RICE BROWN PLANTHOPPER

Nilapavarta lugens is probably the most serious insect pest of rice in Asia. Its feeding causes plant wilt and cause a symptom called hopperburn. it also transmits grassy stunt and ragged stunt virus diseases.

Pest status

The rice brown planthopper has a high capacity to reproduce. Frequently, farmer misuse of insecticide causes outbreaks of hopperburn and/or virus diseases over large areas. The development of biotypes often reduces the life-span of resistant rice varieties. The effectiveness of control by insecticide is lessened because the hoppers are found at the base of plants and the crop canopy acts as an umbrella to protect the insect from spray droplets.

The brown planthopper is mainly a pest of irrigated wetland rice, but it can also become abundant in rainfed wetland environment. It is rare in upland rice.

Development

Five nympha stage

Egg Small nymph Large nymph Adult

Adult. Short winged (brachypterous) and long-winged (macropterous) adult occur is both sexes. Short-winged forms cannot fly but remain in the field to feed and reproduce. Long winged form disperse.

Macropterous females lay about 100 eggs and brachypterous female 300 eggs during a lifetime of about 2 weeks. Openings for eggs are made in the tillers by the saw-like ovipositor.

Adult such the plant sap from the base of plant where they stay day and night. Long-winged adult are highly attracted to a light trap. Highest catches occur during full moon.

A related species, Nilapavarta bakeri (Muir), often confused with the brown planthopper, is found in light trap collection but is not a pest of rice.

Egg. The white eggs are inserted into midrib or leaf sheath in masses of 8-16. Eggs are covered by a dome-shaped egg plug secreted by the female. Red eye spot develop at the head end before the eggs hatch.

Nymph. Nymphs are found near the base of tillers where it is shady and humidity is high. Young nymphs are white, turning brown as they mature. As with leafhopper and planthopper, nymph and adult move laterally like crabs to the opposite side of tillers when disturbed. Nymphs feed on the same tillers in which they hatched and unlike those of other hopper species, can become highly aggregated.

The wing pads of mature nymphs are light brown and opaque; short-winged adults have transparent wings.

Damage

Nymph and adult insert their sucking mouthparts into the plant tissue and remove plant sap from phloem cells. The brown planthopper removes more plant sap than it can digest. The excess plant sap, which is high in sugar, is expelled from the body as honeydew. The honeydew drops fall on the base of plants and in time turn black from infection by a sooty mold fungus.

During the act feeding, the brown planthoppers secrete solid feeding sheaths into the plant tissue to form a feeding tube. The feeding sheaths block the flow of plant sap.

The brown planthopper may remove enough sap or block its flow to cause the tiller to dry and turn brown, producing hopperburn during later growth stage. Hopperburn occurs more rapidly during cloudy weather. Photosynthesis during sunny days allows the plant to recover from sap removal by hoppers.

The brown planthopper also transmits ragged stunt and grassy stunt viruses.

Brown planthopper outbreaks are associated with development of irrigation systems to allow year-round rice cropping (thus continuous planthopper buildup), excessive fertilizer usage results in higher planthopper populations, and the use of insecticides that kill natural enemies.

Plant hosts. The brown planthopper is restricted to rice and wild rices, but reproduction can occur on Leersia hexandra.

Management

Cultural control. Grow no more than two rice crop per year. Crate a rice-free period during the year with early-maturing varieties, plant neighboring field within 3 weeks of each other, and plow down volunteer ratoon after harvest.

Use fertilizer judiciously. Split nitrogen applications three times during crop growth.

To reduce brown planthopper population, drain the field for 3 or 4 days during infestations.

Eliminate virus source in rice and weeds by plowing down stubble.

Plant seedbed in areas as it is possible from light is sources of virus infection. Light attract virus-hatched hopper and weeds is alternative hosts of virus. The virus-carrying hoppers.

Resistant varieties

Planting a resistant variety is effective way of controlling brown planthopper. Brown planthopper numbers decrease on resistant varieties because of the presence of toxic chemicals produced by the plant

Early-maturing varieties to reduce brown planthopper population development.

Higher planthopper population per area occur on high tillering varieties because of the increased plant surface on which to feed.

Biological control

Many parasites, predators, and pathogens attack all stages of the brown planthopper and effectively control this pest under most situations. Improper use of pesticide, however, can kill the natural enemies and thus lead to dramatic brown planthopper outbreaks.

Eggs are parasitized by Anagrus aptabilis (Mymaridae), Paracentrobia andoi (Trichogrammatidae), and Tetratichus formosonus (Uelophid wasps). Cyrtorhinus lividipennis (Miridae) and Amblyseius nr colorai (Phytoseiidae) prey on eggs.

Elenchid strepsipterans, dryinid wasps, and nematodes parasitize nymphs and adults.

Aquatic predators under water surface {Hydrophilus offinis (Hydrophilidae) and Cybister sp (Dytiscidae)} and those that on the surface {(Ranatra dimidiata (Nepidae), Microvelia douglasi atrolineata (Veliidae), Mesovelia vittigera(Mesoveliidae)} prey on hoppers that near the water or fall in the water. Beetles (Microspis crocea, Ophionea ishii) and spider (Callitricia formosana) actively search the foliage for brown planthopper nymphs and adult. Dragon fly (Crocothemis servilia, Agriocnemis femina) prey on moving adults and nymphs.

Fungal pathogens (Beauveria bassiana, Erynia delphacis, Metarhizium anisopliae) infect brown planthopper nymphs and adults. After the death of planthopper, the fungi grow out of the corpses.

Chemical control

Insecticide application

Insecticide to control brown planthopper usually do not necessary in fields to resistant variety.

Apply an effective insecticide on susceptible varieties whenever the brown planthopper population reaches the economic threshold.

Granule are less effective than sprays or dust, particularly when applied to older plants with a greater biomass.

Applying insecticide when the population is mostly young nymphs is useful. Predators normally will lower lower their numbers and young nymphs cannot damage the crop.

Scouting.

Visit the fields weekly from the seedbed to mature grain stage. Pick 20 hills at random across the paddy. Hit each hill several times with the hand and count the number of mature nymphs that fall on the water. Mature nymphs are brown and immature nymphs are white.

Determine the average number of tillers per hill. No action is required until the number of mature nymphs reaches one per tiller. When that occurs, visit the field every 3 to 4 days thereafter. If the population of mature nymphs increase beyond one per tiller, spray the base of the plants.

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.