Major Insect Pests of Rice in Asia
Control of insects reduces crop losses. At least 10 different kinds of insects can severely damage the rice plant. Experiments in the Philippines show that plots protected from insect damage usually yield 1–3 tons more than those not treated with insecticides (IRRI 1979).
Some insects feed inside the plant; some attack the leaf surface, the roots, the panicles, and other plant parts. Several leafhoppers and planthoppers transmit viral diseases, aside from causing hopperburn in severe infestations. Because insect populations occur in different locations, it is difficult to outline insect control practices that work equally well everywhere. The control measures outlined in this manual are intended to cover most normal growing situations. When unusual problems arise, notify and consult government experts or ask rice specialists assigned in the area for assistance (IRRI 1976).
Major insect pests
Inside (the plant) feeder
Rice stem borers are one of the most destructive groups of insect pests of rice in Asia. Low yield can be expected as they are frequently found attacking the plant from seedling stage to maturity. The larvae are the most destructive as they enter the plant stem immediately after hatching and feed inside. Common names of stem borers are derived from the color of the larvae. Also, the different species are distinguished by the egg mass formation and moth characteristics.
Striped stem borer(Chilo suppressalis Walker)
Larva. The larva has five thin stripes on the back and along the sides. It grows to 17 mm in length. The general color is light brown.
Moth. The moth is dirty brown. Its wings have dark spots arranged laterally near the tip of each wing.
Egg. The egg masses are arranged like scales of fish. The eggs are arranged in a thin elliptical plate which is whitish when newly laid and becomes dark as the eggs get close to hatching. The striped stem borer moth lays its eggs in a mass along the midrib on the upper surface or undersurface of the leaves. The eggs usually hatch in 5 days.
Plant damage. After hatching, the larvae feed a little on the leaf blade and leaf sheath. Then they bore into the stem. The larvae tend to congregate in a few tillers during the early instar periods, then later transfer from one tiller to another. Pupation takes place inside the larval tunnel inside the tiller.
Yellow stem borer(Tryporyza incertulas Walker)
Larva. The larva is slender and yellowish with velvety surface texture; it reaches 17 mm in length.
Moth. The straw-colored moth has a pointed head. The female has a black spot on each of its forewing.
Egg. Individual eggs are round; the egg mass is oblong and covered with soft, silky, brownish hairs. The moth lays eggs in a mass near the tip of the upper surface of the leaves. The eggs hatch in about 9 days.
Plant damage. The larvae enter the stem and are solitary within a tiller, not transferring from one tiller to another, except in cases where the plant is infested during the early stage. Pupation takes place within the larval tunnel, usually near the basal potion of the stem.
Pink stem borer(Sesamia inferens Walker)
Larva. The larva is pink, dark-headed, 25 mm long, 6 mm wide, has a glossy surface texture, and is distinctly seg-mented with two conspicuous posterior appendages. This larva is the largest among the stem borer species.
Moth. The moth is broad-shouldered with a white band along the tip of each wing.
Egg. The eggs are globular, whitish when newly laid, then turn pinkish near hatching time. The moth lay eggs in rows inside the loosened leaf sheath and are most difficult to detect. The eggs hatch within 8 days.
Plant damage. The larvae bore into the stem where they feed as they develop, often transferring to neighboring tillers. When full grown, the larvae come out of their tunnel and pupate between the loosened leaf sheath and stalk, usually near the base of the plant.
White stem borer(Tryporyza innotata Walker)
Larva. The larva is similar to yellow stem borer larva, except that it is creamy white. The distinct dark stripe seen on the back is actually the alimentary canal.
Moth. The adult moth is slender, white, and is similar in appearance to the yellow stem borer, except for its pink abdominal tip, absence of black spot on each wing, and the prominent black antennae. The antennae appear white, as if coated with white scales from the wings.
Egg. The individual egg is round and covered with soft, silky, grayish hairs. Hatching takes place in about 9 days.
Plant damage. They bore and feed inside the rice stem, cutting off the growing part of the plant at the base, thus causing the plant or tiller to die.
