Rice Stem Borers

Five stem borer species are important pest of rice in Asia. They are rice striped borer Chilo supressalis, dark-headed stem borer Chilo polychrysus, rice stem borer Scirpophaga incertulas, rice white stem borer Scirpophaga innotata, and pink stem borer Sesamia inferens. The live cycle, habit and management of the different species and the crop injury they cause are similar and are described together. Identification, distribution, host range and distinguishing characteristics of each species are described separately.

Pest status

Stem borers are widespread in occurrence. They cause significant damage by reducing tiller number even on resistant varieties and are difficult to control with insecticide.

Stem borers occur in all rice environments and are generally most abundant toward the end of the rainy season. Species with wide host ranges are prevalent in upland rice.

Adult. Adults are quiet during the day, hiding among the rice plants or weeds near the field. When disturb they fly only a few meters. The months are active at night and fly to rice fields to lay eggs. Stem borer month are strong flier, but normally range with in 2 km from they origin. Each female lays 200-300 eggs during a lifetime of 4 days. Adult are attracted to a light trap. The greatest number of caught during a new moon.

Egg. Eggs are laid in masses of 5-200 on rice leaves or leaf sheaths. Eggs shape, appearance of the egg mass, and location on the plant are a specific characteristic that vary among species.

Larva. Newly hatched larvae often suspend themselves from leaves by a silken thread and are blown to other plant. Others make a tube form cut leaves, fall on the water, and swim or drift to nearby plants. Young larvae feed on leaves and leaf sheaths.

Medium-aged larvae penetrate the leaf sheath and tiller for several days before entering the stem. Older larvae feed inside the stem may move below the soil surface and hibernate when conditions are unfavorable.

Pupa. Larvae pupate inside the stem near the ground or several centimeters below the soil surface. Adult emerge from the pupa case and crawl out of the rice stem through the exit hole cut previously by the mature larvae.

Striped stem borer

The striped stem borer moth is straw to light brown with silvery scales and a row of black dots at the tip of the fore wing; the hind wing is yellow-white. The eggs are disc-like, pale yellow and overlaps in the egg mass. The larva has a yellow-brown head. It gets its name from three dorsal and two lateral brown stripes along its body. In temperate regions the larvae overwinter in rice straw or rice stubble. The pupa is dark brown.

Plant hosts. The larvae can develop on maize or grassy weeds, but prefer rice.

Distinguishing characteristics.

√ Many larvae may be found in one rice stem.

√ Eggs masses are deposited near the base of leaves or leaf sheaths and are not covered with hair.

√ The striped stem borer is most abundant in temperate regions and in areas that do not flood.

Dark-headed stem borer

The adult moth is straw to light brown with silver scales and several black dots at the tip of the fore wing; the hind wing is yellow-white. The scale like pale yellow eggs overlap in the egg mass. The larva has a black head and black connecting thoracic plate, hence its name. On the abdomen, three dorsal and two lateral brown strip is distinct. The pupa is yellow-brown with two distinct bumps at the front of the head.

Plant hosts. Rice is not the only preferred host (rice, maize, sugarcane, Sacciolepsis, Scirpus, Setaria, Echinochloa).

Distinguishing characteristics.

√ Egg are laid in rows near the base of the leaves and on leaf sheaths, and are not covered with hair.

√ The head of the dark-headed stem borer larva is darker than the head of the striped stem borer larva.

√ One larva generally tunnels in a single stem.

√ The dark-headed stem borer is normally not abundant in rice, except in Malaysia.

Yellow stem borer

The male and female yellow stem borer moths differ in appearance. The male is light brown with numerous small brownish dots, five along the subterminal area and eight or nine near the tip of the fore wing. The female is straw-colored, becoming darker toward the tip, and has a very distinct black spot in the center of each fore wing. The hind wings are pale and straw-colored.

The disc-like eggs are laid in oval batches and are covered with a mat of tan anal hairs from the female moth.

The larvae have a small orange heads. This stem borer gets its name from its pale, hairless yellow body. The larva is over wintering stage in temperate regions. The pupae are elongated and yellow-white.

Plant hosts. The larva feeds only on rice and related wild rices.

Distinguishing characteristics

√ Egg masses are laid near leaf tips and are covered with hair.

