Bt Research 2025, Vol.16, No.4, 168-181 http://microbescipublisher.com/index.php/bt 174 inhibitory effect on the number of regional pest groups, indirectly protecting the surrounding fields where Bt crops are not planted, and reducing the pest base of the entire agricultural ecosystem (Yang et al., 2022). This is called the "regional area effect" and has been reported in cotton producing areas in China and the United States. The reduction in pesticide use not only saves prevention and control costs, but also brings environmental and health benefits. For example, the number of natural enemy insects (such as ladybugs, snails, spiders) in Bt cotton fields is significantly higher than that in conventional cotton fields because pesticide reduction reduces damage to natural enemies. To a certain extent, the recovery of natural enemies can also suppress the outbreak of non-target pests such as cotton aphids, achieving the synergistic effect of biological control and genetically modified control. 5.2 Effect on crop yield and quality Bt genetically modified crops usually show improvements in yield and quality by reducing pest loss. First, in terms of yield, numerous studies have confirmed that Bt crops have a significant advantage in increasing yield in medium and high pest years than non-Bt controls. In terms of cotton, serious harm to cotton bollworms in traditional cotton fields can lead to a 30% reduction in yield or even a failure to obtain. However, due to the low insect density of Bt cotton, the peach sitting rate and single bell weight have significantly improved. According to experiments in many provinces in China, the increase in yield of Bt cotton compared with conventional cotton is generally 10%~20%, and the increase in yield can reach more than 30% in years of high incidence of pests. In terms of corn, due to the decay of corn borers and other food, the fruiting rate decreased and the bald tip increased, traditional corn yields decreased by 20% in heavy insect pest areas; while Bt corn kept the ears and grains intact, and the routine yield increased by 5%~10%. According to the US Department of Agriculture, the average Bt corn increased by about 7.1 bushels per hectare (≈0.45 tons), mainly from the reduction of pests. Bt strain tests of soybean and rice also showed significant increase in yield compared with untransgenic controls without drug administration. For example, the yield in the fields of Bt rice strains in South China in China increased by about 8% compared with the control, and quality indicators such as the whole-sum rice rate has also increased (Yang et al., 2022). It can be seen that Bt crops have achieved the role of stabilizing and improving yield by ensuring healthy growth of crops. As for quality, the inherent quality of Bt crops is basically equivalent to or improved by conventional varieties. The quality of cotton fibers (length, specific strength, etc.) is mainly determined by the genetics of the variety, and the transfer to the Bt gene has no obvious side effects on the fiber traits. 5.3 Environmental adaptability and climatic factor effects of Bt crops Field performance of Bt crops is also affected by environmental and climatic factors. In most cases, normal environmental variations (such as temperature and precipitation changes) do not weaken the anti-worm effect of Bt crops, but extreme conditions may affect the expression and stability of Bt proteins. For example, some studies have observed that under high temperature and drought conditions, the content of Cry1Ac toxic protein in Bt cotton leaves decreased by 20%~30%, resulting in a decrease in the toxic activity of cotton bollworms (Jin et al., 2023). High temperatures may reduce its accumulation by affecting the structure of Bt protein or cotton plant metabolism. In addition, continuous high temperatures and low humidity may also accelerate the degradation of Bt protein in plant tissues. Salt-alkali stress is another factor. Laboratory experiments have shown that when soil salt concentration is high, the Cry1Ac content in Bt cotton leaves and buds decreases significantly (about 40%~70%), and the pest resistance decreases accordingly. The impact of waterlogging on Bt crops is also worth noting. Researchers found that long-term water flooding of cotton will reduce the total amount of Bt protein. It is necessary to wait until the flooding recovers before the cotton plant can restore normal insect resistance levels (Ahmad et al., 2020). In addition, optimized fertilization can also enhance the expression of Bt protein. It has been reported that sufficient supply of nitrogen fertilizer can increase the Cry1Ac content of Bt cotton leaves by about 14%, enhancing resistance to cotton bollworms. 5.4 Case analysis: field performance of Chinese Bt cotton in the yellow river basin The cotton area in the Yellow River Basin (including Shandong, Henan, northern Hebei and other places) is an
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