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Plantwise Technical Factsheet

yellow stem borer (Scirpophaga incertulas)

Host plants / species affected
Oryza sativa (rice)
List of symptoms/signs
Leaves  -  abnormal colours
Leaves  -  internal feeding
Leaves  -  wilting
Stems  -  internal feeding
Whole plant  -  dead heart
Whole plant  -  dwarfing
Symptoms
After hatching, neonates of S. incertulas bore into the leaf sheath and may cause longitudinal yellowish-white patches as a result of feeding. The larvae usually spend little time in the leaf sheath and bore into the stem, where they stay in the pith and feed on the inner surface of the stem wall. Larvae move from one internode to another by making a hole through the septa. Frequent larval feeding does not cause visible symptoms (Catling and Islam, 1987; Islam, 1990).

Severe feeding damage near the growing point or above and/or a deep circular cut through the parenchyma tissue causes deadhearts at the vegetative stages and whiteheads at the reproductive stages. In the case of deadhearts, the central leaf whorl does not unfold, turns brownish and dries out, and the affected tiller does not bear a panicle. In the case of whiteheads, either growing panicles do not emerge ('hidden whiteheads', Islam, 1990b) or emerged panicles remain empty and white. In both cases, deadheart and whitehead, lower leaves remain green. These symptoms of damage in deepwater rice usually occur before flooding and after flood recession. Damage at the elongation stage usually does not produce such symptoms but affects plant elongation capability resulting in the loss of stems in the rising flood water (Islam, 1990a).

Rice plants are able to compensate for stem borer damage to some extent by producing extra tillers and in some cases by redirecting nutrients from the damaged tillers to the healthy ones. In general, compensation is greater when damage takes place at early growth stages than at the late stages. Rice plants can compensate for, on average, about 23% of whiteheads, which is strongly influenced by physical factors (Islam and Karim, 1997). Plants can compensate about 1 whitehead per hill but suffer yield losses when >1 tiller per hill is damaged. Damage in the reproductive stages is compensated by conversion of some of the unproductive tillers to productive tillers, producing more and heavier grains (Rubia et al., 1989; Islam, 1990; Islam and Karim, 1997). Plants fully compensate deadheart damage at the vegetative stages by the production of additional effective tillers, but these compensatory tillers bore smaller panicles thus suffer yield losses.
Prevention and control
S. incertulas is considered to be the most chronic and serious insect pest in most of the rice-growing countries in Asia. Insecticides are the commonly adopted technique used against this pest. Recent studies indicate that most of the cases of insecticide use against stem borers involve misuse. Farmer's perceive benefits from insecticide use, directly related to farmer's insecticide use and perceived severity, which is guided by the worst attacks (Heong and Escalada, 1999). So far, huge amount of information has been generated on S. incertulas including biology and behaviour, population dynamics, pest and plant interaction, and the role of natural enemies. Based on the available ecological information and effectiveness of different control options integrated pest management (IPM) strategies for S. incertulas may be developed.
Host-Plant Resistance

More than 39,000 varieties of rice have been screened against S. incertulas at the International Rice Research Institute in Laguna, Philippines (Khan et al., 1991), and many national agricultural research systems screened hundreds of cultivars and breeding lines. Resistance in number of varieties or lines has been detected but high levels of resistance are not found in cultivated rice. ASD16, ASD20, Birsa Dhan 201, Chandina, Chianan 2, Co45, CR 712-3-38, IR36, IR72, IRSA69, IRSA76, Majhera 7, Paichung 16, Ptb 10, Ratna, Su Yai 20, TKM 6, TNAU90012, TNAU90094 and WC1263 were moderately resistant to S. incertulas (Khan et al., 1991; Mishra et al., 1996; Ramaraju and Velusamy, 1997; Shanmugasundaram et al., 1997; Singh and Pandey, 1997; Singh et al., 1996). However, several wild rice species have been identified with high levels of resistance which is polygenic in nature. Attempts to upgrade the level of S. incertulas resistance in cultivated rice is an active area of research.