This condition, commonly known as deadheart, is indicated by dried onion-like growing points, which occur when the plants are still young. When the attack occurs during flowering, empty whitish panicles (called whitehead) result.
Leaf feeders
Among the leaf-feeding insects, armyworms are about the most destructive group of insects while still in the larval stage. Collectively, the armyworms and cutworms are known for their voraciousness, leaving only the midribs or stalks of plants.
Common armyworm(Pseudaletia uni-puncta Haworth)
Moth. The common armyworm or ear-cutting caterpillar moths are pale brick red to pale brown in color. They have hairy bodies covered with dark specks and patches. They are about 2–3 cm long and have a wingspread of 3–5 cm. The adult moths are nocturnal, strongly attracted to light (phototropic), and are inactive during the day. They mate and lay their eggs usually after dark, during the early evening hours. The male moth lives for about 3 days and the female lives for 7 days. Generally, the males die shortly after mating.
Egg. The female lays its eggs between the leaf sheaths and the stem near the joint of the leaf sheath and the leaf blade. The eggs are deposited in clusters. Each cluster contains several rows of eggs numbering on the average about 100. The range per cluster would vary from 90 to 230 eggs. The eggs within the egg mass are generally covered with a white adhesive substance that fastens them together. They are whitish to pale yellow but become dark as they near hatching. Incubation period averages 7–9 days.
Larva. The freshly hatched larvae have a dull, whitish color with brown black heads. They are 1.8 mm long and 0.35 mm wide. The full-grown larvae are 30–35 mm long and 6–6.5 mm wide. They are usually dark or greenishgray in color. The larvae are nocturnal. They hide under foliage or debris at daytime and feed actively from dusk to dawn. The full-grown larvae crawl down into the soil where they form individual earthen pupal cells. The pupae are light amber at pupation but become dark brown toward the emergence of the moths. The pupal period varies from 9 to 29 days (the average is 16 days).
Plant damage. The armyworms would appear sporadically and suddenly in immense numbers. They inflict severe losses even before they are detected. Frequently, the pests also disappear suddenly. The larvae start eating at the first instar, leaving a skeleton-like leaf blade. The third-instar larvae feed by cutting big holes in the leaves. At the fifth and sixth instars (full grown), the larvae group together and become voracious feeders. The full-grown larvae cut off the rice panicles from the peduncle. This is why they are sometimes called ear-cutting caterpillars.
Rice-swarming caterpillar(Spodoptera mauritia Boisd)
Moth. The rice-swarming caterpillar or rice armyworm insect is a light coffee-brown moth with dark blotches on its wings. The moth is nocturnal and active after dark. During the day, it hides on soil crevices or other cover and is not generally attracted to light.
Egg. The female lays its eggs in a mass on the upper surface of the leaves of rice and other grasses. Each mass con-tains 300 eggs. A single moth lays about two to four egg masses with 90–100% hatchability. Incubation period is from 7 to 9 days. Hatching usually takes place in the morning.
Larva. The swarming caterpillar is probably the most destructive armyworm species. It is particularly destructive during the rainy season, although it may occur year-round in tropical Asia. The larvae are full grown after undergoing five instars in 22 days. The full-grown larva is about 33 mm long and is dark to pale green with dull stripes near the back. When disturbed, they curl into a ring, a characteristic common to all cutworm and armyworm larvae.
Plant damage. The moths prefer to lay their eggs on 4–20-day-old rice seedlings. The insect is essentially a pest of seedlings and crops younger than 25 days old. They appear suddenly in masses and move like an army, destroying crops from field to field. Plants when attacked look as though a herd of cattle had grazed through them.
Common cutworm(Spodoptera litura Fabr.)
Moth. Adult moths are nocturnal; they are active during the night and fly about and feed on nectar of flowers. At daytime, the moths hide in dark covered places.
Egg. The individual egg is pearly white, round, and has a ridged surface. The eggs are laid in clusters on both surfaces of the leaves of various plants. Each egg cluster contains an average of 300 eggs. A single female can lay up to five egg clusters. The egg within a cluster are arranged in rows and piled up to three layers deep. The eggs are covered with short, yellowish-brown hairs from the abdominal tips of the female moths.
