Bt Research 2025, Vol.16, No.5, 204-213 http://microbescipublisher.com/index.php/bt 207 but also uses Bt to remove larvae that still survive, achieving a higher total host mortality rate. Some studies have compared the effects of Bt and parasitic bees alone and in combination. The results show that when the combination is reasonable, the two have additive or even synergistic effects, and the overall pest mortality rate is higher than any single measure (Hwang et al., 2010). Especially when high-density of pests occurs, parasitic wasps alone may be difficult to parasitize all pests in time, but they can quickly lower the insect mouth with Bt. 3.3 Case analysis: the joint application of Bt and red-eyed wasp in the prevention and control of corn berry Corn borer (Osrinia furnacalis) is one of the main borer pests on corn. Its larvae drill into corn stems for feeding, making it difficult to prevent and control. The strategy combining Bt and red-eyed wasp has been proven to be an effective way to comprehensive prevention and control of corn borer. Trichogramma is a type of obligate egg parasite, which is often used for the biological control of corn borer eggs. Every year during the peak period of corn borer egg laying, the promotion department will guide farmers to release suitable varieties of red-eyed wasps to parasitize and eliminate corn borer egg blocks in the fields. However, some of the eggs may hatch larvae and drill into the corn plant. At this time, combined with spraying of Bt preparations, supplementary strikes can be performed against hatched larvae (Myint et al., 2021). When corn enters the end of the heart leaf stage to the male extraction stage, and when field monitoring finds corn borer eggs hatched sporadically, Bt preparation can be used for foliar spraying, so that the early-aged larvae that feed on corn tissue will intake toxins before invading the stem and become poisoned and died. This two-pronged approach to "egg parasite + larval poisoning" significantly improved the prevention and treatment effect. In the experiments in the corn-producing areas of Northeast China and North China, compared with fields where only chemical pesticides were applied, more than ten per hundred corn were harmed by borers; while in fields that were controlled by "red-eyed wasps + Bt" combination, less than 3 per hundred were injured, and the drilling and borer loss of corn borers was reduced by about 70%~80%, and the prevention efficiency was much higher than a single measure (Wang et al., 2022). 4 Combined Application with Pathogenic Microorganisms 4.1 Complementary effects of Bt and fungal insecticides Like Bt, insect pathogenic fungi are important biological control preparations, but their modes and characteristics are different. Fungal spores can invade through the epidermis of the insect body, and also have an effect on pest stages that do not feed (such as pupae and nymphs), and can remain in the environment for a long time to form effective control. Bt needs to be eaten by pests before it can be poisoned, which has faster effect but shorter residual effect period. The combination of Bt and fungal insecticides is expected to learn from each other's strengths and weaknesses and exert complementary effects. Studies have shown that many fungal-bacterial combinations have significant synergistic effects on target pests (Beris and Korkas, 2021). For example, in the larvae control experiment of Fattia meadow, the 2nd instar larvae were treated with leukoba spore powder and Bt preparations alone, and the mortality rate was only about 21.1% and 65.5% after 5 days; but the larvae mortality rate was as high as 82.6% when the two were mixed. In addition, the combination of the two can also expand the control spectrum. For example, fungi are effective against non-Bt-sensitive pests such as homoptera and acarata, while Bt fills the gap in the lack of rapid-activity of fungi in elderly larvae of Lepidoptera. In practice, Bt and leukobassium can be mixed into a composite preparation, or applied sequentially on the same insect state, thereby improving overall prevention (Beris and Korkas, 2021). 4.2 Bt and bacterial pesticide potential In addition to Bt, some other bacteria also have insecticidal activity, such as Lysinibacillus sphaericus, Bacillus thuringiensis, and some Gram-negative bacteria. Among them, Bacillus spherical is mainly used to prevent and control mosquito larvae, and is particularly effective against Culex, Anopheles, etc., but is ineffective against mosquito pests; on the contrary, Bt has limited effect on mosquitoes. Combining Bt with other bacterial source pesticides can expand the prevention and control spectrum and exert synergistic effects. A classic example is in the field of anti-mosquito larvae: the mixed administration of Bt israelensis (BtI) and Bacillus spherical (Bs) was
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