Kingdom: Animalia

Phylum: Arthropoda

Class: Insecta

Order: Hemiptera

Suborder: Heteroptera

Family: Alydidae

Subfamily: Micrelytrinae

Tribe: Leptocorisini

Genus: Leptocorisa

Species: L. acuta

Leptocorisa acuta has not been found in the U.S. despite the large acreage of rice grown in California, Louisiana and Arkansas. Rice bugs have been found in Australia, Bangladesh, Burma, China, Fiji, India, Indonesia, Malaysia, Papua New Guinea, The Philippines, Thailand and Samoa as well as in several Central American countries. Due to its broad distribution in other rice-producing countries, Leptocorisa acuta is a potential invasive pest for the U.S., but has not yet been reported.

Host Range
These bugs are usually seen feeding on the foliage and flowers of leguminous and graminaceous crops. Leptocorisa acuta (Thunberg) can be found on many crop plants in the family Poaceae (grasses), especially rice. It is also recorded on beans, breadfruit, guava, mango, millet, and more, as a minor pest.

Leptocorisa acuta adults are crepuscular (active during the early morning and late afternoon). After 8-29 days, adults of both sexes are fully mature. Adults may live up to 69 days. Females live longer than males on average: 60 and 48 days, respectively. Rice bugs are most abundant at conditions of 80-82°F and around 80% relative humidity (Pathack and Khanv 1994). Populations tend to increase during the flowering stage of the rice crop, which coincides with warmer weather. Upon adult emergence in the spring, rice bugs feed on wild host plants for one or two generations before migrating into rice fields. It is believed that after the rice is harvested, the bugs overwinter in wild grasses or other grass crops. According to Schaefer and Panizzi (2001), females lay up to 25-87 eggs over their life time. Eggs are deposited in single or double rows of 10 to 20 on the upper surfaces of the leaves of the host plant. Eggs are attached to the leaf by an adhesive substance secreted by the female during oviposition.

According to Corbett (1930), newly emerged nymphs can live for at least 24 hours without food. Although they vary in size, the five nymphal instars are not easily distinguished from one another because of their similarity in appearance.

Leptocorisa acuta, the rice ear bug, shares certain morphological similarities with other insects, especially those belonging to the Alydidae family or other true bug groups. True bugs, including Leptocorisa acuta, typically have an elongated and slender body shape. While Leptocorisa acuta is often brown or gray, coloration can vary. Some other true bugs may also share similar earth-toned coloration, making visual identification based solely on color challenging.

 Its habit of feeding on rice grains during both vegetative and reproductive stages underscores its reliance on the rice plant for sustenance. 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 a prolonged development 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.

Adults: Leptocorisa acuta adults are long (14-17 mm) and slender (3-4 mm wide). They are a light yellow-green to yellow-brown color (Figure 1). The head is broad, often similar in length and width to the pronotum (upper surface of the first plate on the thorax) and the scutellum (triangular shaped plate on the thorax, posterior to the pronotum). These bugs have globular, protruding eyes in addition to small ocelli (simple eyes), which are difficult to see. The fourth antennal segment is curved and longer than the third segment (Corbett 1930).

Adults are usually found in aggregations. Like all true bugs, they have piercing-sucking mouthparts that puncture the substrate they are feeding on, which can damage plant tissue and reduce grain yields. When disturbed, adults emit an unpleasant odor considered to be stronger than the odor emitted by true stink bugs (Pentatomidae). Corbett (1930) noted that adults can disperse by flying from plant to plant in a field, but do not appear capable of sustained flight.

Eggs: Eggs are oval with the tops slightly flattened. Females lay eggs in batches of 10 to 20 in rows on the upper surface of the leaf blade. When they are freshly deposited, eggs are a cream-yellow color, turning to a reddish-brown after approximately one week.

Nymphs: A week following oviposition, the eggs hatch, and within 3-4 hours the nymphs begin feeding (Corbett 1930). There are five wingless nymphal instars with a total nymphal period of 25-30 days. Nymphs are mostly pale yellow-green and have long antennae. Each nymphal instar looks remarkably similar to the one before it, except each successive nymph is larger than the last and wing pad enlargement occurs. Unlike other species in the Alydinae subfamily, the nymphs of Leptocorisa acuta do not mimic ants.

Rice bugs feed by inserting their needlelike mouthparts into new leaves, tender stems and developing grains. Consequently, the plant reacts to repair the tissue and seal the wound. When injuries accumulate, the plant becomes stressed, which can lead to growth retardation of the grains and some grain and plant deformation. Excessive feeding can cause yellow spots on the leaves. This reduces photosynthesis and, in extreme cases, can damage the vascular system of the plant. Puncture holes also serve as points of entry for several plant pathogens, such as the fungus that causes sheath rot disease. The most economically important damage is caused when the adults and nymphs feed on the developing grains. Such damage causes discoloration of the grains, which reduces market quality.