Larva. The newly hatched larvae are tiny, measuring about 1 mm long, and are greenish with a cylindrical body. The full-grown larvae are brown or brownish-black with an orange tinge. The abdominal segments have gene-rally two light brownish lateral lines on each side, one above and one below the spiracles. The total larval period varies from 20 to 26 days. The cut-worm attacks almost any crop, destroying rice, millet, tobacco, cabbage, corn, jute, etc.
Plant damage. The young larvae eat entirely the soft leaves of the rice plant and the full-grown larvae are capable of devouring the entire plant. Cutworms cut the base of plants and hide between individual tillers near the soil.
Rice hispa(Hispa armigera)
Rice hispa frequently causes extensive losses to rice crops in India, Bangladesh, Myanmar, Nepal, Sumatra, and southern China. The adult beetles are about 5.5 mm long with spiny body. The female lays its egg singly, near the tip of the leaf blade, generally on the ventral side. The eggs are partially inserted under the epidermis and are covered with a small quantity of dark substance, the average is about 55 eggs per female. The larval and pupal period combined ranges from 11 to 17 days.
Newly hatched larvae dig into the epidermal membranes and feed on the green tissues of the leaves. The tunneling of the larvae between the two epidermal layers results in irregular translucent white patches starting from the point where the eggs were laid near the tip of the leaf and extending toward the base of the leaf blade. Both the adult and the larva feed on the rice plant. The adult beetles cut their way out of the leaf and become external feeders. They scrape the upper surface of the leaf blade, often leaving only the lower epidermis.
The damaged area appears as white streaks parallel to the midrib. Damaged parts turn whitish and finally dry off.
Rice leaffolder(Cnaphalocrocis medinalis)
The rice leaffolder is a minor pest, although at times it becomes serious. Infestation, however, subsides when the plants become older. The adult moth is small (about 8 mm long), brownish gray, and have wavy lines on wings.
The larvae fasten the edges of a leaf together and live inside the folded leaf while eating the leaf tissues. The damaged leaves dry up, giving the infested fields a scorched appearance. Infestation subsides as the plants grow older and new leaves start to come out. It is controlled by natural parasites and by sprays, which control other insects.
Whorl maggot(Hydrellia sp.)
The rice whorl maggots are found extensively in the Philippines and are abundant between 1 week and 2 months after transplanting. The insect gets its name from the fact that it usually infests the central whorl leaf. A whorl is an unopened young leaf of the rice plant.
The maggots or larvae feed on the whorl of the leaf by remaining in the whorl and feeding on the innermost margin of the leaf. The damage is manifested as small chewed discolored areas on young plants. They also feed on the green tissues between the epidermal layers. However, the larvae usually remain outside the leaves, which are transparent when newly hatched or light cream but turn yellowish when they start feeding.
Rice gall midge(Pachydiplosis oryzae)
The adult fly is as big as a mosquito, is nocturnal, and is attracted to light. Females have stout bright red abdomens,but those of males are darker. This is a serious pest in some parts of Thailand, Vietnam, Indonesia, Sri Lanka, India, Nepal, and Africa. The female, either singly or in groups of three to four, lays its eggs near the base of the plants, on the ligules, on the undersurface of the leaf blade, or on the leaf sheath. A single female is capable of laying 100–200 eggs. The larval period lasts from 5 to 20 days.
The newly hatched larvae creep down into the growing points of the tillers and feed on the bud until pupation. This feeding stimulates the leaf sheath to form into an empty tube, similar to an onion leaf and this abnormality is called gall or silver shoot because it is somewhat shiny. The tillers, which form into galls, do not bear grains and are therefore unproductive.
Rice thrips(Thrips oryzae)
Rice thrips are primarily a pest of rice seedlings. Sometimes though, it infests crops at the heading stage. H. aculeatusinfests rice at all stages of growth. Adult thrips are minute, dark-brown, slender-bodied insects. The female lays its eggs in slits in the leaf blade, which it cuts with its saw-like ovipositor.
