International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.2, 63-73 http://ecoevopublisher.com/index.php/ijmec 67 4.2 Ecological control mechanisms of natural enemy insects Chrysanthemum morifolium exhibits highly specialized ecological defense mechanisms when facing pest infestations. When the larvae of the Spodoptera litura feed on its leaves, they induce the plant to release a series of complex volatile terpenoids (Xu et al., 2021). These herbivore-induced plant volatiles (HIPVs) not only have significant chemical recognition functions, but can also attract predatory or parasitic natural enemies to intervene at a long distance. Through the transmission of this chemical signal, Chrysanthemum morifolium builds a three-trophic-level interaction network covering the plant itself, pests and their natural enemies, showing a coordinated and efficient natural defense strategy. This chemical communication mechanism has multiple regulatory effects on the ecological balance in the field. Volatile terpenes not only directly enhance the search efficiency of natural enemies, but also indirectly affect population dynamics by changing pest behavior. The continuous predation pressure of natural enemy insects significantly reduces pest density and reduces the degree of plant damage (Xu et al., 2021). This natural pest control mechanism based on chemical ecology provides important inspiration for the green prevention and control of Chrysanthemum morifoliumpests. 4.3 Mechanisms of plant-derived pesticides The endophytic microbial community carried by Chrysanthemum morifolium can synthesize a variety of metabolites with disease resistance, showing good pathogen inhibition potential. Studies have shown that the dominant strain distributed in the leaf sphere, Bacillus siamensis D65, can secrete compounds with antibacterial activity, effectively inhibiting the growth and infection of the leaf spot pathogenic fungus Nigrospora oryzae (Sha et al., 2023). This plant-microbe interaction system provides important materials for the development of new green pesticides based on endophytes. At the molecular level, the application of genetic engineering has significantly enhanced the insect resistance of Chrysanthemum morifolium. Studies have shown that after the introduction and high expression of the pyrethroid synthase gene (TcCHS), the plant can stably accumulate pyrethroid alcohol and its glycoside form, thereby producing a dual inhibitory effect on the feeding behavior of aphids through a chemical interference mechanism (Hu et al., 2018). At the same time, the introduction of the TcEbFS gene enables the plant to synthesize (E)-β-farnesene (PEE), which can simulate the warning pheromone of aphids and has a significant repellent function. Further experimental observations found that PEE-8 transgenic plants showed a strong repellent effect on aphids in the S1 development stage, while this defense ability was significantly weakened in the S2 stage (Figure 2), indicating that the accumulation of this type of volatile substances has stage-specific regulatory characteristics (Li et al., 2024). These research results not only reveal the molecular mechanism of chrysanthemum's natural defense, but also provide theoretical support for the construction of an integrated pest management strategy based on temporal regulation. 4.4 Molecular mechanisms of induced plant resistance Chrysanthemum morifolium establishes a multi-level resistance system by finely regulating defense signaling pathways. Salicylic acid (SA) and jasmonic acid (JA) signaling pathways constitute the core defense network, which respond to different types of biological stresses. When attacked by herbivorous insects, the JA signaling pathway is rapidly activated, triggering the synthesis and release of volatile terpenoids (Xu et al., 2021). These volatile organic compounds, as chemical signals, can recruit natural enemy insects from a distance to form an indirect defense. Chrysanthemum morifolium exhibits a complex and highly regulated defense response when responding to pathogen infection. Studies have shown that dodder parasitism can simultaneously induce the activation of two key signaling pathways, salicylic acid (SA) and ethylene (ET) (Liu et al., 2021), reflecting the ability of plants to flexibly adjust their response strategies according to different types of adversities. This synergy and interaction mechanism between signaling pathways constructs a sophisticated and dynamic defense regulatory network,
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