Scirpophaga incertulas
Common name: The Yellow Stem Borer or Paddy Borer
Scirpophaga innotata
Common name : The White Rice Borer
Order : Lepidoptera
Family : Pyralididae
Distribution:
All Asian countries, Bangladesh, India, Pakistan, Sri Lanka, through Southeast Asia, Indonesia, Philippines, upto China and South Japan.
Host:
Rice. The insect is monophagous.
The full-grown caterpillar measures 20 mm and is dirty white or greenish yellow, having brown head and pronotum. The adults have a wing span of 25-45 mm and are yellowish white with orange-vellow front wings. The female moth is bigger than the male and has a centrally situated black spot on each of the fore wings. The females have a prominent tuft of brownish yellow silken hairs at the tip of their abdomen.
Life-cycle:
The pest hibernates as a full-grown larva after making silken hibernacula in rice stubbles from November to March. Its activity starts from April and continues breeding till October. The larva pupates sometime in March and moths start emerging in April. The female mate after dusk and lay about 120-150 eggs on the under surface of the leaves in 2-5 clusters of 60-100 eggs each. The eggs are oval, flattened, pearly white covered with yellowish brown hairs of female tuft. Before hatching, they turn black. The incubation period is 6-7 days. Freshly hatched caterpillars bore into the stem from growing points downwards. They disperse from one plant to another after killing the previous one. The larval period is 16-27 days after going through 6 moultings. Before pupation the emergence hole is constructed which is always located above water level and pupates inside the attacked plant. Pupal period is 9-12 days. The total developmental period lasts in 31-46 days. There are 5 broods of this pest in Andhra Pradesh and Tamil Nadu, 3 broods in Bengal and 2 in Orissa where the pest activity is observed throughout the year. In northern parts of the country in Punjab, there are 4-5 generations in a year from April to October.
Damage:
Due to the cropping of paddy throughout the year in southern parts of India, the pest multiplies continuously and shift from one crop to the next. However, in northern India, the pest is serious only in some pockets. The newly hatched larvae after wandering for one or two hours on the plant surface enter the leaf sheath and feed upon the green tissues for two to three days. Then, they bore into the stem near the nodal region. They disperse from one plant to another with the help of silken thread. Its infestation causes drying of central shoot or 'dead-hearts' in young plants and 'white ears' or drying of panicle in older plants.
The life-cycle and damage of an allied species S. innotata (Walker) is almost similar to Sincertulas.
Losses:
Seven species of stem borers occur simultaneously in the rice field, but S. incertulas is the dominant species and most of the losses are due to this pest. The combined yield losses due to the stem borers varies between 3 to 95 per cent in India and 30-70 per cent in Bangladesh in epidemic years. However, the yield losses are below 50 per cent in most of the countries. Percentage of yield losses have been observed greater with high yielding varieties. An average loss of 100-500 kg of paddy per hectare has been reported from Andhra Pradesh. In Orissa, the cumulative loss has been estimated at 44 per cent, with an increase on one per cent incidence of the pest at the earing stage, the yield is reduced by 0.604 per cent.
Control:
Spray 625 ml of phosphamidon 40 SL or 1.4 liters of monocrotophos 36 SL or 2.5 liters of chlorpyriphos 20 EC, in 250 liters of water/ha, three times at 30, 50 and 75 days after transplanting.
Control of insect attacking nursery crop:
Spray 0.04% methyl parathion 50 EC or 0.05% dimethoate 30 EC after 10 days of germination and repeat after 15 days to control various pests. At the time of transplanting (i) clip infested leaves, galls, egg masses etc. and (ii) dip the roots of the seedlings in 0.02% chlorpyriphos 20 EC + 1% urea for 4 hrs before planting.
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