Damage is caused by nymphs and adults who lacerate the tissues and feed on the plant sap. The feeding causes the formation of yellowish patches or streaks and results in the curling of leaves from the margin to the midrib. The leaf tips dry off and the plants appear to be suffering from water stress. The degree of damage at flowering ranges from unfilled grains to completely empty heads.
Plant-sucking insects
Leafhoppers and planthoppers are tiny insects but are very destructive to rice crops (Heinrichs 1979, IRRI 1976).Their common names are derived from the color and distinctive body marking of the species. When they attack in large numbers, they cause complete drying of the crop called hopperburn.
Generally, the green leafhoppers feed on the upper part of the rice plant, whereas, the brown planthoppers are found at the basal portion. Both insects damage the plants by sucking the sap and plugging the xylem and phloem tissues.
Leafhoppers and planthoppers are also carriers of viral diseases such as tungro, grassy stunt, yellow dwarf, orange leaf, and newly named virus infections.
Common leafhoppers and planthoppers. Green leafhoppers(Nephotettix apicalis Motschulsky)
Green leafhopper(Nephotettix impicticepsIshihara)is green in color and has black spots on the wings. The young green leafhopper may be simply light green with varying color patterns.
Brown planthopper(Nilaparvata lugensStål) has become a serious threat to rice production throughout Asia. The discovery of several biotypes of brown planthopper underscores the seriousness of this pest. Both adults and nymphs are light brown to dark brown. With continuous rice cropping in irrigated conditions, increase in insect population and severe crop losses almost cannot be avoided (author’s experience in Solomon Island). The increase in severity of the damage brought about by these insects seems to be associated with the new technology recommended for HYVs. The biotypes vary not only in their ability to attack different varieties but also in their resistance to different insecticides. When new resistant varieties are planted over a wide area, new brown planthopper biotypes will develop in a short period of 3 years. Therefore, it is important to understand this particular insect and know how new biotypes, races, or strains (De Datta 1981, Heinrich 1979) evolved.
Zigzag leafhopper(Inazuma dorsalisMots-chulsky)is distinguished by a dark zigzag pattern on its back. The nymphs are generally yellowish brown. It is not a very serious pest.
Grain-sucking insects
Several rice bug species infest rice in tropical Asia. However, the most destructive ones belong to the genus Leptocorisa; they are abundant where rainfall is evenly distributed or where irrigation allows continuous cropping.
Rice bug(Leptocorisa sp.)
The adult bug is long, slender, and brownish-green. Both nymphs and adults are difficult to see in the rice fields because their color resembles that of the rice plants. Their presence is detected by the typical rice bug odor. Both adults and nymphs are active during early morning and at dusk. They suck on grains at the soft dough or milk stage by inserting their stylets at the point where the glumes meet. A diffused brown spot caused by the exudation of the sap marks the point of insertion. The panicles in heavily infested fields are erect and contain many light and unfilled grains.
Ladybird beetle(V. crocea and V. discolor)
These beetles are widely distributed. The adults with oval convex bodies are about 3–4 mm long. Their outer wings are either orange or reddish orange. The adults and nymphs prefer to feed on soft-bodied small insects such as leafhoppers, thrips, mealy bugs, and stem borers. In the absence of these insects, the beetles feed on the leaf blades of rice, leaving small chewed areas. They also feed on pollen grains and frequently damage its development.
Economic threshold level
The economic threshold level (ETL) for rice insect pests may be defined as that point in time when yield losses can be expected due to damage inflicted by insects and, as such, control measures are necessary to prevent the situation from happening. It is also that level of pest population per unit area or pest intensity per number of tillers (hills and plants), as well as the measurement of damage to the crop, whereby pest control programs are executed before economic losses occur. The economic treatment threshold (ETT) is that level at which action must be taken to prevent economic damage. If a decision to take a pest control management action is made, time is still sufficient before the economic injury threshold (EIT) is reached (Heinrich 1975).