The recent development of transformation techniques has provided the technology for incorporating the bacterial gene lethal to stem borer larvae into rice genome opened a new dimension for the development of pest resistant varieties. Genetic engineering of rice with toxins from Bacillus thuringiensis is being pursued by numerous research groups, and S. incertulas is a major target of this work (Bottrell et al., 1992). The Cry1Aa, Cry1Ab, Cry1Ac and Cry2A proteins of Bacillus thuringiensis are highly toxic to S. incertulas (Alam et al., 1999; Maqbool et al., 1998; Cheng et al., 1998; Datta et al., 1998; Alam et al., 1998; Ghareyazie et al., 1997; Nayak et al., 1997; Wunn et al., 1996). Transgenic rice developed by transformation of rice plants by particle bombardment with a truncated version of one or more of these synthetic genes from Bacillus thuringiensis are highly lethal to S. incertulas larvae. However, the development of a transgenic rice variety and its adoption in the farmer's field is still a debatable issue.

Biological Control

A large complex of natural enemies (>100 species) are associated with S. incertulas but most occur at low levels (Khan et al., 1991). The most vulnerable stages are the adults, eggs and neonates. Up to 99% of the eggs laid fail to survive to adulthood (Islam, 1995b) and natural enemies play a significant role; egg parasitism is high and widespread. The three most common genera of egg parasitoids are Telenomus, Tetrastichus and Trichogramma. Egg predation is usually low except in localized areas where long-horned grasshopper, Conocephalus longipennis, is the major predator. Larvae and pupae inside the rice stem suffer low mortality (Islam, 1992) while young larvae may suffer very high predation before penetration into the rice plant. Several species of hymenopterous parasitoids, fungi, bacteria, viruses and mermithid nematodes also attack the larvae. Studies on adult mortality are scanty. Moths are usually attacked by spiders, dragonflies, birds, etc. Conservation of these natural enemies is essential in order to maximize natural biological control.

Cultural Control

Some cultural practices may have a profound effect on S. incertulas. Some of these are only effective if carried out on a collective basis over a large area, while others are effective in a single field (Khan et al., 1991; Pathak and Khan, 1994). Rice varieties with short stature and shorter growth duration suffer less damage from S. incertulas than tall, long growth duration varieties. Planting or seeding times may be delayed to avoid the peak emergence of moths from the diapausing population, but fields planted later than neighbouring fields may suffer high late season damage. Rice seedbeds may be used as a trap crop for moths emerging from diapause; moths may be collected by sweep nets and egg masses may be collected by hand or leaf clipping. Thorough tillage followed by flooding after harvest may severely reduce the population of S. incertulas, resulting in low incidence in the next crop. The use of sex pheromone may also reduce the borer population (Ganeswara Rao et al., 1994).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Impact
Introduction

Yellow stem borer is one of the major or most destructive/serious pests of rice in Bangladesh (Catling and Alam, 1977), India (Walker, 1975; Panda et al., 1976), Malaysia (Rothschild, 1971; Aziz et al., 1978; Chang, 1981), Myanmar, Pakistan (Moiz and Rizvi, 1971), Philippines (Litsinger et al., 1987), Sri Lanka (Fernando, 1967), Thailand (Yasumatsu, 1976), Vietnam and Indonesia (Pathak and Khan, 1994). It is also a predominant species in Taiwan, south Japan, south China and south Nepal.

S. incertulas is a chronic pest. It is present in almost every rice field in each rice season in areas where it occurs. It is a k-strategy pest, whose moths and young larvae disperse to avoid crowding effects (Islam, 1994). The unique larval feeding damage may cause death of the central leaf whorl at the vegetative stage, which is known as deadheart. Damage at the reproductive stage may cause death of the emerging panicle at the reproductive stage, which is known as whitehead. A large proportion of damaged rice tillers do not show visible damage (Islam and Karim, 1997). Rice plants compensate deadheart damage by the production of additional tillers but suffer yield losses due to compensatory tillers bearing smaller or lighter panicles. Panicle density can also be reduced in the case of heavy attack (Islam, 1990; Islam and Karin, 1999). Plants respond to whitehead damage by reallocation of assimilates from damaged tillers to the healthy ones (Rubia et al., 1996) yet suffer greater losses than the deadhearts. Yield losses are a result of panicle density reduction. Such compensations are influenced by variety, weather, soil fertility and soil moisture conditions, and average compensation was estimated at 23% for whiteheads in Bangladesh (Islam and Karim, 1997). Therefore, even at a very low level of whitehead damage crops suffer some yield losses. Some whiteheads remain enclosed in the leaf sheath and thus remain undetected (Islam, 1990; Islam and Karim, 1997). Stem borer damage in tillers not showing deadheart or whitehead, can reduce filled grain number and individual grain weight, increase sterility (Islam and Karim, 1997), and reduce the elongation ability of deepwater rice which ultimately reduces panicle numbers (Islam, 1990).

