Agricultural Crop Pests in Southeast Asia Including Southern China
Southeast Asia is often called the Oriental faunal region and includes the provinces of southern China south of the Yangtse river (Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hubei, Hunan, Jiangshu, Jiangxi, Sichuan, Yunnan and Zhejiang) as well as the island of Taiwan, islands and peninsular area of Hong Kong, Macao and those countries to the south including Vietnam, Malaysia, Singapore, Myanmar (Burma), Cambodia and Laos, as well as portions of Pakistan and India. The northern provinces of India share similar faunal elements as southern China as both are at a similar latitude. The insect fauna of northern China is more Palearctic in nature and many of the northern species will diﬀer from those in the southern provinces or elsewhere in Southeast Asia.
Insects of Rice
What are believed to be key pests, or those of major importance as opposed to minor can vary from country to country. In Vietnam and southern China, the rice stemborer complex of lepidopterous insects includes the yellow or small rice borer, Scirpophaga incertulas (Wlk), the striped rice-stalk borer, Chilo suppressalis (Wlk), the darkheaded rice borer, C. polychrysus (Meyr) (all Pyralidae) and the noctuid pink borer, Sesamia inferens (Wlk). Although they are considered minor pests in some regions, because the rice plants are able to tolerate some damage and can compensate for light infestations, these insects have been ranked as major pests in the countries of Malaysia and Thailand. The yellow or small rice borer, Sc. incertulas, has a wide distribution in Southeast Asia and is found in India, Pakistan, Sri Lanka, Bangladesh, Myanmar (Burma), Vietnam, Singapore, Taiwan and Hong Kong.
The common names of these insects generally refer to the color of the larval stage such as the pink borer, S. inferens, with pinkish-colored larvae, or the yellow larvae of the small rice borer. The head capsule in larvae of C. suppressalis is brown in color while larvae of Sc. incertulas are yellow with brown heads and the pink borer caterpillar, Sc. inferens, is pink in color and larger when mature than the other species. The larvae tunnel as caterpillars into the stems of the rice plants. There they feed on the plant tissues and destroy the growing points of the plant causing wilting of new shoots, eventually producing a condition known as "dead heart.“’ In mature plants, empty panicles appear white in color, and the condition is known as “white-head.” Masses of eggs are generally laid on the leaves in the case of the female dark-headed borer or striped rice borer. Pupation generally occurs in the stem with these species. The female pyralid moths in the genus Scirpophaga have a scale tuﬅ at the tip of their abdomens, while female moths in the genus Chilo have no scale tuﬅ at the end of the abdomen. The female Sc. incertulas has a yellow forewing, which is whitish in Sc. nivella.
The eggs of stemborers are oﬅen attacked by the parasitoid wasps Trichogramma sp. (Trichogrammatidae) and Telenomus rowani (Scelionidae). In Malaysia, granular insecticides have been used to control rice stem borers when the incidence in stems (tillers) exceeds l0%, but this practice is not recommended in southern China or in northern Vietnam where the plants are able to tolerate some damage and compensate for injury.
Rice Leafhopper and Planthopper Complex
The rice leafhopper and planthopper complex includes Nephotettix virescens (Dist) and N. nigropictus (Stål), the green rice leafhoppers (Hemiptera: Cicadellidae) and Nilaparvata lugens (Stål) and the brown plant-hopper (Hemiptera: Delphacidae). These leafhoppers are important in Thailand and Malaysia as well as in India and Pakistan, while the planthopper is more widely distributed and is found in southern China, India, Taiwan, Japan and some of the Pacific Islands. The planthopper is unusual in that it is able to migrate between land masses and migrates from East China to Japan annually. This insect also has migrated to Macao (where rice is no longer grown due to urbanization) from mainland China.
Nephotettix virescens is an important vector of two viral diseases in Malaysia. The first disease is similar to yellow dwarf disease and the second is called Tungro disease. Both cause a stunting of plant growth, the first disease a general yellowing and profusion of tillers, while the second causes a reddening of the leaves. Both diseases decrease crop yield.