Integrated insect pest management
The principles and management of integrated pest control are the same for insects, diseases, weeds, and other crop pests. In an integrated management system, realistic economic injury levels (EIL) are used to determine the need for control actions. EIL, as defined by other authors, is that pest population level or pest intensity that produces an incremental reduction in crop value, which is greater than the cost of implementing a pest management action. The ETT is a level at which action must be taken to prevent economic damage, which is somewhat lower in pest intensity than the EIL.
Heinrichs et al. (1979) described the integration of control measures for all rice pests as follows. In the field, different pests, weather, agricultural practices, and the rice plant are interdependent, all linked together in a unit called agrosystem. Because of this interrelationship, control measures directed against one pest or group of pests may affect other pests. Sometimes, complete integration of agronomic practices and control measures for all individual pest species is not possible. The farmer must then decide which pests are not serious.
Cultivars
Short-duration cultivars decrease rat and planthopper populations. Planthoppers are unable to complete as many generations on short-duration cultivars; thus, population may not reach damaging levels. When insect populations are low, the crop grows faster. Incidence of bacterial and fungal diseases decreases because feeding damage on the leaves and stems, which allows entrance of pathogens, is less in insect-resistant varieties. Resistant varieties control the leafhopper and planthopper vectors of rice viruses. Because of fewer prey, the number of biological control agents decreases, but the ratio of insect pests to predators is lower and is thus more favorable on resistant than on susceptible cultivars.
Disease-resistant cultivars decrease the weed population because healthy plants can compete better. But healthy plants and lush growth are also more attractive to insects.
Pesticides
Insecticides reduce most pest populations. Rat damage is less because there are fewer stem borer-infected plants, to which rats are attracted. Controls of insects allow plants to grow better and be more competitive with weeds. Bacterial and fungal diseases are fewer because weed pathogens usually invade insect-damaged plants.
Virus vectors (the hoppers) are generally controlled by insecticides. However, certain insecticides, if improperly applied, will cause an increase in planthopper number, a condition referred to as resurgence. Resurgence of brown planthoppers in areas where certain insecticides are applied appears to be fairly common throughout tropical Asia. With the increase in number of applications of some insecticides, the resurgence ratio increases. This phenomenon should be considered when a pest management approach to control insects is utilized.
As foliar sprays, BPMC, carbophenotion, FMC 27289, perthane, and several others are unlikely to cause brown planthopper resurgence, while methyl parathion, decamethrin, diazinon, fenitrothion, and fenthion are potentially capable of causing resurgence (Aquino et al 1979).
Resistance has been defined as any population within a species normally susceptible to a given insecticide that is no longer controlled by the same insecticide in the area concerned. It could also be defined as the development of an ability in a strain to tolerate doses of a toxicant, which would prove lethal to the majority of individuals in a normal population of the same species. Thus, treatment of the area with an insecticide and a demonstration of the change in effectiveness of the insecticide are prerequisites to claims of resistance (Magalona 1978). He further explained the following generalization and specific resistance phenomenon.
Changing to another chemical
Two requirements should be fulfilled for this to work: 1) dissimilarity of detoxification pathways and 2) dissimilarity of mode of action of the new chemical in relation to those previously employed. Compound groups of chemicals should have different modes of action to be effective as a substitute, but, unlike organophosphates and carbamates, both of which are known to act through inhibition of the enzyme cholinesterase.
Insecticides in rotation
This may involve the use of two, three, or four chemicals in rotation or may involve the use of one for a number of generations followed by the use of a second, then reverting to the first chemical. There are three proposed requirements for the successful use of this technique: 1) the insecticide should be degraded by dissimilar detoxification pathways, 2) the insecticides should have dissimilar modes of action, and 3) the persistence of their lethal residues should not overlap.
Examples:
For a two-compound sequence, if compound 1 is applied at generation 1, the resistance level goes up to generation 2. However, since compound 1 is not applied and is replaced by compound 2 for generations 3 and 4, resistance will go down. The pattern is repeated for generations 5 and 6 using compound 1 and generations 7 and 8 using compound 2. In this sequence, the pest population during the period that compound 1 is not used is kept in check by applying compound 2 at generation 3. The rise and fall of resistance will essentially follow with the use of compound 1 and also of compound 2. In this manner, resistance is avoided at the same time that effective control is achieved.
