Chilo suppressalis
(striped rice stem borer)

This is one of the most important pests of rice in East Asia, India and Indonesia. In East Asia, C. suppressalis occurs together with Chilo hyrax and Chilo christophi. This pest was probably introduced in Spain and Hawaii by humans (Bleszynski, 1970). It is now also present in the Northern Territory of Australia. The species tolerates low to very low temperatures and is therefore present in temperate and subtropical Asia. This low temperature tolerance enables it to adapt to other regions. The fact that C. suppressalis has become established in France, Spain and Portugal indicates the potential for long-distance movements and there would seem to be a real danger that it could be introduced into Africa, or other ecologically favourable areas.

C. suppressalis ranges from Australasia and the Pacific Islands through Asia to Europe (where it was probably accidentally introduced). The map also illustrates the countries where it has been formally recorded (see also CIE, 1977; Waterhouse, 1993). Bleszynski (1970) noted that records of C. suppressalis from Egypt and Israel related to Chilo agamemnon.

The main host plant of C. suppressalis is rice, but it has also been recorded from maize and from many wild hosts, including Panicum miliaceum, Echinochloa spp., Phragmites australis [P. communis], Saccharum fuscum [Sclerostachya fusca], Typha latifolia and Zizania aquatica.

Jepson (1954) reviewed the earlier literature on C. suppressalis; more recent summaries of information include Pathak (1968), Grist and Lever (1969), Litsinger (1977), Kalshoven and Laan (1981), Vreden and Ahmadzabidi (1986), Hill (1987), and Harris (1990). Reissig et al. (1986) include this species in an illustrated guide for rice IPM in tropical Asia. Additional information and references to recent work on C. suppressalis are available in Rice Abstracts and in the International Rice Research Newsletter, reflecting its major importance as a pest of rice.

C. suppressalis is adapted to temperate climatic conditions and larvae survive low winter temperatures in Japan, China and other northern areas. This is in marked contrast to most other species of Chilo, which are restricted to tropical or sub-tropical regions. Adults are nocturnal and become active early in the evening; adults survive for up to a week in field conditions, with females generally living longer than males. Males emerge before females and are attracted to them by pheromones (Nesbitt et al., 1975). Each female lays 100-550 eggs, usually in batches of 60-70 eggs over a period of 3-5 nights. These are laid mainly on the basal halves of leaves and occasionally on leaf sheaths.

After hatching, larvae cluster beneath the leaf sheaths and later enter the stems to feed. Some early larval instars may disperse to other plants by ballooning on extruded silk threads or by floating on leaf fragments. Several larvae may feed together within a single internode of a plant and they live in a moist pulp of chewed plant debris and frass. They pupate within stems, having first prepared an exit hole from which the adult will emerge.

In the tropics, normal development times are: egg (5 to 6 days); larva (30 days); pupa (6 days). The life cycle is completed in 35-60 days; in favourable conditions up to six generations develop in a year, often overlapping where rice cropping is continuous. In colder climates, final instars remain dormant during the winter. The wide range of C. suppressalis, which extends from the tropics to about 40° N, creates substantial variations in the length of development; in northern Asia, development may take more than a year. The availability of hosts and the occurrence of favourable temperatures determine the number of generations in a year and the extent of population build-up. Mortality may be high in years with mild winters and early springs, which result in eggs being laid on small plants that are unable to support larval development. More eggs are laid on lush rice plants, especially those receiving high rates of nitrogenous fertilizer. Chen et al. (1984a, b; 1987), working in China, studied the spatial distribution of larvae in rice fields and developed life tables for field and laboratory populations. Shen (1983), also working in China, has analysed data collected over 15 years in Henan to determine the key factors affecting overwintering populations and has developed equations to predict outbreaks. In Japan, Kanno (1984) studied mating behaviour and Nozato (1987) studied effects of temperature and day length on seasonal development. In Korea, Kim et al. (1988) analysed light-trap catches monitoring population trends from 1966-1987. Ryoo and Lee (1985) studied larval aggregation patterns and Uhm et al. (1986) reported local differences in post-diapause development after overwintering. In the Philippines, where much work has been done at the International Rice Research Institute, Heinrichs et al. (1986) studied population development on traditional and modern rice cultivars.