The eggs of the rice leafhoppers are laid in rows within leaf-sheaths. The five nymphal stages are completed in l7 days in Malaysia. Leafhoppers generally feed on the upper parts of the plant, while the planthopper, Nilaparvata, feeds at the base of the plants near the water line. The brown planthopper is sometimes considered the most serious pest of rice in Asia. They cause a “scorching” of the plants, or a condition known locally as “hopperburn,” when the number of nymphs and adults per clump of rice exceeds 900 or more. The eggs are generally laid in plant tissue. The young resemble the parents except for their smaller size and absence of wings. Five nymphal stages generally require two weeks to develop. Predators can include the staphylinid beetle Paederus fuscipes and the coccinellid beetle Harmonia octomaculata.
In Thailand and Malaysia, another important pest of rice is the rice gall midge, Orseolia oryzae (W.-M.) (Diptera: Cecidomyiidae), which is also found in Pakistan, India, Bangladesh, Sri Lanka and parts of Indonesia as well as in southern China, where it is considered of minor importance. The larvae of the fly feed between the leaf sheaths and, when reaching the apical buds, can lacerate tissue and can cause the formation of a gall known locally as a “silver” or onion shoot. The adults are delicate looking midges, long and brown in color with long legs. Upon hatching, the pale, 1 mm long larva grows to 3 mm and becomes reddish in color. The pupa, when formed, is pinkish and turns red with age. Grassy vegetation near the rice fields is often associated with the presence of the midge.
The rice leaf folder, Cnaphalocrocis medinalis (Gn), (Lepidoptera: Pyralidae), is considered one of the more important pests of rice in southern China as well as in Malaysia and Thailand. It is also found in India, Pakistan, Sri Lanka and Bangladesh. The larvae fold the leaf while feeding and transparent patches form so that the rice plant appears ragged. The adult moths lay eggs on young, 4 to 6-week-old plants or in nursery stock in Malaysia. Early instar caterpillars feed by scraping the epidermis from rice leaves, while later instar caterpillars fold them. The opposite edges of the leaf, or one edge of the leaf, is attached to the midrib by silken threads produced by the larvae. Pupation occurs inside a silken cocoon within the folded leaf. Parasitoid wasps, such as Apanteles opacus (Braconidae) or Temelucha philippinensis (Ichneumonidae), oﬅen keep populations in check in Malaysia.
The lepidopterous armyworm and cutworm complex, including the rice armyworm, Mythimna loreyi (Duponchel), and the rice ear-cutting caterpillar or paddy armyworm, Mythimna separata (Wlk), are important pests in Thailand and southern China. The paddy armyworm affects rice in Pakistan, Sri Lanka, India and Bangladesh. The larvae feed on leaves and stems and can defoliate the plants.
The rice skipper, Parnara guttata (Bremer & Grey) (Lepidoptera: Hesperiidae), was formerly considered a major pest in southern China, but recent mass production and release of parasitic wasps has probably lowered its status to a minor pest. The larvae roll the apical portion of the leaves, web the sides and cut oﬀ the apex, forming long, conspicuous tubes.
Sugar Cane Insects
The lepidopterous sugar cane borer complex in Thailand includes several pyralids including the yellow top or early shoot borer, Chilo infuscatellus (Snellen), the sugar cane stem borer, Chilo sacchariphagus (Bojer), the white top borer, Scirpophaga excerptalis (Walker) and the noctuid sugar cane stalk borer, Sesamia inferens (Wlk).
The larvae of these insects bore into the shoots of sugarcane. As the common name suggests, the larvae of the yellow top or early shoot borer tunnel into the growing shoots of the plant, while the larvae of C. sacchariphagus bore into the stems. The noctuid moth larvae of purple stalk borer, Sesamia inferens, previously discussed as a pest of rice, also aﬀects sugar cane, but sugar cane is not preferred for oviposition as are rice and grasses. The larvae are colored purple to pink dorsally and white ventrally and have a reddishorange head capsule. The adult moth is fawncolored with dark brown streaks on its forewings and whitish hindwings.