There are enough references on the resurgence of brown planthoppers and the issue of residue and resistance buildup which need more attention. Most of the above approaches, by themselves alone, may not appear practical and have not been tested under tropical conditions. But the advice is worth noting and, along with agronomic measures, might prove practical in the long run.
Fertilizers
High nitrogen rates generally favor rice pests, and as population increases, biocontrol agents also increase. Rats and insects prefer to attack plants with luxuriant growth, and diseases thrive well on healthy, vigorously growing plants.
Split nitrogen application decreases weed population because majority of the amount applied at one time is used by the rice crop; very little or none is left for the weeds. Fungal diseases and insects also decrease in number because the rice vegetative growth is less rapid, with split application made at transplanting and at panicle initiation.
It is a well-documented fact that increasing nitrogen fertilizer levels results in higher populations of a number of rice insect pests (brown planthoppers, stem borers, gall midge, leaf folders). The cause of the population increase is attributed to several factors: 1) taller plants, 2) larger leaves, 3) softer plant tissues, 4) more tillers per unit area, and 5) more energy in the plants to be harvested by the pests (Litsinger 1979).
Water management
Periodic draining of fields increases rat and weed problems but decreases virus vectors, and consequently, virus disease infection.
Draining the field reduces brown planthopper population, and the crop is less threatened by hopperburn. Thus, farmers often resort to this practice. On the other hand, if sufficient water is available and the bunds (levees) are high, farmers can increase water depth to cover as much of the rice plant as possible to drive brown planthopper adults and nymphs upward for easy control with insecticides. It is difficult to drown insect eggs because they can utilize oxygen in the water to survive (Litsinger 1978).
Planting method
Transplanting has no effects on most pests and biological agents, but it reduces weed problems because of the competitive advantage of transplanted seedlings, which are almost a month old by the time weed seeds germinate.
Low tiller density manipulated by wide spacing, lower seeding rate, low-tillering varieties, low water depth for irrigation, and less fertilizer reduce brown planthopper popula-tions. The low tiller density creates an open rice canopy that allows more air movement above the water surface, thereby decreasing the relative humidity, which is unfavorable to brown planthopper. But low tiller density, on the other hand, favors damage by stem borers. The larger diameter culms (due to better growing conditions of the plants) are more favorable to the development of stem borer larvae.
The low tiller density also allows better control with insecticide sprays through greater penetration to the base of the plant where planthoppers reside. Some people advocate a 5 x 40 cm spacing with the rows oriented parallel to the path of the sun to better utilize sunlight for growth by minimizing mutual shading. This method does not sacrifice the overall plant population and creates a more open canopy to reduce relative humidity, allow weed control, and facilitate spray penetration.
High tiller density has the opposite effect. Brown planthoppers would find the increased humidity and greater plant surface area favorable for oviposition than less crowded planting conditions. Closely spaced plants shade each other earlier, making them more vulnerable to carbohydrate removal by the brown planthopper. High tiller density would have lower stem borer larvae infestation and more tillers would escape damage. Aside from the brown planthopper and virus vectors, high tiller density would also favor bacterial and fungal development. Rat population would increase as there is now better shelter for rodents.
Planting time
Early planting is a cultural method that effectively controls insects. This is true in areas where there is no irrigated dry-season crop and where the insect pest population dramatically declines during off-season. A dry-seeded crop planted at the time of early rains virtually has no pest problems. However, if farmers wait for sufficient water to prepare the land, several months will have passed, giving the pests enough time to undergo several generations of population increase.
Farmers synchronize planting dates in their fields over a large area and thereby reduce the effective time that the crop is exposed to late-season pest population buildup. This method is particularly effective, if farmers can prepare their land quickly. Because of synchronized planting, the invading pest population is diluted over a larger area and would cause less damage to all crops.
Staggered planting for various reasons over a large area allows pest populations to build up over time and can result in severe yield losses on the late-planted crops. Favorable conditions invite disease organisms and rodents to be present and active in destroying the crop.
