effective for assessing the effects of protein expression on bollworm larval mortality in various cotton fruiting structures of a Bollgard II cotton variety. Techniques from this study can be used to understand the contribution of Vip3A to bollworm larval mortality in newer, third-generation transgenic cottons recently released in the U.S.