Agricultural insect pests damage crops, causing a significant economic loss to the farmers as well as impacting and threatening the global food security. One smart solution is genetically modified crops (GM Crops) to produce proteins from the bacterium Bacillus thuringiensis (Bt), which are toxic to certain insects and safe on non-target organisms. Growing Bt crops has seen rapid rise in the US with over 80% of the areas planted with corn and cotton in the last eight years. Although Bt-modified crops have successfully controlled insect damage in some crops, some insects evolved to become resistant to Bt toxins.
The first Bt crops – Bt corn with Cry1Ab and Bt cotton with Cry1Ac were introduced commercially in 1996, effective against certain lepidopteran species. Then, more insects targeted by Bt crops produced cry toxins in the United States. Since the early release of Bt crops, scientists have extensively monitored the inevitable evolution of insect resistance. Transgenic hybrids expressing two or more Bt proteins, called pyramids, with unique modes of action have been deployed to mitigate resistance evolution. Data monitoring of field-evolving resistance to ten Bt toxins in 22 lepidopteran species and two beetle species were reported recently. Cases of practical resistance, where over 50% of the population carried resistant alleles, decreased the efficacy of Bt crops. Most of the practical resistance cases were in three destructive species:
Fall armyworm Spodoptera frugiperda: In the USA, S. frugiperda is controlled by Bt corn and cotton-producing combination of Cry and Vip3A insecticidal proteins. Cases of practical Bt-resistant S. frugiperda have been reported from Puerto Rico to two Cry toxins, Cry1F and Cry1Ac, and from Florida and North Carolina to three Cry toxins, Cry1F, Cry1Ab, and Cry1A.105.
Corn earworm Helicoverpa zea: Field data from Arkansas, Louisiana, Mississippi, Tennessee, and Texas show efficacy decrease for Bt cotton producing the hybrid Cry1Ac + Cry1Fa or Cry1Ac + Cry2Ab. However, the efficacy increased significantly when the pyramided hybrids of Cry1Ac + Cry1Fa +Vip3Aa were introduced in Bt cotton.
Western corn rootworm Diabrotica virgifera virgifera: Destructive damage of WCR has been managed by Cry3-Bt corn; these included Cry3Bb1, Cry34/35Ab1, and mCry3A and were released as single-protein hybrids. But reports on the field-evolved resistance to Bt corn with Cry3Bb1 toxin rushed the need to commercialize Bt pyramids, including Cry3Bb1 + Cry34/35Ab1, mCry3A + Cry34/35Ab1, and mCry3A + eCry3.1Ab. Recent research found WCR resistance to Cry34/35Ab1 in Iowa and Minnesota, and the hybrid Cry3Bb1 + Cry34/35Ab1 was found in Nebraska fields.
Academic and AgTech scientists are exploring new strategies to heighten the efficacy of Bt crops tirelessly. Integration RNA interference (RNAi) targets along with Cry toxins in Bt crops, or enhancing the durability of the existing Cry toxins can be two fundamental approaches to slow down insects’ resistance to Bt toxins and Bt crops.
As the world continues to evolve, Agro BioResearch LLC commits to delivering excellence with advancing technology. As part of our contribution to sustainable agricultural management and pest management solutions, we aim to empower innovation in Bt Crop technology and introduce the findings to the market. With a team of experts at the forefront of agricultural research, Agro BioResearch LLC specializes in designing comprehensive evaluation studies to test the efficacy of novel products against Bt-resistant insects. We have licensed APHIS-USDA permits to test the following strains:
Fall armyworm, a Bt-resistant strain to Cry1A and Cry1F toxins.
Western corn rootworm, a Bt-resistant strain to Cry3 toxins.