In Malaysia, the white sugar cane aphid, Ceratovacuna lanigera Zehntner, a mealybug-like insect (Hemiptera), causes injury. The non-winged females and nymphs are covered by a waxy layer, while the winged adults are bluish-green in color and are not covered with a layer of wax.
Fruit Tree Insects: Mango-Citrus-Banana-Litchi
One of the most important fruit tree insects is considered to be the Oriental fruit fly, Batrocera dorsalis Hendel (Tephritidae). It is found in Hawaii as well as in other Pacific islands and the southeast Asian countries of Thailand and Malaysia where it is a serious mango pest. In southern China, where there are fewer mangoes grown, it is considered a minor pest. In addition to mangoes, the guava and carambola are aﬀected in Malaysia. The larvae or fly maggots feeding inside the skin of the fruit cause it to decay. Female flies puncture the skin of the fruit with their ovipositors, laying several eggs inside. The larvae can hatch in one day and develop through three instars in about a week. When mature, they are able to leave the fruit by “flipping” themselves in the air and dispersing to enter the ground to pupate. Fruits can be protected from these flies by bagging them using paper bags. The use of traps treated with methyl eugenol as an attractant has met with some success, but as only the males are attracted, it is not totally eﬀective as a control.
In Malaysia, a longhorn beetle known as the mango shoot borer, Rhytidodera stimulans (White), tunnels into the young growing shoots of the tree. Eventually it kills the outer branches, which often break oﬀ during subsequent wind storms. In southern China, the citrus long-horn beetle, Anoplophora chinensis (Forst.) (Cerambycidae), is considered one of the most important pests of citrus trees. The larvae of these beetles tunnel under the bark of young trees and sometimes into the heartwood, which can cause the death of the plants. The adult beetles have striking black and white body coloration. Parasitoid wasps have difficulty reaching the larvae that bore into young healthy trees.
Butterflies (Lepidoptera) are not considered to be serious pests of agricultural crops in the northern hemisphere with the exception of the small white, Pieris rapae. However, in the semi and tropical regions of the world, cold climatic conditions are not as severe and the insects often do not have to enter diapause (hibernation), so there can be continuous generations in some regions almost throughout the year. Papilionid butterflies, as well as several species of skippers (Hesperiidae), cause injury to plants because they are able to oviposit in both the spring and the fall.
In Southeast Asia, the lemon or lime butterfly, Papilio demoleus (L.), and another species known by the common names of the common Mormon swallowtail or the white-banded swallowtail, Papilio polytes L., lay their eggs on the undersides of leaves of citrus plants and are considered important in southern China as pests of citrus. Another species, Papilio xuthus L., is also becoming increasingly important, particularly in the Pacific island area. The first instar in these Papilionid butterflies are colored diﬀerently than older larvae, which may be an adaptation that protects them from predators such as birds or lizards. The early stage larva resembles a bird or lizard dropping as it is dark brown in color with white markings that may appear to be unappetizing to the predator. When the caterpillar is older, its color changes to green with grey and white markings. Hand picking the larvae is probably an adequate control in young plants.
The orange spiny whitefly, Aleurocanthus spinifera (Quaintance) (Hemiptera: Aleyrodidae), is an important insect in southern China as well as India, Sri Lanka, Bangladesh, Malaysia and Thailand. The adults are l mm in length and lay eggs on the undersides of leaves. There are three nymphal stages and the third-stage nymph appears blackish in color with waxy secretions on the outer edge of the body so it looks superficially like an insect pupa. Both the nymphs and the adults remove plant nutrients when feeding, and the honeydew produced by the nymphs encourages a sooty mold to grow on the upper surfaces of the leaves and the fruits. Heavy infestations of this insect cause fruit production to fall oﬀ. A parasitic wasp, Eretmocerus serius (Aphelinidae), has been eﬀective in regulating the orange spiny whitefly in Malaysia.
Aphids, such as the black citrus aphid, Toxoptera aurantii (Bayer de Fonscolombe), and the brown citrus aphid, Toxoptera citricida (Kirkaldy), are important in southern China and also range into India, Sri Lanka and Bangladesh.
