Occurrence regularity, damage characteristics and control techniques of migratory pest Plutella xylostella

Plutella xylostella is a lepidoptera family, alias: small green insects, two tips. Plutella xylostella is a migratory pest with many generations, strong reproductive ability, wide host range, high resistance level and difficult to control. It mainly damages cruciferous plants such as cabbage, purple cabbage, broccoli, mustard, cauliflower, cabbage, rape and radish.

1. Occurrence law and damage characteristics

Plutella xylostella overwinters as pupae and emerges in March of the next spring. Adults lie in the daytime and emerge at night. When frightened in the daytime, they fly a short distance between plants. The adult oviposition period can reach 10 days, and each female lays about 200 eggs on average. The eggs are scattered or several grains together. The egg stage is 3-11 days. The larvae have 4 instars and the development period is 12-27 days. The mature larvae form cocoons and pupate near the veins. The pupal period is about 9 days. There are two peaks in May-June and late August-November.

The first instar larvae dive into the mesophyll to feed, leaving the epidermis, forming transparent patches on the leaves,"opening the skylight," withdrawing from the following channel at the beginning of the second instar to feed on the lower epidermis and mesophyll, the third to fourth instar larvae can eat the leaves into holes and notches, and the whole leaves are eaten into a network when serious. Larvae often concentrate on damaging the heart leaves and affecting the heart. On the reserved seed vegetables, it damages the tender stems, young seed pods and seeds, affecting the fruiting.

II. Control techniques and methods

a. Agricultural measures such as covering insect nets, killing artificially, removing old leaves with insects at the lower part of vegetables, protecting natural enemies (such as spiders, frogs, parasitic cocoon bees and cabbage moth biting bees), etc.

b. Frequency-vibrating insecticidal lamps, black lamps and sex attractants can be widely promoted in areas with good conditions to trap adults and reduce the number of eggs dropped in the field.

c. Biological control, using bacteria to control insects, diluting Beauveria bassiana powder with water to prepare bacterial solution containing more than 100 million live spores per ml or smashing 30 insects parasitized by Beauveria bassiana per mu, adding water to spray 50 kg; Bacillus thuringiensis wettable powder containing 10 billion live spores per gram can be selected for control.

d. Chemical control, early detection and early control, preferably 50-100 insects per 100 plants, before the second instar, spraying in the morning or evening. The pesticide can select ①5% cypermethrin emulsifiable concentrate 1000 times solution;②4.5% beta-cypermethrin emulsifiable concentrate 1000-1500 times solution;③2.5% bifenthrin 500-1000 times solution;④1.8% abamectin 1000 times solution, etc.

e. Selection of insect resistant (tolerant) varieties, rational fertilization, heavy application of organic fertilizer, control of nitrogen fertilizer, increased application of phosphorus and potassium fertilizer.

f. Avoid the peak period of planting, early or late planting, so that vulnerable seedlings avoid the peak period of diamondback moth damage.

g. Reduce insect source, reasonably arrange crop rotation, avoid continuous cropping of cruciferous vegetables, clean garden in time after vegetable harvest, remove litter and weeds, and cultivate and rake deeply to eliminate a large number of insect sources and reduce pest base number.