In terms of insect management, it is desirable to reduce the number of months that host plants are available for pest buildup. This can accomplished by 1) early plowing after the rains begin to eliminate volunteer rice and weeds; 2) synchronous planting over a large area; 3) ‘plowing under’ rice stubble after harvest; and 4) use of early-maturing, pest-resistant, and photoperiod-insensitive varieties.
Cropping pattern
Irrigated multirice cropping allows for nonstop planting and harvesting schedules for six to seven crops per 2-year cycle. Most of the insect pest epidemics characteristic of the past decade have occurred in such crop areas, particularly those with irrigated dry-season crop. Staggered planting, long turnaround time, and volunteer ratooning allow pest populations to sustain themselves year-round.
The key to pest control under this condition is to create a 2–3-month break in the rice cropping cycle over large contiguous areas. Techniques such as synchronous planting, destruction of rice stubbles and ratoons after harvest, and use of early-maturing varieties will minimize pest problems, if carried out over a wide area. The pest cycle can be broken by planting a nonrice crop during the late dry season after two rice crops. This cropping pattern will allow for optimal use of land irrigation water. Use of resistant varieties and insecticide application give only short-term solutions (Litsinger et al 1978).
Stubble management
Plowing is an excellent management practice that controls most pests because it removes the stubbles that serve as their habitat. Burning straw also controls the stem borers hibernating in the stems and the rats hide in the straw. Fungal and bacterial organisms are also destroyed.
While the field is under fallow, the pests subsist on crop residues. It is therefore advisable to destroy the crop residues as soon as possible. Clean also all farm machinery and equipment, especially those used for threshing, drying, and storage.
Trap crop
This technique is used by many farmers. It involves planting a small portion of the field ahead of the main crop to divert pests, which can easily be controlled. This is a common practice if one considers a nursery seedbed to be a trap crop. At this time, farmers remove stem borer egg masses from rice seedlings before transplanting. The seedbed, of course, is not strictly a trap crop because this is where seedlings grow before being transplanted as the main crop.
Litsinger et al. (1978) describes the procedure of setting up a trap crop. The cultural concept of a trap crop has been tested to control brown planthoppers. One-fourth of the total crop area (around the main crop) is planted 20 days earlier to attract more colonizing hoppers to this instead of the main crop. Only the trap crop rows had to be sprayed with an insecticide when hopper number became high, while the control fields without trap crop rows needed only a blanket insecticidal treatment to prevent hopper damage.
In fields with a trap crop, yields were high for the main crop and insecticide cost was lower. In addition, the restricted use of insecticides offered a sanctuary for natural enemies of the pests.
Insecticide recommendations
The interagency insecticide recommendations for irrigated rice in the Philippines are shown below (MAF 1975).
| Common nameof chemical | Target insects | Active ingredients (kg/ha) |
| Granules (G) | ||
| Carbofuran | Whorl maggot, green leafhopper, brown and whitebacked planthopper, stem borer, leaffolder, and rice caseworm | 1.0 |
| Cartap 4 +MIPC5 | Green leafhopper, stem borer | 1.0 |
| Diazinon | green leafhopper, brown and whitebacked planthopper | 1.0 |
| Endosulfan | Stem borer | 1.0 |
| Pentoate 3 +MIPC3 | Green leafhopper, brown planthopper | 1.0 |
| Wettable powder (WP) or soluble powder (SP) | ||
| Carbaryl 853 | Green leafhopper, rice bug, armyworm | 0.75 |
| MIPC 50 WP | Green leafhopper, brown and whitebacked planthopper, rice bug | 0.4 |
| MIMC 50 WP | Green leafhopper, brown and whitebacked planthopper | 0.4 |
| Acephate 75 | Green leafhopper, brown and whitebacked planthopper, rice bug | 0.4 |
| BPMC | Green leafhopper, brown and whitebacked planthopper, leaffolder | 0.4 |
| These insecticides may stimulate an increase in brown planthopper population at the reproductive stage of the crop and should not be applied 40 days after transplanting. |
Major Insect Pests of Rice in Latin And Central America*
Most insects are large enough to be observed, but a few are minute or difficult to detect. These can be identified through their feeding habits. Damage is caused by chewing, sucking, and rasping insects, the first two classes being the most important.