Many natural enemies have been reported in the literature on C. suppressalis. Of these, parasitic Hymenoptera, carabid beetles, spiders and some pathogens may be of importance in limiting populations. No completely authoritative, definitive list is available and elucidation of the many names that have been applied, especially to parasitic Hymenoptera, requires taxonomic inputs to determine their validity. Grist and Lever (1969) reported that Trichogramma australicum in Indonesia and Mauritius and Trichogramma japonicum in Japan, China and Hawaii effect some control of the eggs, and that larval parasitoids include Cotesia flavipes, Cotesia chilonis, Stenobracon deesae, Trathala flavoorbitalis, Temelucha biguttulatus and Xanthopimpla punctata. An anthocorid, Cardiastethus sp. and various species of carabid have been recorded as predators in Japan and the yellow muscardine fungus, Isaria farinosa, has been one of the most important factors controlling overwintering larvae there. Kalshoven and Laan (1981) reported a Trichogramma species parasitizing almost 100% of egg clusters in Java and noted that the tachinid Sturmiopsis inferens Townsend had been recorded from C. suppressalis in Malaysia and was also present on Chilo in Java. Shepard et al. (1987) have published an illustrated field guide to natural enemies of rice pests, which includes some references to stem borers, and Vreden and Ahmadzabidi (1986) published a good illustrated account of the natural enemies of rice pests in Peninsular Malaysia that includes predators, parasitoids and pathogens of rice stem borers.

Infestations of C. suppressalis in rice crops may be detected by looking for dead hearts in young crops and white heads in older crops. Stems showing symptoms should then be dissected to retrieve larvae and pupae in order to rear adults for positive identification. Reissig et al. (1986) describe scouting methods to detect egg masses of this and other stem borers of rice at tiller elongation and panicle extension, which are the two most vulnerable growth stages.

C. suppressalis resembles many other species of Chilo in external adult and larval characters, but can be distinguished by examination of the male and female genitalia. According to Bleszynski (1970), it is most similar to Chilo niponella and Chilo christophi, but is generally smaller and has a more distinct pattern on the forewings.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Introduction

The literature on control of C. suppressalis is extensive. Grist and Lever (1969) and Litsinger (1977) provided brief summaries of the main methods, but the primary literature should be consulted for details. In many rice-growing areas, C. suppressalis is only one of a number of species of lepidopterous stem borer attacking the crop; the relative importance of these species will influence decisions on control, which must be based on local conditions.

Cultural Control

Carryover of populations of larvae and pupae from one cropping period to the next can be minimized by flooding and harrowing or ploughing to turn in stubble and straw and by destruction of any volunteer rice plants that will provide breeding sites between crops. During the cropping period various measures may be used, depending on local conditions. These include regulation of time of planting to avoid periods of peak adult activity (Rustamani et al., 1995), the use of early-maturing varieties to limit the development period of the pest on the crop, and synchronization of plantings and removal of stems close to the ground at harvest so that the borer larvae and pupae are removed with the straw. Studies on the relationship between transplanting times and N-P-K fertilizers were conducted in Korea for different rice pests. Results showed different levels of infestation, but C. suppressalis was strongly influenced by earlier transplanting times (Ma KyoungChul and Lee SeungChan, 1996). Studies on differences between machine transplanted and direct seeded rice showed no difference in the incidence of the pest, only the moment of transplanting was important (Lee SeungChan and Ma KyoungChul, 1997).

Biological Control

Classical biological control has been attempted by introducing the tachinid Paratheresia claripalpis (from South America) into Malaysia and the ichneumonid Eriborus sinicus from Asia to Hawaii (Grist and Lever, 1969), but the main emphasis in biological control at present is through conservation and enhancement of indigenous natural enemies. The most important of these are parasitic Hymenoptera, some parasitic tachinids, and general predators, such as spiders. Some of these are illustrated in Shepard et al. (1987) and Reissig et al. (1986). A survey was conducted in China to compare parasitism in single rice, double rice and wild rice fields. Not only were there differences between the localities, but also in the species composition. The highest parasitism rate was observed in wild rice fields (Jiang MingXing et al., 1999).

