Recently, farmers in the Central South China Cotton Region have generally reported that insect-resistant cotton exhibits poor insect resistance and is not resistant to insects. Is insect-resistant cotton really resistant to insects? the answer is negative. We should understand the insect-resistant characteristics and characteristics of insect-resistant cotton so that effective measures can be taken to prevent it.
1. Insect-resistance characteristics The transgenic Bt gene controlled by Bt gene has a relatively single insecticidal effect, and it only has a significant poisoning effect on Lepidoptera pests. It can seriously block the death or growth of poisoned bollworms, thus controlling the occurrence of cotton bollworms. Harm. Under normal conditions, their insect-resistant genes can be well expressed and have a strong ability to resist insects. However, insect-resistant cotton is not a non-insect-free cotton, and it is still necessary to control it according to local conditions, otherwise it will also cause harm.
Second, the national standard for insect-resistant cotton The following provisions are made on whether the insect-resistant cotton and resistance grading are as follows: First, the toxic protein content standard, the cotton field is randomly selected from the second and third true leaves of cotton plants for testing its toxic protein content, 200 The above is insect-resistant cotton, with 400 or more as high resistance; secondly, the second-generation cotton bollworm beetle damage reduction rate standard, without the use of chemical control, the insect-resistant cotton than the conventional cotton bud bell damage reduction rate of 50% to 60 % for the anti-grade, 60% ~ 80% for the high resistance level; third is the third generation of the indoor insecticide test mortality rate of Helicoverpa armigera, collecting the second true leaf of the top of the cotton plant for insecticide test, larval corrected mortality rate of 40% ~ 60 % is medium resistance, 60% to 80% mortality rate is anti-grade, mortality rate is more than 80% is high resistance; 4 is the standard of field resistance rate, taking random sampling in the field, and the rate of insect-resistance strain exceeding 90% is confirmed as Insect-resistant cotton, more than 95% reached a high level of resistance standards. It can be seen that insect resistance is relative.
III. Causes of poor insect resistance of insect-resistant cotton In general, the insect-resistant genes of insect-resistant cotton can be fully expressed and have a strong resistance to cotton bollworm. However, due to external environmental conditions, insect-resistant genes are sometimes encountered. Can not be fully expressed, so that the ability of insect resistance weakened or lost, mainly caused by: First, the variety of varieties, due to the breeding of insect-resistant cotton to take more hybrid methods, such as breeding, so the general offspring have a separation phenomenon, plus Cotton has a 3% to 5% natural bunching phenomenon, coupled with the influence of high temperature, drought and other factors, the field is prone to non-insect resistant plants. The second is the degradation of varieties. After selection and cultivation of insect-resistant cotton varieties, if they are not selected and purified and rejuvenated after successive years, degradation will occur and the insect-resistant ability will decline. The third is the impact of climate and cultivation conditions. In normal climate and cultivation conditions, insect-resistant genes can be well expressed, but in the case of high temperature, drought, or due to nutrient imbalances, resistance gene expression is poor or silence , thereby reducing or losing resistance to insects.
IV. Insect resistance of different organs of cotton plants The order of resistance to insects of various organs of cotton plants identified by scientific research units is: the tender tip is larger than the young leaves, the young leaves are larger than the old leaves, the leaves are larger than the buds, and the buds are larger than the flowers. Cotton buds and flowers are poor in insect resistance, so if bollworm eggs are produced on buds and flowers, cotton bollworms are likely to survive, causing damage to some cotton plants.
V. Influence of “Natural Law†Due to the long-term planting and promotion of insect-resistant cotton, affected by the natural selection rule, it is easy to produce resistant H. armigera, and the insect-resistant cotton will reduce or lose insect resistance efficiency against H. armigera.
In summary, insect-resistant cotton is not insectless cotton, and it is still necessary to carry out field inspections during the occurrence of cotton bollworms. Once prevention and control indicators are reached, prevention and control must be stepped up. Otherwise, it will cause varying degrees of harm if missed the critical period of prevention and control. For example, isolated mutants that are not resistant to insects in cotton fields can be removed to prevent cotton bollworms growing on this cotton plant from transferring to neighboring cotton plants. The key period of prevention and control of the bollworm is three days after the peak of egg laying, and the larva hatching period; the second generation of cotton bollworm prevention and control index, more than 20 eggs per 100 eggs, more than 100 third-instar larvae must be immediately carried out. Prevention and control, general control 1 to 2 times, prevention and control three times a year; three generations of Helicoverpa armigera more than 50 eggs, more than 10 third-instar larvae will immediately prevent and control, general control 2 to 3 times.
The use of single drugs should be avoided during the prevention and treatment in order to avoid poor control and attention should be paid to alternating use of drugs. When using a new type of pesticide, its active ingredients and contents should be clarified, and instructions should be followed. Spray time should be controlled before 10 am and after 5 pm. And spraying should not be too fast when spraying, spraying should be uniform to ensure the quality of prevention.
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