Bt Research 2025, Vol.16, No.5, 204-213 http://microbescipublisher.com/index.php/bt 209 5.2 The potential of Bt and nematodes to jointly control soil pests Because soil pests are hidden in feeding areas, conventional spraying is difficult to work, while insect pathogenic nematodes can actively drill into the soil to find hosts, which is a powerful tool for preventing and controlling such pests. The idea of jointly controlling soil pests with Bt and EPN has gradually emerged in recent years. One strategy is to apply poison bait or capsule mixed with Bt at the rhizosphere of the crop, and then water the nematode suspension, so that underground pests are poisoned by ingesting Bt toxins on the one hand, and on the other hand, they are infected and attacked by nematodes (Zhan, 2025). The combined effect of Bt and EPN on Coleoptera grubus was reported: the application of Bt preparations reduced the vitality of Japanese scarabaceous larvae feeding roots in the superficial soil layer and increased the probability of parasitization and death by nematodes. After 7 days of mixing the two, the pest-corrected mortality rate increased by more than 20% compared with nematodes alone (Li et al., 2021). In another field trial of the analworm (Largeraceae pest larvae), synchronous release of Nematodes spores and spraying Bt, the results showed that combined treatment significantly reduced the survival density of the field larvae than any single treatment. The advantage of using Bt in combination with nematodes is that nematodes can penetrate deep into the soil to attack individuals that avoid Bt spraying, while Bt can quickly kill or weaken some surface active pests, reducing the amount of hosts that nematodes need to control. 5.3 Case analysis: research on the control of Bt and nematodes in lepidoptera subterranean larvae Underground pests of Lepidoptera often hide in the soil during the day and go out to feed at night, which brings challenges to prevention and control. A study on Agrotis ipsilon explores the effects of Bt combined with Serrata. In the cornfield experiment, researchers spread wheat bran bait mixed with Bt preparations in the field at dusk for feeding tiger larvae that stung at night; then irrigated and applied the Protozoa nematode suspension at the early morning of the next day to the crop rhizosphere. The results showed that compared with Bt poison bait alone (larval mortality rate is about 60%) or nematode alone (mortality rate is about 50%), the larvae correction mortality rate reached more than 90% after 5 days of combined treatment, and the plant victimized plant rate also dropped below 5%, while the control plots were more than 20% of the victimized plants (Shapiro-Ilan et al., 2002). The experiment shows that the reasonable cooperation of the two biodefense factors can cause continuous blows to ground tigers. From an ecological perspective, the combination also has a complementary coverage: Bt mainly protects the plants from feeding, while nematodes remove hidden insect sources underground, so they control the pests in all stages more thoroughly (Grewal et al., 2005). 6 Bt binds to Plant-Induced Resistance 6.1 Synergies between plant source induced resistance and Bt application Plants themselves have the ability to induce insect resistance, such as after being attacked by insects or dealing with certain provokers, they can initiate a defensive response to reduce further harm. This induced Resistance includes defense pathways mediated by signals such as jasmonic acid (JA), salicylic acid (SA). Using chemically inducing antigens or microbial activators to enhance crop resistance is an important green prevention and control method in the field of plant protection (War et al., 2015). When inducible resistance is applied with Bt, the two may have synergistic effects. On the one hand, plant-induced resistance can reduce the amount of food intake of pests and slow down their development, thereby increasing their sensitivity to Bt. Research has found that plants treated with induced resistance are more difficult to feed by pests, the pests have weak constitutions, and are more likely to be poisoned and die after ingesting Bt toxins. On the other hand, Bt application itself may also trigger the plant's defense response. It has been reported that Bt and its metabolites can induce systemic resistance in crops such as tomatoes and improve plants' resistance to pathogenic fungi and bacteria (Dezhabad et al., 2018). 6.2 Complementarity between Bt and system acquired resistance (SAR) mechanism Systematic acquired resistance (SAR) is a broad-spectrum resistance state formed in the entire plant after locally being infected by pathogens, typically mediated by the salicylic acid pathway. SAR can not only enhance plants'
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