Abstract
BACKGROUND: Resistance of Busseola fusca (Lepidoptera: Noctuidae) to Cry1Ab was documented in 2006, 7 years after the first cultivation of MON 810 in South Africa. This was mitigated by introducing a second-generation Bacillus thuringiensis (Bt) maize (MON 89034), which contains the Cry1A.105 and Cry2Ab2 proteins. The first reports of B. fusca infestations of MON 89034 maize came in the KwaZulu-Natal province (2017-2018 cropping season), followed by reports in the Mpumalanga province (2022-2023 season). Here we report results of artificial diet- and plant-based laboratory assays to assess the susceptibility of B. fusca populations to the Bt proteins in MON 89034. RESULTS: Larvae were sampled from nine locations which included three where greater than expected injury due to B. fusca had been reported to MON 89034. Larval mortality in assays with diet-incorporated Cry2Ab2 protein was 100% for all except the three problem populations, showing that the Cry2Ab2 protein in MON 89034 is highly efficacious against B. fusca. In contrast, assays with Cry1A.105 did not cause significant mortality in any of the B. fusca populations including larvae from a susceptible reference. Larval survival on leaf tissue of MON 89034 maize after 7 days ranged between 75% and 91% for the three problematic B. fusca populations, compared to 0.4% to 9.6% for the five other populations. CONCLUSION: Therefore, MON 89034 is effectively a single-mode-of-action technology against B. fusca and carries an inherent high risk for the evolution of resistance. This study shows that the three B. fusca populations collected from locations with greater than expected damage to MON 89034 have resistance to the Cry2Ab2 protein and therefore to MON 89034 maize. This research emphasizes the importance of resistance monitoring and implementation of effective insect resistance management tactics. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.