Rice plants suffer yield losses due to stem borer damage because it damages the critical plant parts, the panicle or central leaf whorl. As plants can compensate damage to some extent, yield losses are always less than the level of deadhearts and whiteheads (Islam and Karim, 1997, 1999). As a chronic K-strategy pest, S. incertulas has a high potential to cause significant yield losses due to its characteristic damage which directly affects yield components such as panicle numbers, panicle size and weight, grain numbers/panicle and individual grain weight (Islam, 1990; Islam and Karim, 1997, 1999).

Relationship Between Damage Levels and Yield Loss

Attempts have been made to determine the relationship between stem borer damage and yield loss. In most cases, the estimated losses were greater than the damage (deadheart or whitehead) level, ignoring plant compensation. Wyatt (1957) reported that a 1% increase in stem borer infestation decreased yield by 1.3% in Malaysia. Based on data from Cuttak, India, Israel and Abraham (1967) reported that a 1% increase in stem borer damage caused 0.28% yield loss at the vegetative stage and 0.62% yield loss at the reproductive stage. Based on the IRRI data they showed that a 1% increase in deadhearts caused 1.6% yield loss, and a 1% increase in whiteheads caused 2.2% yield loss. In Bangladesh, Catling et al. (1978) found a relationship between deadheart level caused by S. incertulas and grain yield (Grain yield = 100 - 11.6 x log % deadhearts). Gangwar et al. (1986) developed a relationship based on survey data for dwarf (yield (t/ha) = 4.947 - 0.289 x % deadhearts) and tall varieties (yield (t/ha) = 3.354 - 0.122 x % deadhearts).

Micro plot experiments in Thailand (Sindhusake, 1994) indicated that one infested tiller at 49, 56 and 63 days after transplanting (DAT) could reduce grain yield by 4.6, 6.0 and 8.3%, respectively. Results also indicated that the extent of yield loss not only depended on damage levels but also on crop growth stage and environment.

Extent of yield losses

Wide variations in the reported yield losses due to S. incertulas and other stem borer complexes have been observed. Many of these reported yield loss estimates appear to be extremely high. In Bangladesh, stem borers cause 0.3% to 70% yield losses (Alam, 1967; Alam et al., 1972; Catling et al., 1978; Islam and Karim, 1997). The reported yield losses in different areas of India vary from 3 to 95% (Ghose et al., 1960; Israel and Abraham, 1967; Saivaraj and Venugopal, 1979; Nigan and Verma, 1985; Rai and Naidu, 1987). Losses of up to 95% have been reported in Indonesia (Soenardi, 1967), Korea (7%) (Paik, 1967), Malaysia (4-70%) (Wyatt, 1957). In Pakistan, losses of 2-10% in a normal year and up to 100% in an outbreak situation have been reported (Mioz, 1967; Haq, 1970; Koehler, 1970; Ahmed, 1984). In the Philippines, losses of 5-10% in a normal year and up 48% in an outbreak situation have been reported (Rowan, 1923; Cendana and Calora, 1967; Gomez and Barnado, 1974; Litsinger et al., 1987). Losses of 10-30% in Taiwan (Walker, 1975), and up to 15% in the United Arab Republic (El Nahal et al., 1971) have also been reported. Yellow stem borer appears to be well adapted to the aquatic environment of deepwater rice and is reported to cause an annual average yield loss of about 17-20% in Bangladesh and Thailand (Catling et al., 1987; Islam, 1990).

Economic Impact

It is very difficult to quantify the economic impact of rice stem borers including S. incertulas. The incidence of S. incertulas varies between fields, locations, seasons and years (Islam and Karim, 1997). Most of the reported estimates are time and space specific, so extrapolations of such data do not reveal losses in national or geographic locations. The situation is made more complicated by the fact that many estimates were probably made in outbreak situations, which overemphasized the actual losses. Litsinger et al. (1987) estimated an average loss of 18.3% in several locations over a 10 year period from 1976 in Laguna province of the Philippines.

