Molecular Entomology, 2025, Vol.16, No.1, 28-38 http://emtoscipublisher.com/index.php/me 31 Therefore, bee pollination forms a key link in maintaining the structure and function of the ecosystem. When bee populations decline, it often leads to limited plant reproduction and changes in species coexistence, and ecosystem functions may be weakened (Jarpla et al., 2024; Puvača and Brkić, 2024). 3.2 Current threats to global bee populations In recent decades, reports of bee population declines and colony losses have occurred frequently around the world, indicating that bees are facing multiple environmental threats. The harm of pesticides, especially neurotoxic insecticides, to bee health has attracted widespread attention. Field experiments and laboratory studies have confirmed that exposure to pesticides such as neonicotinoids can cause abnormal bee behavior, shortened lifespan, and reduced fertility. The reduction and degradation of pollination habitats are also an important reason for the decline of bees. With the development of agricultural intensification and urbanization, the landscape structure of traditional farmland has been simplified, large-scale monoculture and herbicide use have made wildflower resources scarce, and the nutrition sources and nesting sites of bees have been limited. Surveys show that in areas with fragmented landscapes and poor flower resources, bee colonies are significantly weaker and their overwintering survival rates are also reduced (Branchiccela et al., 2019). In addition, pests and pathogens pose a serious threat to bee populations. The most notorious of these is the Varroa destructor parasite and the viruses it carries. Microsporidia (such as Nosema) and a variety of RNA viruses also threaten bee health, often synergizing with other factors under malnutrition or pesticide pressure. The stress brought by climate change is also beginning to emerge. Climate warming and seasonal disruptions may cause a mismatch between plant flowering and bee activity, resulting in a shortage of nectar sources or the inability to collect high-quality pollen. Soroye et al. (2020) analyzed more than 100 years of data and found that bumblebee species in North America and Europe have experienced a significant contraction in their habitat range, which is closely related to the increased frequency of extreme high temperature events. 3.3 Changes in the ecological environment of bees due to agricultural practices While modern agricultural practices have increased production, they have also profoundly changed the ecological environment on which bees depend for survival. High-intensity pesticide use creates an environment full of chemical risks for bees. Pesticide residues on flowers, polluted water sources and soil may all become ways for bees to be exposed to pesticides. Motta et al. (2022) showed that after bees were exposed to glyphosate, the expression of antimicrobial peptide genes in their bodies decreased and the melanization reaction of body fluids was inhibited, indicating that glyphosate can induce innate immune disorders in bees (Figure 1). The homogenization of farmland structure has changed the nutrition and habitat pattern of bees. Traditional agricultural landscapes include a mixture of cultivated land, woodland and semi-natural habitats, providing bees with a continuous source of food and nests. Intensive agriculture is often a large area of homogeneous land, lacking flowering wild plants and nesting sites. It is difficult for bees to find sufficient and diverse pollen outside the flowering period of crops, resulting in a single nutrition, which in turn affects their reproduction and immunity (Branchiccela et al., 2019). Modern commercial beekeeping methods themselves have also changed the living environment of bees. For example, frequent honey collection and sugar feeding to increase honey production will affect the bee colony's regulation of nutrition; long-distance migration pollination keeps bees in a state of constant stress and prone to disease outbreaks. In addition, around high-density apiaries, large-scale feeding by honey bees may lead to competition with wild pollinators, reducing the latter's food source (Grozinger and Flenniken, 2019; Willcox et al., 2023). 4 Ecological and Genetic Mechanisms of Agricultural Practices Driving Bee Evolution 4.1 Evolutionary impact mechanisms of pesticide use The impact of pesticides on bee populations is not only reflected in individual toxicity, but also in the physiological and genetic adaptation of bees through selection pressure. The evolutionary response of bees to
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