Molecular Entomology, 2025, Vol.16, No.1, 39-49 http://emtoscipublisher.com/index.php/me 45 5.3 Impact of habitat destruction and ecological landscape change With the development of modern agriculture, large areas of land have been reclaimed for farmland, natural vegetation fragments have been reduced, and the landscape has become more monotonous, which has brought many impacts on herbivorous insects and their associated organisms. Habitat destruction and landscape change have produced a "double-edged sword" effect on herbivorous insects: on the one hand, the diversity of some sensitive insects has been reduced, and on the other hand, a few pests that have adapted to the agricultural environment have been given an opportunity to take advantage and even become more destructive (Ziesche et al., 2024). Therefore, it is necessary to seek an optimal balance between landscape and habitat management in agricultural production, and to enhance the homeostasis of farmland ecosystems and the natural inhibitory force on pests through habitat restoration and landscape diversification measures, and to slow down the adverse adaptive evolution and population expansion trends. As some researchers pointed out: "Maintaining the complexity of farmland ecological landscapes is the cornerstone of sustainable pest management and farmland health" (Agrawal et al., 2012). 6 Typical case Study Analysis 6.1 Cotton bollworm (Helicoverpa armigera): multi-host adaptation and resistance evolution The cotton bollworm is an important agricultural pest in the world. One of its notable features is its broad host adaptability and strong ability to evolve resistance (Yang et al., 2022). The cotton bollworm has a very wide host range, and is known to feed on more than 180 plant species, covering a variety of crops such as cotton, corn, soybeans, and tomatoes. This polyphagia stems from its evolutionary pre-adaptation to the chemical defenses of different plants: the cotton bollworm larvae have a variety of detoxification enzymes that can metabolize various plant toxins such as heavy metal phenols in cotton, nicotine in tobacco, and lactones in lettuce. In addition to its broad-spectrum feeding, another outstanding adaptive characteristic of the cotton bollworm is its ability to rapidly evolve resistance to various control measures. The cotton bollworm is one of the first pests found to be resistant to multiple insecticides. So far, it has been reported to be resistant to a variety of insecticides such as organochlorine, organophosphate, carbamate, pyrethroid and Bt protein. Molecular mechanism studies have found that this is mainly due to the kdr (knockdown resistance) mutation of the sodium channel gene in the axon of cotton bollworms, which makes pyrethroids ineffective. At the same time, the activity of carboxylesterase and glutathione transferase in cotton bollworms is also enhanced, which can decompose pyrethroid molecules (Crossley et al., 2021). 6.2 Bemisia tabaci: population replacement, virus transmission and global expansion Bemisia tabaci is a small piercing-sucking pest that occurs widely in greenhouses and fields. It is known for its fast reproduction rate, strong migration and expansion ability, and serious virus transmission damage. Bemisia tabaci is actually a species complex, which contains a variety of cryptic species with obvious genetic differentiation, among which the Middle East-Asia Minor type I (MEAM1, also known as type B) and the Mediterranean type (MED, also known as type Q) are the most well-known (Xue et al., 2024). Different cryptic species differ in host adaptation and pesticide resistance, so population replacement has occurred worldwide. Another major hazard of whiteflies is their ability to spread a wide spectrum of viruses, which indirectly damages crop health (Fiallo-Olivé et al., 2020). Whiteflies suck phloem sap from plants with their mouthparts, and can carry and spread a variety of plant viruses during feeding, especially persistent circulating Gemini viruses. Whiteflies are highly globally expansive pests. They were originally widespread in tropical and subtropical regions, but through international trade and air migration, they have spread to all parts of the world in the past 30 years and are listed as one of the world's top 100 invasive species (Yang et al., 2022). The reason for their spread is that whiteflies are small in size and can easily spread across borders unintentionally with plant materials such as flowers and vegetables; in addition, they reproduce quickly and can quickly establish populations under protected conditions such as greenhouses after arriving in a new environment. 6.3 Spodoptera frugiperda: rapid adaptation in GM crop systems Spodoptera litura (also known as Fall Armyworm) is native to the Americas and is a major emerging invasive pest in the world in recent years. Its rapid adaptation and resistance evolution in GM Bt crop systems have attracted
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