Joint occurrence of more than one stem borer species in a rice field is a common phenomenon, though one species may be dominant. Most of the yield loss estimates seldom report losses due to S. incertulas alone, but rather due to a complex of stem borers. Further more, many of the estimates were based on insecticidal controls, thus losses were combined losses from a number of insect pests, though one or more stem borer might be dominant. Therefore, these estimates report a higher rate of yield losses than the actual losses due to S. incertulas. Estimates based on yield difference in damaged and undamaged plants, and adjusted with the damaged plant intensity provides a loss estimate close to actual losses (Islam and Karim, 1997). Such estimates are rare and not sufficiently covered over large areas. In addition, the majority of the reported estimates tend to ignore the plant's ability to compensate for stem borer damages. Thus most of the estimates are much above the actual loss caused.

However, Savary et al. (2000) recently developed an experimental yield loss database from 445 plots in which they manipulated levels of pest injuries, under cropping practices corresponding to particular production situations and attainable yields. Using the experimental database and the survey data of pest incidence in farmer's fields, they derived estimates of pest induced yield losses for Tropical Asia. They estimated that yield loss due to the most important insect pests of rice, the stem borers, is about 2.3% due to damage at the reproductive stage causing whitehead. Islam (1990) reported that some whiteheads remain enclosed within the leaf sheath and thus overlooked. Side-by-side, stem borer damage at the vegetative stage causing more than 20% deadhearts causes significant yield losses mainly due to compensatory rice tillers bearing lighter or smaller panicles (Islam and Karim, 1999). Stem borer damage in many cases does not cause typical damage symptoms of deadheart and whitehead, but bore the panicle. Such damage may cause yield loss depending on the position, length, intensity and nature of stem damage (Islam and Karim, 1997). This is more common in deepwater rice, which may affect filled grain numbers and individual grain weight (Islam, 1990). If all these loss mechanisms are considered, losses due to stem borers may mount to ca 3-3.5%. In 1999-2000, tropical and sub-tropical Asia produced about 500 million tons of paddy (Mbabaali 2000). At this production level, 3 and 3.5% loss would be 15 and 17.5 million tons. At the present market price (US$ 250/ton) the annual losses due to stem borers could be 3750 to 4375 million US dollars. Among the stem borers, S. incertulas and striped stem borer are the most dominant species in Asia, while white stem borer is important in some countries such as Indonesia. It would not be unjustified if about one third of the total losses caused by stem borers is attributed to S. incertulas. Therefore, the economic value of losses caused by S. incertulas could be around 5.0 to 5.8 million tons, which would be worth about US$ 1250 to 1458 million.


Related treatment support
Plantwise Factsheets for Farmers
Shrestha, T. K.; CABI, 2012, English language
Chandramohan, C.; Ingle, S. R.; Murthy, R.; CABI, 2010, English language
Chandramohan, C.; Ingle, S. R.; Murthy, R.; CABI, 2010, Kannada language
Cambodia, General Directorate of Agriculture (GDA); CABI, 2013, English language
Cambodia, General Directorate of Agriculture (GDA); CABI, 2013, Cambodian language
 
Pest Management Decision Guides
Myanmar, Plant Protection Division; CABI, 2014, English language
Cambodia, General Directorate of Agriculture; CABI, 2014, English language
Cambodia, General Directorate of Agriculture; CABI, 2014, Cambodian language
Chandrasena, G. D. S. N.; Nimalananda, N. P. H.; CABI, 2015, English language
Thailand, Bureau of Rice Research and Development, Rice Department; CABI, 2013, English language
 
External factsheets
IRRI Rice Factsheets: Crop Health, International Rice Research Institute (IRRI), English language
Rice Insect and Pest Control Management Factsheets, Bangladesh Rice Research Institute (BRRI), Bengali language
Bayer CropScience Crop Compendium, Bayer CropScience, English language
IRRI Factsheets, International Rice Research Institute (IRRI), English language
PlantVillage disease guide, PlantVillage, English language
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