15 Integrated Pest Management of Rice: Ecological Concepts Gary C. Jahn1, James A. Litsinger2, Yolanda Chen1 and Alberto T. Barrion1 1International Rice Research Institute (IRRI), DAPO Box 7777, Metro Manila, Philippines; 21365 Jacobs Place, Dixon, CA 95620, USA fields. Dryland rice is grown without stand- Introduction ing water. Deepwater rice is flooded deeper than 50 cm for 1 month or longer during the Rice is one of the oldest domesticated crops growing season. It does not include reces- and due to its importance as a food crop sion rice (Catling, 1992). humans took it with them when settling in Insect pests have adapted to each of the new areas further removed from flooded major rice ecosystems as well as to new rice river plains extending to the uplands. For varieties, cultural practices, fertilizers and thousands of years, rice, with the excep- pesticides. Among the wide array of rice tion of some dryland systems, was grown in pests, some transferred from wild rice, are monoculture. This traditional, low-yielding, monophagous to Oryza spp. such as yellow rice production system was more sustain- stem borer (YSB), Scirpophaga incertulas able than any other crop in human history (Walker), green leafhopper, Nephotettix vire- (Bray, 1986; von Uexkuell and Beaton, 1992; scens (Distant), brown planthopper (BPH), Reichardt et al., 1998). Rice has morphed Nilaparvata lugens (Stål) and Asian gall into many forms as a result of its domestica- midge, Orseolia oryzae (Wood-Mason). To this tion by humans, initially along the large riv- day, the distribution of gall midge coincides ers of monsoon Asia, where it was selected with the distribution of wild rice varieties. to be tall to tolerate seasonal flooding but For example, neither the gall midge nor its also could survive periods of drought, and wild rice hosts are found in the Philippines. then further up the watershed to fertile val- Other pests are transferred from grasses such leys and finally into mountainous areas. as Chilo and Sesamia stem borers and many The major rice ecosystems are wetland (also species of leaffolders and butterflies [(skip- known as ‘paddy’ or ‘lowland’), dryland (or pers, Parnara guttata (Bremer and Grey) and ‘upland’) and deepwater. Wetland rice is Pelopidas mathias (Fabricius), and green- grown under flooded field conditions, and horned caterpillar, Melanitis leda ismene can be divided into irrigated, rainfed and (Cramer)]. Various species of armyworms, recession rice. Recession rice is grown when Mythimna separata (Walker), and cutworms, rice seedlings are transplanted into reced- Spodoptera litura (Fabricius), attack the ing water such as occurs when a lake dries pre-flooded crop. As the fields flood, more up. Earth embankments, called bunds, to aquatic species enter the ecosystem, such retain standing water surround wetland rice as black bugs, Scotinophara spp., and rice ©CAB International 2006. Ecologically Based Integrated Pest Management (eds O. Koul and G.W. Cuperus) 315 KKouloul CCh15.inddh15.indd 331515 66/9/06/9/06 99:05:50:05:50 PPMM 316 G.C. Jahn et al. caseworm, Nymphula depunctalis (Guenée). Primarily the International Rice Research The larvae of caseworms have gills, thus Institute (IRRI) developed rapid maturing, standing water is required for survival (Lits- photoperiod-insensitive, semi-dwarf rice inger et al., 1994a). Thrips, Stenchaetothrips varieties in the mid-1960s. In most irrigated biformis (Bagnall), and mealybugs, Breven- systems and some rainfed areas, these new nia rehi (Lindinger), thrive in rice during high-yielding varieties (HYVs) enabled a droughts. Thrips numbers are normally held change from the single-season rice culture in check by heavy rainfall (Mochida et al., to two crops per year. This dramatic shift in 1987). Mealybugs tap the rich flows of sol- agriculture was the basis of the Green Revo- uble nitrogen (N) that are available in rice lution in Asia. The more stable irrigated plants under drought stress (Fennah, 1960; systems reduced losses from drought or Jahn, 2004). Rice bugs, Leptocorisa spp., flooding, and the shorter stiffer stems were are one of the few pests that feed directly less likely to lodge (i.e. topple over) when on developing seeds, resulting in reduced N was added. The more nutrient rich crop yields, poor grain quality and lower seed fuelled greater pest populations (stem borers, germination rates (Jahn et al., 2004). planthoppers, leafhoppers and leaffolders) Over time rice became adapted to the particularly under conditions of indiscrimi- more deeply flooded areas near rivers in nate insecticide usage. New pests emerged the deepwater environment. Here rice such as the whorl maggots and lepidopter- crops are first seeded in dry soil before the ous defoliators. In more temperate climates monsoon seasonal flood. The insect pests leaf beetles, Oulema oryzae (Kuwayama), at this stage are the same as in rainfed wet- occurred and the striped stem borer (SSB), land