Recently, a study from the Chinese Academy of Agricultural Sciences discovered the molecular mechanism of high resistance of diamondback moth to Bt insecticidal protein evolution. This study reports for the first time internationally a midgut transcriptional regulatory loop as a key "regulatory shield", providing a new perspective for elucidating the molecular mechanism of insect Bt resistance. The research results were published in the renowned journal "The Innovation" under the umbrella of Cell. In agricultural production, pest damage is a major challenge, therefore, people usually use insecticides to control these pests. However, there is a problem with the long-term extensive use of insecticides: pests will continue to evolve insecticide resistance. This seems to be an endless race, as humans constantly develop new insecticides and pests evolve new insecticide resistance. There is a globally significant agricultural pest called the diamondback moth, which causes global economic losses of up to 4-5 billion US dollars annually. More importantly, the pest has developed severe resistance to almost all insecticides. So, how does the diamondback moth develop resistance to insecticides? Researchers have found that an increase in the level of molting hormone (20E) in the body of diamondback moths is a key factor. When diamondback moths develop resistance to Bt insecticides, their levels of 20E in their bodies significantly increase, thereby resisting the toxic effects of Bt insecticides. But why does the 20E content in the body of diamondback moth increase? This is the new discovery of the study: the transcriptional regulatory loop in the midgut of the diamondback moth (PxDefd/miR-8545/PxGLD/20E/PxDefd) plays an important role in it. Transcription factors and miRNAs in the transcriptional regulation loop, as important regulatory factors for transcriptional and post transcriptional regulation, can regulate the change of gene expression. In this study, the research team found that PxDsd is a key transcription factor, and a decrease in its expression level leads to an increase in the expression of miR-8545 in the midgut, which in turn inhibits the expression of a glucose dehydrogenase (GLD) gene. Glucose dehydrogenase is a newly discovered 20E degrading enzyme, and when its expression is inhibited, the content of 20E significantly increases. Generally speaking, after pests evolve drug resistance, it will result in certain fitness costs, such as increased mortality rates, growth and development stagnation, and reduced offspring numbers. These costs are like fines imposed on pests for developing drug resistance. However, surprisingly, after evolving high resistance to Bt insecticides, the diamondback moth was not penalized and still lived freely. So, how did the diamondback moth achieve this? Researchers have found that when the 20E content in the body of resistant diamondback moths excessively increases, the expression level of PxDefd is inhibited through a negative feedback regulatory pathway to reduce the 20E content, thereby forming a transcriptional regulatory loop (PxDefd/miR-8545/PxGLD/20E/PxDefd) in the midgut of diamondback moths to regulate the moderate increase of 20E content, thereby maintaining the homeostasis of 20E in diamondback moths and successfully avoiding being penalized while forming resistance to Bt insecticides. This discovery not only reveals the molecular mechanism of resistance of diamondback moth to Bt insecticides, but also provides new ideas for agricultural production. In the future, we can inhibit the growth and development of pests and the evolution of drug resistance by changing any link in the midgut transcriptional regulation loop, thereby more effectively controlling pests and protecting crops from pest damage. (New Society)