The corn borer's life habits, damage characteristics, and control methods
The corn borer belongs to the order Lepidoptera, family Crambidae (snout moths). It is distributed in Europe, North America, and northwestern Africa; in China the dominant species is the Asian corn borer. The European corn borer is mainly distributed in the Inner Mongolia, Ningxia, and Hebei areas; these provinces are mixed-occurrence zones of the European corn borer and the Asian corn borer, and in Changji it is mainly the European corn borer. The corn borer's host plants include more than 200 species, such as corn, sorghum, foxtail millet, cotton, hemp, legumes, sweet potato, sugar beet, tomato, chili pepper, and wheat.
I. Morphological characteristics
The adult has a wingspan of 25-35 mm and is yellow-brown. The female moth has a stout body, with bright yellow forewings; at the basal 2/3 of the wing there are brown stripes and a brownish wavy line, and on the outer side there is a yellow serrated line. The male moth is slender, with wing color slightly darker than the female; the head, thorax, and forewings are yellow-brown, and the back of the thorax is light yellow-brown. The inner transverse line of the forewing is dark brown and wavy, with the inner side yellow-brown and the base brown; the outer transverse line is dark brown and serrated, with the outer side yellow-brown, and further outward there is a brown band parallel to the outer margin; between the inner and outer transverse lines it is brown, and the hindwing is light brown. In the spore-bearing organ, the spiny region on the abdomen is shorter than the anterior spine-free basal region, usually with 3 spines, sometimes with 2 large spines or 4 spines including 1 small spine; the average number of spines is fewer than that of the Asian corn borer.
II. Life habits
In Changji, the European corn borer has two generations per year and overwinters as mature larvae in corn stalks, root stubble, and ears. Overwintering larvae begin to pupate in early May, the peak emergence period is in mid- and late May, and the peak oviposition period is in mid-June. First-generation adults appear in mid-July, late July to early August is the peak period for adults and eggs, mid-August is the peak period for larvae, and overwintering begins in late September. In Changji it causes severe damage to corn, with the damaged plant rate reaching 20%-80%.
III. Damage characteristics
During the whorl stage of corn, larvae feed on leaf mesophyll or bore into the unexpanded whorl leaves, causing “mosaic leaves.” After tasseling, they bore into the stalks, causing inhibited development of the female ear and reduced yield, and the boring holes are prone to lodging and breakage. During the ear stage, they bore into the female ear and tender kernels, causing kernel loss and mildew and lowering quality. Yield is reduced by 10%-30%.
IV. Control methods
1. After harvest, promptly deal with the stalks of overwintering hosts; this must be completed before the overwintering larvae pupate and emerge.
2. From the beginning of corn borer oviposition to the peak oviposition period, release Trichogramma 2-3 times, at 10,000-20,000 wasps per 667 sq m.
3. Spray 25% diflubenzuron No. 3 suspension concentrate at 600 times dilution or B.T. emulsion, using 200 ml of emulsion containing more than 10 billion spores per gram per 667 sq m; it can also be made into granules and applied.
4. Using Beauveria bassiana powder, apply 100 g of powder containing 5-10 billion spores per gram per sq m of stalks, spraying it on the stack before the corn borer pupates.
5. Mix 0.5 kg of Bacillus thuringiensis powder with 100 kg of fine soil and apply it in spots to the whorl leaves, using 2.5-3.5 kg of inoculated soil per 667 sq m;
6. Use black light traps to attract moths combined with field egg surveys; after determining the number of eggs laid, the hatching progress, and the field damage situation, carry out general control when the mosaic-leaf plant rate reaches 10% at the late whorl stage of spring corn; if it exceeds 20% or there are more than 30 egg masses per 100 plants, another control is needed. For summer corn, control once at the late whorl stage; at the ear stage, when the damaged-ear rate reaches 10% or there are 50 insects per 100 ear silks, control must be carried out immediately. For chemicals, 500 ml of 50% parathion emulsifiable concentrate can be mixed with an appropriate amount of water and 25 kg of sieved coal cinders or sand and gravel, and 1-2 g of granules applied per plant, or 0.16 g of 0.1% cyhalothrin granules per plant. It can also be sprayed with 40% Qixingbao emulsifiable concentrate at 800 times dilution, or 40% synergized fenvalerate, or 5% lambda-cyhalothrin emulsifiable concentrate at 2000 times dilution; in addition, a residual fumigation method can be used. Among the above methods, the most important is to reduce the overwintering base of the corn borer, so as to effectively prevent the occurrence of the corn borer and thereby minimize the occurrence of the pest damage.
Appendix: The corn borer has many natural enemies, mainly egg parasitoids such as Trichogramma and Telenomus, and larval parasitoids such as tachinid flies, Beauveria bassiana, bacteria, and viruses. Predatory natural enemies include lady beetles, ground beetles, and lacewings, all of which have a certain inhibitory effect on the pest population. The corn borer is the main pest of corn. It is mainly distributed in Beijing, Northeast China, Hebei, Henan, Sichuan, Guangxi, and other places. Spring, summer, and autumn sown corn in various regions suffer damage to varying degrees, especially summer sown corn. It can damage all aboveground parts of the corn plant, causing the damaged parts to lose function and reducing grain yield. “The corn borer is not a human being.”