Plutella xylostella larvae harm leaves. Newly hatched larvae can drill into leaf tissue and feed on mesophyll. When it is a little bigger, it will eat the epidermis and mesophyll of the leaves, leaving an epidermis and forming transparent spots, which farmers call skylight opening. The third and fourth instar larvae eat leaves into holes or nicks, and in severe cases, they eat leaves into nets, which greatly reduces the economic value of vegetables. At the seedling stage of vegetables, this kind of insects often gather in the heart leaves to do harm and affect the package of Chinese cabbage, Chinese cabbage and other vegetables. In addition, it also feeds on tender stems, young pods and seeds, which is also a great threat to rapeseed and reserve vegetables. Bioinsecticides for controlling Plutella xylostella mainly include abamectin, matrine, azadirachtin, Plutella xylostella granulosis virus and Bacillus thuringiensis.

(1) Abamectin Abamectin has various contents and dosage forms. Such as 0.5% avermectin EC, the registered dosage is 3-6g of active ingredients per hectare, and the dosage is 40-80ml per mu; 1.8% avermectin EC, the registered dosage is 6.75 ~ 10.8g per hectare of active ingredients, and the dosage is 25 ~ 40ml per mu of preparation. (2) The dosage form of matrine is 0.5% matrine aqueous solution, and the registered dosage is 4.5-6.75g of active ingredients per hectare, and the converted dosage is 60-90ml per mu. Attention should be paid to: ① it is not suitable to mix with alkaline pesticides; ② According to the occurrence of pests, the dosage can be increased appropriately; ③ In the early stage of pest occurrence, the effect is better when the insect age is younger. (3) Azadirachtin uses 0.3% Azadirachtin EC, and the registered dosage is 2.25-4.5g of active ingredient per hectare, and the converted dosage is 50- 100ml per mu. Attention should be paid to: ① it is not suitable to mix with alkaline pesticides; ② Azadirachtin is not quick-acting, but it lasts for a long time, and the effect of seedling protection is more obvious. Therefore, the application interval should not be less than 7 days. Please don't apply 1 time every 3 or 5 days like ordinary pesticides. (4) Plutella xylostella granulosis virus uses 4 billion virus particles/g Plutella xylostella granulosis virus wettable powder, and the dosage is per mu 150 ~ 200 g preparation, and it is sprayed routinely. (5) Bacillus thuringiensis (Bt) preparation uses Bacillus thuringiensis wettable powder 16000 IU/mg, and the dosage is 30-70g per mu, and the preparation is sprayed routinely.