The Life Habits, Damage Characteristics, and Control Methods of the Lepidopteran Pest Corn Borer
The corn borer belongs to the order Lepidoptera, family Crambidae. 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, while Changji is mainly the European corn borer. The host plants of the corn borer include more than 200 species of plants such as corn, sorghum, foxtail millet, cotton, hemp, legumes, sweet potato, sugar beet, tomato, 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 and bright yellow forewings, with brown stripes and a brown wavy line at the basal 2/3 of the wing, and a yellow serrated line on the outer side. The male moth is slender, with wing color slightly darker than that of the female; the head, thorax, and forewings are yellow-brown, and the dorsal side 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; the area between the inner and outer transverse lines is brown. The hindwings are light brown. In the spore organ, the abdominal spiny region is shorter than the anterior basal spineless 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 mid- to late May, and the peak egg-laying period is 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 larval period, 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 the leaf mesophyll or bore into the unexpanded whorl leaves, causing “shot-hole” symptoms. After tasseling, they bore into the stalks, impeding female ear development and reducing yield; the bore holes are prone to lodging and breakage. During the ear stage, they bore into and feed on female ears and tender kernels, causing kernel loss and mold, and lowering quality. Yield is reduced by 10%-30%.
IV. Control Methods
1. After harvest, promptly handle the straw of overwintering host plants; this must be completed before the overwintering larvae pupate and emerge.
2. From the beginning to the peak of corn borer egg laying, release Trichogramma 2-3 times, at 10,000-20,000 individuals per 667 sq m.
3. Spray 25% diflubenzuron No. 3 suspension concentrate at 600 times dilution or B.T. emulsifiable concentrate, using 200 mL per 667 sq m of an emulsifiable concentrate containing more than 10 billion spores per gram; it can also be made into granules for broadcast application.
4. Using Beauveria bassiana powder, apply 100 g per sq m of straw of a powder containing 5-10 billion spores per gram, 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 spot-wise into the whorl, using 2.5-3.5 kg of bacterial soil per 667 sq m.
6. Use black-light lamps to trap moths combined with field egg scouting. Based on the number of eggs laid, hatching progress, and field damage, when the shot-hole plant rate reaches 10% at the late whorl stage of spring corn, carry out general control; if it exceeds 20% or there are more than 30 egg masses per 100 plants, another control application is needed. For summer corn, apply control once at the late whorl stage; at the ear stage, when the damaged ear rate reaches 10% or there are 50 larvae per 100 ears on the silks, control must be carried out immediately. For pesticides, 500 mL of 50% parathion emulsifiable concentrate can be mixed with an appropriate amount of water and 25 kg of sieved cinder or sand-stone and stirred evenly, then 1-2 g of granules applied per plant, or 0.16 g per plant of 0.1% fenvalerate granules. It can also be sprayed with 40% Qixingbao emulsifiable concentrate at 800 times dilution, or 40% synergized fenvalerate, or 5% fenpropathrin emulsifiable concentrate at 2000 times dilution; in addition, a residual fumigation method can also be used. Among the above methods, the most important is to reduce the overwintering population 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 including 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 a major 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 suffers damage to varying degrees, especially summer-sown corn, which is the most severely affected. 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 human."