Host-Plant Resistance

Much work has been done over many years, especially in Japan and the Philippines, and is continuing in these and other Asian countries. Some highly resistant varieties are known: for example, TKM 6, Taitung 16, Chianan 2, Su-Yai 20, Szu-Mizo, Yabami Montakhab 55, CV 136 and PTB 10. Semi-dwarf varieties, such as IR 20 and IR 26, are moderately resistant. The latest aspects of biotechnology in the development of insect resistance rice are discussed by Katiyar et al. (1999). Physical factors affecting larval survival include the tightness with which the leaf sheath adheres to the stem, the diameter of the stem and its lumen and the amount of sclerenchymatous tissue present. Plants with a high proportion of sclerenchyma, often associated with ridged stems, are less susceptible to boring by larvae. The presence of high percentages of silica in the stems is also linked to varietal resistance.

Transgenic Plants

Several studies have been conducted on the identification of binding sites in Bacillus thuringiensis (Attathom et al., 1995; Fiuza et al., 1996; Lee MiKyong et al., 1997). Transgenic rice plants showed increased resistance in small-scale field tests (Xu DePing et al., 1996) and similar results were obtained on the laboratory (Mochizuki et al., 1999). A larger scale trial using 2600 trangenic rice plants showed promising results in obtaining insect resistant rice plants (Cheng XiongYing et al., 1998).

Chemical Control

Many chemicals have been used against C. suppressalis and other rice stem borers, but the overuse of chemical insecticides has caused severe pest outbreaks, such as that of the brown planthopper, Nilaparvata lugens, and is now generally considered to be an unsuitable control method. Grist and Lever (1969) reviewed information available up to that date. The use of insect growth regulators is an important development (Nakagawa et al., 1995; Nakagawa, 1996; Shimizu et al., 1997). Tebufenozide (moulting accelerating insecticide) proved to be as efficient as organophosphorous insecticides in Spain and pyrethroids in France. It has the advantage of being low in fish and avian toxicity as well as safe to beneficials. Compatibility with other commonly used herbicides is an added advantage (Mattioda and Jousseaume, 1999). The use of pesticides poses problems in Asia where mulberry trees, which are used for the cultivation of Bombyx mori, are usually planted around rice fields. Insecticides were screened for control of C. suppressalis in rice, but low toxicity to B. mori (Liu GuangJie et al., 1999).

Pheromonal Control

Campion and Nesbitt (1983) reviewed the results of field tests in the Philippines, Korea, Japan, Iran and France and discussed the possibilities of using pheromones against this and other stem borers. They concluded that mass trapping is unlikely to provide satisfactory control, but that the development of mating disruption techniques against C. suppressalis merited further study. Since then, Guo et al. (1992) have reported the use of synthetic pheromone to disrupt mating of this species in a field trial in China. Differences in the monitoring range of sex pheromones were observed by Tsuchida and Ichihashi (1995) in Japan. The range seemed to be narrower in the second flight season than in the first one, probably because of competition between virgin females. Kondo and Tanaka (1995) observed a linear relationship between the total number of catches using pheromone traps and the proportion of injured rice plant stems. Thus, it appeared that rice plant damage could be estimated using pheromone trap catches. A more detailed threshold was worked out by Kojima et al. (1996).

Integrated Pest Management

This is now the preferred method of control for pests of rice. Teng (1994) recorded that large-scale implementation of rice IPM was stimulated in the 1970s in several Asian countries by pest resurgences resulting from the indiscriminate use of insecticides. Five countries have now enacted legislation to support IPM. The inter-country programme of FAO, the UN, IRRI and national services is developing implementation, which is based on host-plant resistance, location-specific cultural practices and conservation of natural enemies.

Phytosanitary Measures

Formal phytosanitary measures against this species have not been formulated, but general phytosanitary measures should be implemented to limit the possible spread of eggs, larvae or pupae on infested plant material. The fact that C. suppressalis has become established in France, Spain and Portugal indicates the potential for long-distance movements and there would seem to be a real danger that it could be introduced into Africa, or other ecologically favourable areas.

This is a typical pest species with the ability to invade other rice growing areas with the same or similar temperature and humidity characteristics. Unfortunately there is very little information on these aspects in the current literature. Literature is mostly based on pest control and resistance, but not on distribution, or identification of specimens collected in areas outside the current distribution. The lack of taxonomists for identification will prove a serious obstacle for having more information on distribution.

Bangladesh: International Rice Research Institution (IRRI), House-30H, Road-10B, Banani, Dhaka-1213, Dhaka, Bangladesh, http://www.irri.org

22/11/2007 Updated by:

Koen Maes, Consultant, Belgium