Occurrence, damage patterns and control techniques of the migratory pest diamondback moth
The diamondback moth belongs to the order Lepidoptera, family Plutellidae; aliases: small green worm, two-pointed tip. The diamondback moth is a migratory pest with many occurring generations, strong reproductive capacity, a wide host range, a high level of pesticide resistance, and difficulty of control. It mainly damages cruciferous plants such as cabbage, red cabbage, broccoli, mustard, cauliflower, Chinese cabbage, rapeseed, and radish.
I. Occurrence patterns and damage characteristics
The diamondback moth overwinters as pupae, emerges in March of the following spring, and the adults hide by day and come out at night; when disturbed during the day they make short-distance flights among the plants. The adult egg-laying period can last up to 10 days, with an average of about 200 eggs per female. They are mostly laid in the depressions between veins on the underside of leaves; the eggs are laid scattered or several together, and the egg stage lasts 3-11 days. The larvae have 4 instars in total, with a development period of 12-27 days; the mature larvae spin thin cocoons near the leaf veins and pupate, and the pupal stage is about 9 days. There are two occurrence peaks, from May to June and from late August to November.
The first-instar larvae burrow into the leaf mesophyll to feed, leaving the epidermis, forming transparent patches on the vegetable leaves, "open windows"; the second-instar larvae initially exit from the tunnels to feed on the lower epidermis and mesophyll; the third to fourth-instar larvae can eat the vegetable leaves into holes and notches, and in severe cases the entire leaf is eaten into a net-like pattern. The larvae often concentrate on damaging the heart leaves, affecting head formation. On seed-saving vegetables, they damage the tender stems, young seed pods and seeds, affecting seed set.
II. Control techniques and methods
a. Adopt agricultural measures such as installing insect-proof nets, manual capture and killing, removing old lower leaves of vegetables that carry insects, and protecting natural enemies (such as spiders, frogs and parasitic braconid wasps, Oomyzus sokolowskii) and so on.
b. In areas with good conditions, frequency-vibration insecticidal lamps, black light lamps and sex attractants can be promoted over large areas to trap and kill adults, reducing the number of eggs laid in the field.
c. Biological control, using fungi to control insects: dilute Beauveria bassiana powder with water to prepare a fungal liquid containing more than 100 million live spores per milliliter, or take 30 insect bodies parasitized by Beauveria bassiana per mu, mash them, and mix with 50 kg of water for spraying; Bacillus thuringiensis wettable powder containing 10 billion live spores per gram can also be selected for control.
d. Chemical control: early detection and early control, preferably when there are 50-100 insects per 100 plants and before the second-instar larvae, spraying in the morning or evening. The agents can be selected from: 1) 5% cypermethrin emulsifiable concentrate at 1000 times dilution; 2) 4.5% beta-cypermethrin emulsifiable concentrate at 1000-1500 times dilution; 3) 2.5% bifenthrin at 500-1000 times dilution; 4) 1.8% abamectin at 1000 times dilution, etc.
e. Select insect-resistant (tolerant) varieties, fertilize reasonably, apply heavy organic fertilizer, control nitrogen fertilizer, and increase phosphorus and potassium fertilizer.
f. Avoid planting during the peak occurrence period, planting earlier or later, so that the seedling stage susceptible to insect damage avoids the peak period of diamondback moth damage.
g. Reduce insect sources, arrange crop rotation reasonably, avoid continuous cropping of cruciferous vegetables, and clean the field promptly after vegetable harvest, removing dead branches, fallen leaves and weeds, and carry out intertillage and deep raking to eliminate large numbers of insect sources and lower the pest base.