1. Feeding Damage on Rice Grains

2. Discoloration of Grains

3. Empty or Shriveled Grains

4. Presence of Bugs on Rice Plants

5. Reduced Grain Quality

Rice bugs feed by inserting their needlelike mouthparts into new leaves, tender stems and developing grains. Consequently, the plant reacts to repair the tissue and seal the wound. When injuries accumulate, the plant becomes stressed, which can lead to growth retardation of the grains and some grain and plant deformation. Excessive feeding can cause yellow spots on the leaves. This reduces photosynthesis and, in extreme cases, can damage the vascular system of the plant. Puncture holes also serve as points of entry for several plant pathogens, such as the fungus that causes sheath rot disease. The most economically important damage is caused when the adults and nymphs feed on the developing grains. Such damage causes discoloration of the grains, which reduces market quality.

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%.

Remove weeds from fields and surrounding areas to prevent the multiplication of rice bugs during fallow periods.Level fields with even applications of fertilizer and water encourage rice to grow and develop is at the same rate. Planting fields, within a village, at the same time (synchronous planting) also helps reduce rice bug problems.Capturing rice bugs, in the early morning or late afternoon, by net can be effective at low rice bug densities, though labor intensive.Encourage biological control agents: Some wasps, grasshoppers and spiders attack rice bugs or rice bug eggs. Indiscriminate insecticide use disrupts biological control, resulting in pest resurgence.

As a preventive measure, the removal of alternate hosts, especially graminaceous weeds, can prevent rice bug populations from reaching damaging levels. This is because the bug requires a wild host to feed and reproduce upon before moving into the rice field in early spring. The use of late-maturing cultivars can reduce feeding damage from the rice bug, as their activity corresponds with warm weather and the flowering stage of host grasses. Irrigation should be managed to avoid excess humidity. Corbett (1930) indicated that nymphs and adults may be attracted to trap crops of grasses or early-planted rice and the insects can be collected before the flowering of the main crop. Flooding is effective in killing rice bug eggs, as well as driving adults to the tops of the rice plants where they are more easily targeted with pesticides.

The rice bug is susceptible to broad-spectrum insecticides. Keeping high numbers of rice bugs is important as they are the main predators of eggs and nymphs of planthoppers (Nilaparvata lugens and Sogatella furcifera). If rice bugs are destroyed by insecticides, this can lead to a rapid increase in the populations of planthoppers. If the number of nymphs rises to 400-500 per plant, there is a chance that browning and drying of the rice will occur, known as ‘hopperburn’.

Begin scouting the field at pre-flowering and continue daily until the hard dough stage. Count rice bugs in the early morning or late afternoon from 20 hills while walking diagonally across a transplanted field. Adults often fly out of the way before you reach the rice plant, so counts may only reveal immature forms. Direct control may be required if there are more than 10 rice bugs/20 hills. The choice of insecticide depends on many factors such as the application equipment available, cost of the insecticide, experience of the applicator, or presence of fish. The benefits of using an insecticide must be weighed against the risks to health and the environment.

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Corbett GH. 1930. The bionomics and control of Leptocorisa acuta Thunb. with notes on other Leptocorisa spp. in Malaya. Department of Agriculture S.S. & F.M.S. pp. 40-42. Gunawardena NE, Ranatuga PR. 1989. Laboratory and field studies of natural attractant of the rice pest, Leptocorisa acuta (Hemiptera, Coreidae). Tropical Pest Management 35: 210-211.

Hill DS. 2008. Pests of Crops in Warmer Climates and Their Control. Springer. Saxby, United Kingdom. p. 242.

Mitchell PL, Paysen ES, Muckenfuss AE, Schaffer M, Shepard BM. 1999. Natural mortality of leaffooted bug (Hemiptera: Heteroptera: Coreidae) eggs in cowpea. Journal of Agriculture and Urban Entomology 16: 25-36.

Reji G, Chander S. 2007. A degree-day simulation model for the population dynamics of the rice bug, Leptocorisa acuta (Thunb.). Journal of Applied Entomology 132: 646-653. Schaefer CW, Panizzi AR. 2001. Heteroptera of Economic Importance. CRC Press. pp. 321-336.

Pathak MD, Khan ZH. 1994. Insect pests of rice. International Rice Research Institute (IRRI). pp 37-38.

Corbett GH. 1930. The bionomics and control of Leptocorisa acuta Thunb. with notes on other Leptocorisa spp. in Malaya. Department of Agriculture S.S. & F.M.S. pp. 40-42. Gunawardena NE, Ranatuga PR. 1989. Laboratory and field studies of natural attractant of the rice pest, Leptocorisa acuta (Hemiptera, Coreidae). Tropical Pest Management 35: 210-211. Hill DS. 2008. Pests of Crops in Warmer Climates and Their Control. Springer. Saxby, United Kingdom. p. 242.

Mitchell PL, Paysen ES, Muckenfuss AE, Schaffer M, Shepard BM. 1999. Natural mortality of leaffooted bug (Hemiptera: Heteroptera: Coreidae) eggs in cowpea. Journal of Agriculture and Urban Entomology 16: 25-36.

Reji G, Chander S. 2007. A degree-day simulation model for the population dynamics of the rice bug, Leptocorisa acuta (Thunb.). Journal of Applied Entomology 132: 646-653.

Schaefer CW, Panizzi AR. 2001. Heteroptera of Economic Importance. CRC Press. pp. 321-336.

Pathak MD, Khan ZH. 1994. Insect pests of rice. International Rice Research Institute (IRRI). pp 37-38.