Sublethal effects of a commercial Bt product and Bt cotton flowers on the bollworm (Helicoverpa zea) with impacts to predation from a lady beetle (Hippodamia convergens)

Authors: Elkins, Blake; Portilla, Maribel; Allen, Clint; Little, Nathan; Mullen, Regina; Paulk, Ryan; Read, Quentin

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2024
Publication Date: 5/6/2024
Citation: Elkins, B.H., Portilla, M., Allen, K.C., Little, N., Mullen, R.M., Paulk, R.T., Read, Q.D. 2024. Sublethal effects of a commercial Bt product and Bt cotton flowers on the bollworm (Helicoverpa zea) with impacts to predation from a lady beetle (Hippodamia convergens). PLOS ONE. 19(5):e0302941. https://doi.org/10.1371/journal.pone.0302941.
DOI: https://doi.org/10.1371/journal.pone.0302941

Interpretive Summary: Bt insecticides used to control pests in cotton are the most important management strategy for the cotton bollworm. However, Bt toxins do not always kill bollworms. We conducted a set of experiments to evaluate bollworm larvae exposed to Bt toxins and how Bt exposure effected predation from a lady beetle natural enemy. Bt exposure was tested by adding Bt toxins to artificial bollworm diet and allowing bollworm larvae to feed on Bt cotton flowers. The results indicated reduced weight and development of bollworms from both methods of Bt exposure. Bt incorporated into artificial diet was found to increase predation from the lady beetle for several days. This effect was only found for larger lady beetle larvae. Results from these experiments show sublethal effects from Bt can alter pest-natural enemy interactions and enhance predation. This is important for understanding the function of biological control in Bt cotton fields.

Technical Abstract: Insecticidal Bacillus thuringiensis Berliner (Bt) toxins produced by transgenic cotton (Gossypium hirsutum L.) plants have become an essential component of cotton pest management. Bt toxins are the primary management tool in Bt cotton for lepidopteran pests, the most important of which is the cotton bollworm (Helicoverpa zea Bodie) (Lepidoptera: Noctuidae) in the southern United States (U.S.). However, bollworm larvae that survive after consuming Bt toxins may experience sublethal effects, which could alter interactions with other organisms such as natural enemies. Experiments were conducted to evaluate how sublethal effects from Bt toxins incorporated into artificial diet and from Bt cotton flowers impact predation from a lady beetle (Hippodamia convergens Guérin-Méneville) (Coleoptera: Coccinellidae) common in cotton fields of the southern U.S. Sublethal effects were detected through reduced weight and development in bollworm larvae which fed on Bt toxin incorporated diet and Bt cotton flowers. The sublethal effects from toxins incorporated into artificial diet were found to significantly alter predation from third instar lady beetles. Bollworm larvae significantly increased their likelihood of predation after feeding for just three days on diet incorporated with Bt toxins. These results also suggest that the changes in weight and development induced by Bt toxins can be used to help predict predator consumption of bollworm larvae. These findings are important to understanding the level of biological control in Bt cotton where lepidopteran larvae experience sublethal effects.