Fruit-piercing moths, such as Othreis fullonia (Cl.) (Noctuidae), pierce the ripening fruits of citrus, mango, papaya and guava or banana in order to obtain sap. A short, stout proboscis with a barbed tip enables the moth to puncture the skin of the fruit and can permit the entry of plant pathogens such as viruses or secondary rots that can cause premature fruit drop. Fruit-piercing moths are considered of major importance today in southern China. Management of their populations is diﬃcult as the immature of O. fullonia do not feed on citrus trees. Instead, the caterpillars feed on the foliage of the Erythrina species of shade trees. On the Pacific island of Guam, the eggs can be laid on the foliage all year round and the insects are considered to be major pests as they feed on ripe banana, mango, papaya, pomegranate and guava as well as tough-skinned citrus fruits.
On banana plants, there are two species of leaf rollers or banana skippers in Southeast Asia, one of which is Erionota thrax (Hesperiidae), which rolls the banana leaves in Malaysia, Thailand and in southern China. The caterpillars cut and roll strips of banana leaf, then hide in the roll that is held together by silken threads. They emerge at night to feed and are oﬅen covered with a white powdery secretion.
Litchi and Longan Fruit Insects
The litchie stink bug, Tessaratoma papillosa (Drury) (Hemiptera: Tessaratomidae), has been considered the most important pest of litchi (Litchi chinensis) and longan (Euphoria longan) fruit trees in the Guangdong region of southern China, including Hong Kong and Macao as well as Vietnam and Thailand. The adults are mostly brown dorsally and whitish underneath. Immature bugs, more brightly colored than the adults, have red markings dorsally often with a white waxy secretion underneath. Plant sap is taken from the stems of fruit trees. The saliva of the bug can stain the clothing of fruit tree workers. Also, the fluid is extremely irritable if it gets in the eyes. An eﬀective biological control of the litchie stink bug has been developed in southern China by the Guangdong Entomological Institute in which the egg parasitic wasp, Anastatus japonicus (Eupelmidae), has been mass-reared and released to achieve control in the Fujian, Guangdong and Guangzi provinces. Biological control of the litchie stink bug has also been reported from the northern highlands of Thailand.
The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is currently considered among the top 25 most important arthropod pests in southern China. It was the first agricultural pest in Malaysia to be reported resistant to pesticides, and it is also an important pest in Thailand as well as in India. Its distribution has been considered cosmopolitan. Cruciferous plants, such as the cabbages, are aﬀected. The caterpillars penetrate the epidermis of leaves, mining the tissue and making windows or holes in it. The adult is recognized by the pale triangular or diamond-shaped marks seen on the midline of the back when the wings are closed.
The caterpillar is pale green in color, and it wriggles violently when disturbed, sometimes falling oﬀ the edge of the leaf. A microbial insecticide, Bacillus thuringiensis, is eﬀective in the control of the diamondback moth, but farmers in some areas of Malaysia have not accepted it because this method takes longer to kill the caterpillars than other insecticides.
The green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), is a cosmopolitan insect in Southeast Asia that damages developing vegetables, such as potato, sweet potato, tomato and cotton, by their feeding punctures. Three color varieties or subspecies of this insect are recognized in southern China. An all-green form, known as
N. viridula smaragdula, is the most common, accounting for
The small white butterfly, Pieris rapae (L.) (Lepidoptera: Pieridae), along with two other species, is still considered important in southern China and Southeast Asia. The small cabbage butterfly, Pieris canidia (Sparrman), also damages nasturtium. In both species, larvae feed singly in the cabbage heart, make holes in the leaves and cause frass accumulation. The insects are also found in India, Taiwan and the Philippines, and breeding can be continuous with up to eight generations annually, which is not the case in northerly regions, where overwintering occurs in the pupal stage.
The Asian corn borer, Ostrinia furnacalis (Guenee) (Lepidoptera: Pyralidae, Pyraustinae), is more important in the northern countries of Southeast Asia including southern China where corn is grown. The Guangdong Entomological Institute rates it as a highly important pest there. The larvae bore into the stalks and the ears of corn, and can also survive on foxtail millet, Setaria italica, and on Panicum grasses. The eggs are laid in clusters of