Bacterial Microbiota of Field-Collected <i>Helicoverpa zea</i> (Lepidoptera: Noctuidae) from Transgenic Bt and Non-Bt Cotton

• Main Authors: Jean M. Deguenon, Anirudh Dhammi, Loganathan Ponnusamy, Nicholas V. Travanty, Grayson Cave, Roger Lawrie, Dan Mott, Dominic Reisig, Ryan Kurtz, R. Michael Roe
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Microorganisms
• Subjects: <i>Helicoverpa zea</i>; cotton; Bt; resistance; tolerance; microbiota
• Online Access: https://www.mdpi.com/2076-2607/9/4/878

The bollworm, <i>Helicoverpa zea</i> (Boddie) (Lepidoptera: Noctuidae), is an important agricultural pest in U.S. cotton and is managed using transgenic hybrids that produce insecticidal proteins from the bacterium, <i>Bacillus thuringiensis</i> (Bt). The reduced efficacy against <i>H. zea</i> caterpillars of Bt plants expressing Cry toxins is increasing in the field. In a first step towards understanding Bt cotton–bollworm–microbiota interactions, we investigated the internal bacterial microbiota of second–third stadium <i>H. zea</i> collected in the field from non-Bt versus Bt (WideStrike) cotton in close proximity (in North Carolina, USA). The bacterial populations were analyzed using culture-dependent and -independent molecular approaches. We found that WideStrike samples had a higher bacterial density and diversity per larva than insects collected from non-Bt cotton over two field seasons: 8.42 ± 0.23 and 5.36 ± 0.75 (log₁₀ colony forming units per insect) for WideStrike compared to 6.82 ± 0.20 and 4.30 ± 0.56 for non-Bt cotton for seasons 1 and 2, respectively. Fifteen phyla, 103 families, and 229 genera were identified after performing Illumina sequencing of the 16S rRNA. At the family level, Enterobacteriaceae and Enterococcaceae were the most abundant taxa. The Enterococcaceae family was comprised mostly of Enterococcus species (<i>E. casseliflavus</i> and another <i>Enterococcus</i> sp.). Members of the <i>Enterococcus</i> genus can acidify their environment and can potentially reduce the alkaline activation of some Bt toxins. These findings argue for more research to better understand the role of cotton–bollworm–bacteria interactions and the impact on Bt toxin caterpillar susceptibility.