Rice water weevil(Lissorhoptrus oryzophilus)
This is a major pest of flooded rice in many countries. The adult weevils feed on rice leaves, leaving white longitudinal scars parallel to the midrib. The adults measure about 3 mm. Eggs are laid below the water level and the larvae feed on the rice roots. The legless white larvae measure about 6–12 mm in length. When a considerable portion of the root system is destroyed, the older leaves become yellow and the plants may lodge.
Fall armyworm (Spodoptera frugiperda)
This insect is found in all rice-growing regions. The larvae feed on the leaves of young rice plants. They vary in color from light brown to green to almost black and have three yellowish lines on the back that extend from the head to the tip of the abdomen. Two of these lines unite to form an inverted Y on the front part of the head. The larvae of some species feed at night and hide in the soil at daytime. When present in large number, they can defoliate a rice field in a few days.
Rice planthopper (Sogatodes oryzicola)
This small insect has caused tremendous damage to paddy rice. It transmits the hoja blanca virus disease and is often present in sufficient number to destroy entire fields as a result of its feeding. Adults and nymphs suck the sap from the rice leaves and stems and from developing panicles at the booting stage. The insects secrete a honey dew substance, which attracts fungi, causing sooty black spots on the surface of the leaves and stems. The males are smaller and darker than the females, and the nymphs at the immature stage are wingless *Most of the materials are excerpts from Cheany and Jennings (1975) and have two black stripes running the entire length of the body. Resistant varieties are recommended.
Sogatodescubanuscan be distinguished from Soryzicolaby its two black spots on the center back wings. The insect is common in rice fields but feeds more on grasses. It neither transmits the hoja blanca virus to rice nor causes feeding damage.
Rice leaf miner (Hydrelliasp.)
This insect is widespread among flooded rice fields and a number of species are destructive. It usually attacks young seedlings or newly transplanted rice. The adult small fly (3 mm in length) lays an egg on the newly emerging leaf blade; upon hatching, the small larvae tunnel into the leaf blade, leaving longitudinal white scars. By holding the leaf blade against the sun, the small larvae or pupa can be seen. When the whorl of the plant is attacked, it produces white, damaged leaf tip areas that curl like those caused by the white tip nematode.
Stem borer (Diatraea saccharalis)
There are three species of stem borers that seriously attack rice in Latin and Central America. The most damaging and widely distributed is the sugar cane borer, D. saccharalis. The adult moth is seldom seen since it is nocturnal and hides during the day. Eggs are laid on the leaves, and the newly hatched larvae feed on the surface of the leaves for a few days before boring into the leaf sheaths and into the stems. The mature larvae have brown spots on each segment of the abdomen without stripes. When plants are attacked at the early plant growth stage, the growing tip may be destroyed, producing deadheart. Later attacks produce whitehead (empty white panicles).
White stem borer(Rupella albinella)
This is a serious upland rice insect that attacks the plant at the ground level and feeds upward the stem. It is not a serious pest in irrigated rice, even though population is high. Plants attacked by the larvae show yellowing of the lower leaves. After the pupa stage inside the stem is completed, the adult moth exits through a hole.
Stink bugs (Tibraca limbativentris)
These insects are recognized by their shield-shaped bodies and the disagreeable odor given off when they are caught and mashed. Both adults and nymphs can cause damage. The large stink bug,T. limbativentris, is brown and has two small black triangular pits on each side of the front of the scutellum. Early attacks produce deadhearts, while late attack results in whiteheads similar to damage caused by stem borers.
Many species of stink bugs attack the developing grains in the milk or dough stage. Early attacks usually produce empty grains and significantly reduce the yield. Later attacks produce light and chalky grains that break during milling. Stink bug damage can be detected by the presence of brown fungus spots which appear at the point where the grains were pierced by the insect.