Major Insect Pest of Maize
a) Maize stem borer, Chilo partellus; Lepidoptera: Pyralidae
It is serious pest of maize. Adults are relatively small moth with brown in colour measuring 7- 17mm in body length with wing expansion of 26mm. Females has much paler forewing while male has pale brown forewing. They also attack on other hosts such as sorghum, finger millet and sugarcane. This pest is more severe in areas of maize-rice cropping system and less in hills as compared to terai region.
Eggs 4-5 days Larva 16-41 days Pupa 5-8 days Adult
Maize stem borer exhibits complete metamorphosis, including egg, larval, pupal and adult stages. The adult are active at night, when they mate and lay eggs on the underside of leaves of various host plants particularly maize and sorghum. Eggs are flat, oval, yellowish and are laid in overlapping clusters each containing upto 20 eggs. Within about a week eggs hatch into larvae which enter into the stem and proceed downwards. Young tender plant die due to the death of main stem whereas in mature plant they also attack on tassel and cobs. Plants are week sometimes may fall in wind. Life cycle completes inside the cobs and stems. The larval matures in 16 – 41 days passing through 6 stages. The pupal period is completed inside the whorl. The total life cycle of MSB is probably 5 generation in a year. After harvesting maize in June-July, Adult harbors into the ratoon of rice where pupae overwinter until March-April and they again re-enter in maize crop.
Damage: Caterpillars are destructive causing direct damage to plant. A newly hatched larva first feed on leaf sheath which show transparent patches and later on turn yellow-brown and eventually dries up. Larvae feed on the soft tissues and make tunnel through the stem. Stems become weak and easily break down. Feeding of central part of plant causes “dead heart” in vegetative stage while causes “white ears” in reproductive stage.
Management: destruction of infested plants as they serve as the carriers fed such to livestock. Use granules like Carbofuran inside the stem before they enter. Do not feed such plants to animals. Other liquid chemicals like Methyl parathion and Endosulfan can be sprayed on the affected parts.
b) White grubs (Phyllophaga rugosa, Anomala sp.); Coleoptera: Scarabaeidae
They are the young one of beetles having red brown head with white body. Larvae are primarily harmful whereas the adult also tear the leaves and attachment portion of maize and other vegetables. Larvae are three instar and second and third instar are harmful. Adult lays eggs on grass or on the fresh dung. Upon hatching into the grubs within about 3 weeks they start to feed on the root of maize and grass. Inside soil they can live quite a long period up to 20 months. Pupal period lasts for about 6 months and reappears again as the beetles during May-June.
Management: removable of weed hosts by cleaning nearby area. Do not use fresh dung. Deep ploughing after harvesting the crop allows exposure of grubs above ground which could be prayed by the bird and other natural enemies. Light trap may help monitoring and if we increase the number of traps which may help in trapping out adult population.
Larvae are effectively controlled using insects pathogenic fungi (Metarhizium anisopliae). It is green muscardine fungus also produced for the first time in IAAS, Rampur, chitwan Nepal within the PhD study. It can also be managed using white muscardine fungus (Beauveria bassiana). These bioagents may not bring down quick control as pesticides does but may lower the pest population after some time and very useful for environment, human beings and non target organisms.
c) Army worm; Mythimna separate; Lepidoptera: Noctuidae
Host: Rice, wheat, Maize
It is one of the important pests of rice and maize. Adult is brown moth with distinct white spot on middle of forewing. Larvae are green to brownish pink in color.
Eggs 7-9 days Larva 20-25 days Pupa 9-29days Adult (On leaf sheath) (4-5 stage)
During the early instars, the larvae feed on the mesophyll of the leaf tissue. The 3rd and later larval instars feed gregariously on the foliage the larvae reach the earhead in the final or sixth moulting and cut the rachis. Mature larvae, which are voracious feeders eat the older leaves and skeletionize them.
Damage: Larvae are most destructive in nature and feed on young leaves. When their number is high they even feed on the stem and leaves leaving behind main vein only. They cut the ear of rice plant and hence named “Rice ear cutting caterpillar”. In heavily infested condition, field looks like just grazed by cattle or damaged by mice.
- Deep ploughing of field after harvesting of rice.
- Flooding of field after crop harvest.
- Avoid excessive use of nitrogenous fertilizer.
- Installation of light trap in the field.
- Spray Fenitrothion 50% EC @1ml/liter water.
d) Field cricket, Brachytrupes portentosus; Orthoptera: Gryllidae
Live inside the soil by making deep hole. Both the nymph and adult fed on (cut) the young plants at the soil surface which they carry inside the hole. They also attack other cereals. Host: maize, wheat, oat, millet
Damage: Both adult and nymph cut the young seedling. They cut spike and ear of the plant, which they carry inside the hole. Live inside soil by making deep hole in rotten wood)
- Deep ploughing of field in winter season.
- Flooding of the field.
- Plant bamboo near the maize field so that owl lives in bamboo and attack upon cricket. 4. Blue type of wasp is predator of this insect.
- Spray Fenitrothion 50%EC@1ml/ltr water.
e) Seed bed beetle (Heteronychus lioderes); Coleoptera: Scarabaeidae
They are soil pests. Larvae fed on the base of young seedling at soil surface and underground roots. Life cycle and management is similar as described in grubs.
f) Flower beetle; Chiloloba acuta; Coleoptera: Cetonidae
If they occurred in large number, cause destruction the anther and stigma of Rice, Maize, and Sorghum etc. They also feed on the leaves, buds and flowers. They cause damaging blossom petals by making small holes.
Egg 4-10 days larvae pupa Adult (Lays on leaf or (3-5 stages)
Lecture note on Economic Entomology by N.B. Singh
- Collection of adults with the help of sweep net.
- Use of suitable chemicals.
g) Wire worms, Agriotes spp.; Coleopteran: Elateridae
Host: Cereals, potato, carrot and other root crops.
Wireworm is the common name for the larvae of click beetles and larval stages are more destructive than the adult stages. Wireworm is slender, hard-bodied “worm” particularly found in moist soils. The adult known as click beetle, because of its habit of clicking or snapping its body into the air, when pushed on its back.
Damage: They damage germinating seeds and base of stem close to soil. It is severe in maize and potato.
Egg 2-4 week Larvae 2-6 week pupa 1 week Adult (Around root Zone) (mostly cause damage) (in soil)
- Follow crop rotation with Alfalfa.
- Planting wheat around Maize field as trap crop.
- Field drying and summer ploughing to reduce larval population.
- Use Beauveria and Metarrhizium.
- Flooding of field at least once in a week.
high seed rate and seed treatment need to be followed against soil pests. As a result, pest like seed bed beetles are reluctant to feed on (cut) newly growing seedlings. Some of the soil acting chemicals BHC, Aldrin and Chlordane can also be used during land preparation. Many insects can be minimized by making healthy crop growing with balance use of inputs and adjustment in sowing dates.