√ Only one larva occurs in a stem

√ The pupae are found at the extreme base of the plant, often bellow the soil.

√ The yellow stem borer is most abundant in aquatic habits where flooding occurs and in place where multiple rice crops are grown annually. Larvae seal entrance hole with silk to make stem watertight.

White stem borer

The adult white stem borer is similar to the yellow stem borer in appearance. The male and female appear the same.

The egg masses are identical to those of the yellow stem borer.

The larvae appear like those of the yellow stem borer. The white stem borer pupae tend to be more white-colored than those of the yellow stem borer. These two stem borer can only be clearly differentiated as female adult. They yellow stem borer female has a black spot on each front wing whereas the white stem borer female has no spot.

Plant hosts. Larvae are reported to have a wide host range (millet, rice, wild rice, Pospolum, Panicum, sugarcane, Eleusine).

Distinguishing characteristics.

√ The egg mass, larva, and pupa of the white stem borer are similar to those of the yellow stem borer.

√ The white stem borer occurs predominantly in areas where there is only one wet season rice crop a year and the stubble is left undisturbed during the dry season.

√ The larvae remain dormant at the base of the plants during dry season.

Pink stem borer

Pink stem borer belongs to a family different from that of the other stem borer. It is related to cutworms and armyworms. The adult is robust and tan with dark brown markings. From a central point in the fore wing, a typical radiation of grey-black lines spreads toward in the wings tips, ending in a thin terminal line of dark spot. The hind wings are white.

The bead-like eggs are laid in rows and are not covered with hair. The larva has an orange-red head. Its body is purple-pink on top and white below. The pupa is dark brown and robust.

Plant hosts. The larvae have a wide host range (rice, sugarcane, maize, wheat, barley, oats, wild rice, Panicum, Paspalum)

Distinguishing characteristics.

√ The eggs are laid between the leaf sheath and the stem and are not covered the hair.

√ Larvae may pupate between the leaf sheath and the stem, instead of inside the stem.

Damage

The larvae that have penetrated a tiller feed on the inner surface of the stem walls and thus interrupt the movement of water and nutrients. Tunneling by the larvae weakens the rice stem, which then break easily. Damage depends on the age of the plant when it is attacked.

If damage occurs when the plant are young, the central leaves of the damaged is called deadhearts. If the damage occurs after the spikelets form panicles turn white and no grain filling occurs. The damage panicles are called whiteheads. Tiller damage from diseases such as kresek assembles deadhearts. Drought can also cause whiteheads.

Panicles damage by stem borers can easily be pulled cut buy hand and may show inseck feeding near the base. Stem borer damage tillers are filled with frass (waste from the digestive tract) and have larval entrance and exit holes.

Management

Cultural control

v Plant an early-maturing rice variety. The stem borer completes fewer generations in an early-maturing variety. Populations on such a variety are lower and damage is reduced.

v Plant fields in an area within 3 to 4 weeks, which is less than the time for one stem borer generation. Stem borer complete fewer generations when fields are planted synchronously.

v Field planted later may be severely damage by stem borers that have built up in the fields planted earlier. Stem borers in late planted crops may be carried over to attack a second rice crop. Stem borers on the first crop will not be carried over to the second rice crop if the stubble is plowed under after the first crop is harvest, and the ground is left fallow for at least 3 to 4 weeks between crops.

v Remove rice stubble and straw. Plow stubble immediately after harvest to destroy yellow and white stem borer larvae and pupae.

v Cut stubble close to the ground so that many of the remaining striped, dark-headed, and pink stem borer larvae are removed with the straw. Burn or sun-dry straw after threshing to destroy stem borer larvae.

v Avoid excessive nitrogen fertilizer by splitting fertilizer application.

v Remove seedlings with stem borer egg masses before transplanting

v Flooding a field will not control all stem borers. The yellow stem borer is in fact a major pest of deepwater rice and the larvae can complete their development.

Resistant varieties.

v Many improved varieties have moderate resistance to stem borers. Because some chemicals in the rice plant effect the moth, the plant become less attractive for egg laying and larvae that emerge have a lower rate of survival, are small, and take a longer time to mature.

v High tillering varieties can compensate more for deadhearts during the tillering stage than low tillering varieties can.