environments, which typically adjoin Chilo suppressalis (Walker), survived over deepwater rice areas (Catling, 1992). Rice winter in dormancy. In Asia, there are hun- elongates with the rising floodwater up to dreds of species of flora and fauna living in several centimeters per day. There are four a typical rice field each season (Way and rice pests that have adapted to these gruell- Heong, 1995; Schoenly et al., 1996). When ing conditions: (i) YSB, (ii) ufra nematode taken to Africa new pests such as the stalk- Aphelenchoides besseyi, (iii) rice hispa eyed fly transferred from wild rice and Dicladispa armigera (Olivier) and (iv) grasses to domestic rice, but local species of rats. Bandicoot rats Bandicota indica and stem borers, leafhoppers, planthoppers, gall B. bengalensis are dominant in the Indian midge and seed bugs filled similar niches as subcontinent with Rattus spp. in South- their Asian cohorts. The stalk-eyed fly’s pre- east Asia. Once fields are flooded popu- ferred habitat appears to be marshes and is lations of leafhoppers, leaf feeders and thus easily adapted to irrigated rice. Fewer planthoppers decline markedly. Floodwa- new pest species emerged when HYVs were ters bring riverine invertebrate pests such introduced to Latin America, but the stan- as crabs and chironomids into rice fields. dard complement of stem borers, planthop- This system also has a close association pers, leafhoppers, water weevils and seed with fish culture providing additional nat- bugs colonized rice fields. ural enemies of insect pests. The photope- As humans moved from the alluvial riod-sensitive cultivars flower during short river valleys to mountainous regions rice was days marking the end of the flood season carried with them. In some extreme cases the so that the crop is harvested in dry condi- wetland systems were replicated as rice ter- tions once again. YSB is highly adapted races in the Himalayas, Indonesia or the Phil- to deepwater rice. Its eggs can withstand ippines. River water was diverted to carve out 2 days of submergence. The larval stage the terraces and irrigate the crop. New pests can be passed inside submerged rice stems appeared under these conditions. At times and before pupation the larva cuts an exit annelid worms attacked young seedlings and hole for the moth to escape, which is sealed were carried by eroded riverbanks because of watertight in silk. When the moth emerges deforestation (Barrion and Litsinger, 1997). it floats to the surface. Rats and mole crickets bore into the terrace KKouloul CCh15.inddh15.indd 331616 66/9/06/9/06 99:05:51:05:51 PPMM Rice 317 walls and became pests by creating leaks rice bugs. As more of the grasslands turn causing the water to drain out. into ploughed agriculture, the severity of As pressure for agricultural land the grassland pests declines and the system increased, mountainous forests were burned stabilizes. Frequent tillage for annual crops, and dibbled rice was planted in its place. In which are planted before or after rice, sup- slash-and-burn agriculture rice is planted presses the soil pests. the first year in the nutrient rich ash. With impending shortages of rice pre- These small plantings attract a menagerie dicted in the 1970s, irrigation systems were of vertebrate pests that dwell in the forest expanded to take advantage of HYVs. In and, depending on the location, can include Asia, a nation’s food requirements are largely rats, birds, wild pigs, squirrels, monkeys, dependent on these rice bowls. Along with elephants and even rhinoceroses. With fur- improved yields came frequent pest epidem- ther logging, forests become smaller, causing ics. Entire crops may be lost to rodents, BPH vertebrate pests to become concentrated and or combinations of pests. To recover from any nearby plantings become overwhelmed. such losses farmers often borrow money to As Sumatran farmers revealed (Fujisaka purchase seeds for replanting. The inter- et al., 1991), such high populations become est on village credit commonly ranges from difficult to control. Damage is most severe 30% to 100% per year. If the same farmer usually near harvest time. The main control requires any additional inputs (e.g. labour, method is the use of dogs and noise mak- fertilizer or pesticides), he or she must bor- ers hung on strings across fields, with family row additional money. If the inputs are not members taking shifts in making noise over made, due to the high cost, the farmer will 24 h as pigs attack by night and monkeys produce less rice and have less income to by day. The larger animals do more damage pay off debts. Pest outbreaks, therefore, can milling around than actually eating the crop. throw farmers into a cycle of poverty from At night pigs, rhinos and elephants bed in which it is difficult to escape (Jahn et al., the fields and trample plants underfoot. 1996, 1999). Over time, agriculture typically causes Fields receiving supplemental water grasslands to replace forest.