Integrated control of yellow rice stem borer Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae)

Abstract

Rice is grown on over 145 million hectares in more than 110 countries in the world. It is staple diet of over half of the world’s population and occupies almost one-fifth of the total world crop land under cereals. Rice crop is also staple food of 2.7 billion peoples in developing countries. Almost 90% of the rice is grown and consumed in Asia. Rice plays an important role in the economy of Pakistan. It is major foreign exchange earner and about 18% of the total foreign exchange is shared by rice. It comes next to wheat as the staple diet and second cash crop next to cotton in Pakistan. Rice is exported around 3.1 million tones earning 1125.82 million US Dollars. The rice crop is subjected to attack by more than hundred species of insect pests in the world. More than seventy species of insect pests have been reported to attack rice crop in Pakistan, of which twenty four species of pests have been commonly observed in Sindh. Among the pests, stem borers are major insect pest of rice crop and responsible for economic crop losses. Twenty one species of stem borers are known to attack rice in the world, of which nine different species have been reported in Pakistan. Among the stem borers, the yellow rice stem borer Scirpophaga incertulas (Walker) is one of the most important to cause colossal losses to rice crop. Globally, S. incertulas alone causes yield losses of 10 million tones. In VIPakistan, more than 90 percent damage was recorded by S. incertulas on rice crop in Pakistan. It is a monophagous insect pest. It attacks rice crop from the seedling stage to harvesting stage and thus can cause complete loss to affected tillers. In Pakistan, insecticides are the main tool to control stem borers. Use of insecticides cause environmental hazards besides various others. Keeping in view the pesticide induced problems; present study was designed to integrate various tactics to control rice stem borers. The efficiency of Neem, Clap-trips and Colocynth Tobacco extracts and chemical insecticide Karate 2.5 EC was investigated against yellow rice stem borer, S. incertulas to restrict pest population. Plant extracts significantly suppressed the population of S. incertulas. The average white heads percentage was noted from 30.63 to 44.77 and 3.72 to 4.00 per cent less in the year 2006 and 2007, respectively in the treated plots than the untreated plot (control). All the treatment including chemical insecticide Karate (standard check) gave the lowest dead hearts and white heads percentage and more numbers of productive tillers and filled grain panicles than the untreated plot (control). The plant extracts have equally controlled S. incertulas as with chemical insecticides. Extracts of Neem, Clap-trips and Colocynth extract produced higher yield than the Tobacco extract and Karate. Maximum number of the different predators were found in neem extract treated plots. On the VIIbasis of tiller infestation, high yield and the number of the predators, neem extract can be recommended as alternative insecticide against insect pest of rice crop. Genetic variability of rice varieties to stem borer attack was significantly observed. Scented rice entries: Lateefy, DR-65, Basmati 385, Basmati 370, Shaheen Basmati, DR-66, DR-61, DR-67, IR67017-13-3-3, PARC-228, Ambreen were noted more susceptible than the coarse rice entries for yellow rice stem borer. The aromatic rice entry Lateefy was recorded moderately resistance to S. incertulas under field and green house conditions than the other aromatic entries. The medium maturing coarse rice entries: Tox 3241-21-3, LTPR-4-32-1-1-1, ITR-344, LT9852-5- 2-1-1, CT22048-3, KAJAT-2, IR86949-1, TCX3162-11-1-2-1, IR65077-33-1-3-3, IR68068-99-1-33, DR-58, IR-6 were comparatively more damaged by yellow rice stem borer as compared to the early maturing rice entries: DR-83XDR-92, DR- 83XDR-46, DR-82XS.Kangani, ZHONG-XIANGI, IR72885-1-4-1-4-3-6, JIANG- ZHOU-XIANGNUD, DR-64 and DR-83. Date of rice transplanting also significantly influenced the stem borer attack. The lowest infestation by S. incertulas was recorded to the 10 th July transplanted crop producing highest yield per hectares. The late transplanting of rice crop in (August) helped in increasing population of S. incertulas, consequently reducing the paddy yield. VIIIHarvesting of paddy at certain levels from soil surface also influence the population of hibernating stem borer larvae. As stubbles height increased larval population of S. incertulas increased. Maximum population of the pest was recorded on stubble height 15 cm. Harvesting of the rice crop should be done 15-20 cm above soil surface. Close harvesting and immediate shifting of harvested paddy will decrease larval population of S. incertulas in stubbles. The rice field should not be left fallow or cultivated without ploughing. Mould Board (MB) plough should be used in rice field for severe larval mortality of S. inertulas. The damage by S. incertulas was observed after fifth week of transplanting. So before fifth week of transplanting application of control measures are not beneficial. Two isolates (274 and 373) with concentration ranging from 10 5 to 10 9 spores/ml of the fungus Beauveria bassiana were tested on eggs, larvae and pupae of S. incertulas. The maximum mortality was noted at higher concentrations (spores/ml). The higher concentrations also reduced egg hatching. The isolate No.274 was more pathogenic than the isolate No.373 to control S. incertulas. B. bassiana has a great potential to control the pest. No effect of B. bassiana was recorded on the predators. IXEating response of the predators (Coccinelid beetle, Carabid beetle, Meadow Grass hopper and Damsel fly) increased as density of eggs and larvae of S. incertulas increased. Among the predators, maximum number of the immature stages of S. incertulas were eaten by Coccinelid beetle. Therefore, we can say that Coccinelid beetle Synhamovia octamaculata is a voracious predator of immature stages. The damsel fly ate significantly less number of eggs and larvae of S. inncertulas than did the other predators. If the damage caused by S. incertulas reaches economic threshold level (ETL), besides other control measures introduction, of the predators will be beneficial for the reduction of pest population. The predators are part of biological control: non hazardous way to keep pest populations under ch