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WBPH adults (IRRI)
Brown planthopper (BPH), Whitebacked planthopper (WBPH)
Nilaparvata lugens (Stal), Sogatella furcifera (Horvath)
Hopperburn caused by BPH (IRRI)
Hopperburn caused by the planthoppers is distinguished from other hopperburn symptom by the presence of visible sooty molds at the bases of the rice plant. Virus infected plants may also be found.
Hopperburn is similar to the feeding damage or “bugburn” caused by the rice black bug.
The planthoppers are common in rainfed and irrigated wetland environments during the reproductive stage of the rice plant. The nymphs and adults of the insect are usually found at the bases of the canopy, where it is shady and humidity is high.
The adult females are active at temperatures ranging from 10 °C to 32 °C. Macropterous females can survive more than males at varying temperatures. The adults usually live for 10-20 days in the summer and 30-50 days during autumn.
The macropterous forms or the long-winged are more attracted to light trap. The most number of catch occurs during the full moon.
High nitrogen levels and close plant spacing tends to favor both the BPH and WBPH increase. Outbreaks of the insect pests are closely associated with insecticide misuse, especially during the early crop stages. These insecticide sprays usually directed at leaf feeding insects disrupt the natural biological control, which favor the BPH development as secondary pest.
BPH adult is brownish black with yellowish brown body. It has a distinct white band on its mesonotum and dark brown outer sides. The adults exist in two forms, macropterous and brachypterous. Macropterous adults or long-winged have normal front and hind wings, whereas brachypterous forms or the short-winged have reduced hind wings. A prominent tibial spur is present on the third leg.
The nymph has triangular head with a narrow vertex. Its body is creamy white with a pale brown tinge. Mature nymph is 2.99 mm long. It has a prominent median line from the base of the vertex to the end of its metathorax where it is the widest. This line crosses at a right angle to the partition line between the prothorax and mesothorax.
The eggs are crescent-shaped and 0.99 mm long. Newly laid eggs are whitish. They turn darker when about to hatch. Before egg hatching, two distinct spots appear, representing the eyes of the developing nymph. Some of the eggs are united near the base of the flat egg cap and others remain free.
WBPH adult is brownish black with a yellowish brown body. It has very distinct white band on its mesonotum with dark brown outer sides. It has pale yellow to light brown cheeks. The adult exhibits two body forms. The males are all macropterous or long-winged and the females are both macropterous and brachypterous or short-winged. The adult is 2.6-2.9 mm long. The apex of its front wing has an unbranched band. The hind tibia is noticeable because of its distinct movable spur.
Neonate nymph is white to light yellow and 0.8 mm long. It has pink to red eyes. With age, the nymph becomes grayish with white markings on the thorax and abdomen of the creamy body. The mature nymph is 2.1 mm long. A distinct white band on its thorax starts to appear.
Newly laid eggs are creamy white. They are elongate and very curved. A single egg measures 0.9 mm long and 0.2 mm wide. With age, the eggs become darker and develop two distinct spots that represent the eyes of the developing hopper.
Although there are many plants listed as alternate hosts to BPH and WBPH, none of them were able to support a population.
Both the nymphs and adults of the brown planthopper insert their sucking mouthparts into the plant tissue to remove plant sap from phloem cells. During feeding, BPH secretes feeding sheaths into the plant tissue to form feeding tube or feeding sheaths. The removal of plant sap and the blockage of vessels by the feeding tube sheaths cause the tillers to dry and turn brown or a condition called hopperburn.
The planthoppers attack all plant growth stages but the most susceptible stages are from early tillering to flowering or during the first 30 days after seeding until the reproductive stage.
Planthoppers suck the sap of the leaf blades and leaf sheaths. Feeding damage results in the yellowing of the plants. At high population density of the insect pests, hopperburn or complete drying of the plants is observed. At this level, the crop loss may be 100%. In field conditions, plants nearing maturity developed hopperburns if infested with about 400-500 BPH nymphs. In the 1970s and 1980s, BPH was considered a threat to rice production in Asia. Brown planthoppers also transmit ragged stunt and grassy stunt viruses.
It was recorded that at a population density of more than 400-500 nymphs or 200 adults per plant, WBPH can cause complete loss of rice plants. Outbreaks of WBPH were reported in Pakistan in 1978, Malaysia in 1979, and India in 1982, 1984, and 1985. No record shows that WBPH is a vector of any rice virus disease.
There are cultural controls and resistant varieties, which are recommended against BPH.
For example, draining the rice field for 3-4 days is recommended during the early stage of infestation. Nitrogen application can be split to reduce BPH buildup. Synchronous planting within 3 weeks of staggering and maintaining a free-rice period could also decrease the build-up of BPH.
The common parasites of the eggs are the hymenopteran wasps. Eggs are preyed upon by mirid bugs and phytoseiid mites. Both eggs and nymphs are preyed upon by mirid bugs. Nymphs and adults are eaten by general predators, particularly spiders and coccinellid beetles.
Hydrophilid and dytiscid beetles, dragonflies, damselflies, and bugs such as nepid, microveliid, and mesoveliid eat adults and nymphs that fall onto the water surface.
Fungal pathogens also infect brown planthoppers.
There are varieties released by IRRI, which contain genes for BPH resistance, like IR26, IR64, IR36, IR56, and IR72.
BPH is a secondary problem due to insecticide spraying for leaf-feeding insects in the early crop stages. To reduce the risk of hopperburn, application of early season insecticide should be avoided.
WBPH population can be regulated by natural biological control agents. For example, small wasps parasitize the eggs. Predatory mites and mirid feed upon both the eggs and nymphs. Predators for the nymphs and adults are aquatic dytiscid and hydrophilid beetles, immature forms of damselflies and dragonflies, and water-dwelling veliid and mesoveliid bugs. Spiders, stapphylinid and carabid beetles, and lygaeid bugs search the plant for WBPH nymphs and adults.
Nasu S. 1967. Taxonomy, distribution, host range, life cycle and control of rice leafhoppers. In: Major insect pests of rice. Proceeding of a Symposium in the International Rice Research Institute, Philippines, Sept. 1964. Baltimore, Md. (USA): Johns Hopkins Press. p 493-523.
Pathak MD, Khan ZR. 1994. Insect pests of rice. Manila (Philippines): International Rice Research Institute. 89 p.
Philippine Rice Research Institute (PhilRice). 1999. Field guide on harmful and useful organisms in Philippine ricefields. DA-PhilRice Maligaya, Muñoz, Nueva Ecija. 58 p.
Reissig WH, Heinrichs EA, Litsinger JA, Moody K, Fiedler L, Mew TW, Barrion AT. 1986. Illustrated guide to integrated pest management in rice in tropical Asia. Manila (Philippines): International Rice Research Institute. 411 p.
Shepard BM, Barrion AT, Litsinger JA. 1987. Helpful insects, spiders, and pathogens. Manila (Philippines): International Rice Research Institute. 127 p.
JLA Catindig and KL Heong