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Rice bug adult (IRRI)
Leptocorisa oratorius (Fabricius), L. chinensis (Dallas), L. acuta (Thunberg)
Damaged grains caused by rice bug (IRRI)
The presence of the insect can be easily determined by an offensive smell. The grains are small, shrivelled, spotty, or deformed. Some grains are also empty.
The symptoms can be confused with the damage caused by nutrient deficiency or flower thrips.
High rice bug populations are brought about by factors such as nearby woodlands, extensive weedy areas near rice fields, wild grasses near canals, and staggered rice planting. The insect also becomes active when the moonsoonal rains begin. Warm weather, overcast skies, and frequent drizzles favor its population buildup.
The population of the rice bug increases at the end of the rainy season.
Rice bugs are found in all rice environments. They are more common in rainfed and upland rice and prefer the flowering to milky stages of the rice crop. Adults are active during the late afternoon and early morning. Under bright sunlight, they hide in grassy areas. They are less active during the dry season. In cooler areas, the adults undergo aestivation or diapause in grasses. They feed on wild hosts for one to two generations before migrating into the rice fields at the flowering stages. The nymphs are found on the rice plant where they blend with the foliage. There, they are often left unnoticed. When disturbed, the nymphs drop to the lower part of the plants and the adults fly within a short distance.
The adults of the three species of rice bugs are slender and brown-green. They measure 19-16 mm long. They have long legs and antennae. Distinct ventrolateral spots on the abdomen are either present or absent.
The younger instars are pale in color. The nymphs have long antennae. The older instars measure 1.8-6.2 mm long. They are yellowish green.
The eggs are oval, shiny, and reddish brown. They are laid in batches of 10-20 in one to three rows along the midrib on the upper surface of the leaf.
Its main hosts are rice and Echinochloa sp. It also feeds on Alloteropsis cimicina (L.) Stapf, Artocarpus sp. (breadfruit), Bothriochloa pertusa (L.) A. Camus, Brachiaria miliiformis (Presl) A. Chase, B. mutica (Forssk.) Stapf, Camellia sinensis (L.) O. Ktze. (tea), Chloris barbata Sw., Dactyloctenium aegyptium (L.) Willd., Dicanthelium clandestinum L., Eleusine indica (L.) Gaertn., Mangifera indica L. (mango), Myristica sp. (nutmeg), Panicum miliaceum L. (millet), P. repens L., Paspalidium punctatum (Burm.) A. Camus, Phaseolus sp. (beans), P. maximum Jacq., Psidium guajava L. (guava), and Setaria glauca (L.) R. Br.
Both adults and nymphs insert their needlelike mouthparts between the lemma and palea of the rice hull to suck the endosperm of rice grain. In order to feed, they secrete a liquid to form a stylet sheath that hardened around the point of feeding and holds the mouthparts in place.
The rice bug is an important insect pest during the milky stage of the rice plant. Both the nymphs and adults prefer the endosperm of the rice grain resulting to production of smaller grains. They also feed during the soft or dough stages and can cause grain discoloration.
Both the adults and nymphs feed on grains at the milking stage. They can be serious pests of rice and sometimes reduce yield by as much as 30%.
The rice bug population can be managed using different cultural control measures and biological control agents.
Cultural control measures include the removal of alternate hosts such as grasses on bunds, early planting, and the use of late-maturing cultivars. Netting and handpicking the bugs reduce their numbers. Likewise, putting attractants such as arasan or anything with an odor like dead snails or rats can easily capture rice bugs in the field.
Among the biological control agents, small wasps parasitize the eggs and the meadow grasshoppers prey on them. Both the adults and nymphs are preys to spiders, coccinellid beetles and dragonflies. A fungus infects both nymphs and adults.
Coarse-grain and bearded cultivars may be resistant to the rice bugs.
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JLA Catindig and KL Heong