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Cut-out areas on leaves (IRRI).
Short-horned grasshoppers, Oriental migratory locust
Oxya hyla intricata (Stal), Locusta migratoria manilensis Meyen
The presence of the insect on the crop and the characteristic form of leaf damage can easily confirm the symptom damage caused by short-horned grasshoppers and locusts.
The symptoms can be confused with the damage caused by other insect defoliators on the rice crop.
Aquatic environments are suitable for the development of short-horned grasshoppers, while locusts may prefer dry environments. Both are favored by the presence of alternate hosts.
The short-horned grasshoppers are common in moist and swampy areas. They are abundant during September and October. The insect pests are nocturnal.
Oriental migratory locusts are commonly found in all rice environments but they are more concentrated in rainfed areas. They predominate the irrigated rice environment surrounded by grassland breeding grounds. Both the adults and the nymphs are nocturnal. They feed on the rice foliage at night. At daytime, they hide at the base of the plant. Under favorable conditions, the adults swarm and migrate.
Short-horned grasshoppers are small to medium and moderately slender insects. They measure from 20-30 mm in length. They are yellow and brown with shiny bodies and with a finely pitted integument. Their eyes are large and close to each other. A broad and brown stripe runs laterally through the eyes and extends posteriorly along the wings. They have short filiform antennae. The antennae of the male are slightly longer than the head and pronotum combined. The female has shorter antennae. Both sexes have fully developed wings. Their wings are green with brownish to bluish bands. They have green and slender hind femora with rounded upper knee lobes and lower knee lobes extended into acute spine-like projections. They have greenish tibiae.
The locust is a large insect with a smooth or finely dotted integument. Its filiform antenna is about as long as the head and pronotum combined. The adults have two forms. The darker adults are those that are bred at high population densities. They have wider heads with almost concave or straight in profile low pronotal crest. They have shorter femur than its wings. The other form of adults came from low population densities. They have a narrow head, high pronotal crest, and long hind femur.
The nymph of short-horned grasshopper is a smaller version of the adult except for the small wing pads.
Neonate nymphs of oriental migratory locust are gray-brown and measure 6 to 10 mm long. Mature nymphs exhibit two colors. At low densities, they are either green or brown. The nymphs are reddish or brownish orange at high densities. Two thin horizontal black stripes are prominent behind the compound eyes. A broader horizontal black band is also located on the lateral sides of the pronotum, on the developing wing pads, and on the dorsal and lateral surfaces of the abdomen.
The eggs of both short-horned grasshopper and oriental migratory locust are in pods. They are capsule-like and yellow to dull reddish brown. With age, they turn darker.
Rice is the primary host of both species.
Short-horned grasshoppers also feeds on maize, sorghum, sugarcane, millet, and Echinochloa spp. Oriental migratory locust also prefers bamboo, banana, beans, betel, cassava, citrus, coconut, cotton, fibers, groundnut, kenaf, kumquat, lablab, legumes, lop buri, maize, market garden produce, millets, nipa palm, phrae, pigeonpea, pineapple, sago palm, soybean, sugarcane, sweet potato, tobacco, wheat, Artemisia sp., Cymbopogon citratus (DC.) Stapf, Dendrocalamus sp., Eragrostis sp., Gigantochloa sp., Imperata spp., Miscanthus sp., Pandanus spp., Panicum spp., Phragmites sp., Polygonum sp., Psophocarpus sp., Saccharum spontaneum L., Themeda gigantea, and Vigna spp. In a laboratory experiment in China, the insect developed on Sorghum sp., Cynodon dactylon (L.) Pers., and Miscanthus sp.
Short-horned grasshoppers and oriental migratory locusts feed on the leaf margins of leaves.
Both the nymphs and adults feed on the leaves and shoots at all growth stages of the rice crop.
Both species are sometimes important pests of the rice crop. The nymphs and adults feed on the leaf by consuming large amounts of leaves. Serious damage caused by short-horned grasshoppers has been reported in Vietnam and China. Oriental migratory locust migrates in swarms and can be highly abundant. Outbreaks of the insect pest usually occur during drought. Records showed outbreaks in China, Philippines, Sabah, and Malaysia.
Among the cultural control options, the following are recommended for short-horned grasshoppers: flooding the stubbles, shaving of bunds, sweeping along the bunds and adults can be picked directly from the foliage at night because they are sluggish. Short-horned grasshoppers and oriental migratory locusts are generally controlled under by natural biological control agents.
Scelionid wasps parasitize the eggs of short-horned grasshopper. Nymphs and adults are hosts of parasitic flies, nematodes, and fungal pathogens. They are also infected by a certain species of an entomophthoralean fungus. Among the predators, birds, frogs, and web-spinning spiders are known.
A platystomatid fly and mite prey on the eggs of oriental migratory locust. Different species of ants feed on the nymphs and adults. They are also prey to birds, bats, field rats, mice, wild pigs, dogs, millipedes, fish, amphibia, reptiles, and monkeys. A fungus also infects the insect pest.
Chemical management includes the use of poison baits from salt water and rice bran. Foliar sprays can also control grashoppers in rice fields. Granules are not effective.
JLA Catindig and KL Heong