Damage form
Newly hatched larvae drill into the mesophyll tissue of plants to do harm, resulting in small tunnels. 1 at the end of the second instar, it is drilled from the mesophyll to feed on the back of the leaf, leaving only the epidermis on the surface of the leaf to form transparent spots, which farmers call "opening the skylight"; At the age of 3 ~ 4, the leaves are eaten into holes (color plate 23, 13 1), and in severe cases, the leaves are reticulate. At seedling stage, it is often harmful to heart leaves, leaves, stems and pods, which can eat all the seeds and seriously affect the yield of rapeseed.
morphological character
The adult is 6 ~ 7 mm in length, with wings spread 12 ~ 15 mm and grayish brown. The front and rear wings are slender and the cilia are long. The hair on the front wing edge is tilted like a chicken's tail, and there is a yellow-white 3-degree bending longitudinal belt in the center of the wing, forming three yellow-white oblique squares. Eggs are flat and oval, with a size of 0.5 mm ×0.3 mm. They are milky white when they leave the factory, and then turn yellow-green, with a smooth and shiny surface. Larvae is light green. The mature larvae are 10 ~ 12 mm long and have sparse long black hair. The head is light brown, and there are brown dots on the chest back plate, forming a "U" shape. The body segments are obvious, with sharp ends, and the fourth to fifth abdominal segments are enlarged. The whole worm body is spindle-shaped, and the buttocks and feet extend backward. The pupa is yellow-green, spindle-shaped, 5 ~ 8 mm long, with gray silk cocoon outside, and the pupa body can be seen in appearance.
Occurrence characteristics
Five or six generations occur in North China 1 year. In sunny places, pupae overwinter in leaves or weeds. In the spring of the following year, it emerged in April-May. Adults hide under the leaves of plants or other hidden places during the day, and begin to feed, mate and lay eggs after sunset. The peak of activity is from 19 to 2 1. Adults have phototaxis and strong tropism to black light. After eclosion, they can mate, spawn in 1 ~ 2 days after mating, and the spawning period can reach 10 days. Each female lays eggs on average 100 ~ 200. Eggs are scattered or 3 ~ 5 eggs are arranged together, which is more common in the interveinal depression of the back leaves of host plants. The egg period is 3 ~ 7 days. The larval stage is 12 ~ 27 days, which is divided into four stages. Larvae is active, and after being frightened, it wriggles backwards and rotates downwards. Mature larvae spin silk near veins or fallen leaves, and cocoon and pupate. The pupal stage is about 9 days. The developmental threshold temperature of Plutella xylostella is 6 ~ 8℃, and it can survive and reproduce at 10 ~ 40℃. At high temperature, adults have short life span, few eggs and low survival rate of newly hatched larvae. The critical temperature of adults is 42℃, and they can survive for several months at 0 ~ 10℃, but they can still lay eggs below 10℃. The critical temperature of eggs, larvae and pupae is about 35℃. At 0℃, eggs can survive for two weeks and larvae can survive for 42 days. 0℃ has little effect on the first pupa. The resistance of eclosion pupae is weak. The optimum temperature of Plutella xylostella is 20 ~ 30℃. Therefore, spring and autumn are most suitable for Plutella xylostella, which is seriously harmful. The influence of air relative humidity on the growth and development of Plutella xylostella is not very significant, but the mechanical impact of heavy rain or thunderstorm is very unfavorable to eggs and larvae (especially newly hatched larvae), which can cause a large number of deaths. The planting area of cruciferous vegetables and corresponding management measures are one of the ecological conditions that affect the occurrence of diamondback moth. If the overwintering base is large, the cruciferous vegetables are planted in a large area, the varieties are single and the management is extensive, the diamondback moth may occur. The natural enemies of Plutella xylostella include parasitic bees, predatory natural enemies insects, predatory mites, frogs, birds and pathogenic microorganisms. Among them, the quantity control of Plutella xylostella is the most obvious.
Prevention and cure method
(1) agricultural control. Avoid continuous cropping of cruciferous vegetables in a small scale for one year; The early, middle and late maturing varieties and varieties with different growth periods in Cruciferae vegetables are staggered or separated from other vegetables by a certain distance, which interrupts the food chain of Plutella xylostella. Strengthen the management of seedling farm, prevent and control in time, and prevent insects from being brought into Honda. After harvesting vegetables, timely removal of fallen leaves of residual plants in the garden or immediate ploughing can eliminate a large number of insect sources.
(2) Trapping and killing. Plutella xylostella has phototaxis. In adulthood, every 2/3 hectares of vegetable fields are equipped with 1 black light, and the effect will be better if the power grid is added. Trapping and killing with the crude extract of female moth sex hormones: cut off the ventral end of the female moth that emerged that day, and extract it with solvents such as dichloromethane and alcohol, or use 60-mesh nylon wire (or copper wire) as a cylindrical gauze cage with a diameter of 3 cm and a length of 12 cm, and use pots and tripods as rust cages, and put 1 ~ 2 in each cage. Or use 6-8 diamondback moth attractants every 667 square meters, and use a bamboo pole bracket to tie the four corners of a plastic film (33 cm square) to the bracket instead of holding water in a basin. The bait is tied to the bracket with iron wire and bent to the water surface, which is 65,438+0-2 cm away from the water surface and 65,438+00-20 cm away from the vegetables. The bait should be changed every month.
(3) Biological control. Popularize 80 10, 840 1 and Cordyceps No.6. ..
(4) chemical control. Master the chemicals used from the peak of egg incubation to the second instar. 5% carbendazim EC 2000 times, 5% Yitaibao EC 2000 times or 1.8% iveden EC 1500 times, or 500 ~ 600 times of 20% chlorimuron-methyl 1 or 25% chlorimuron-methyl No.3 colloidal suspension, or