Cnaphalocrocis medinalis, the rice leafroller, is a species of moth of the family Crambidae. It is found in south-east Asia, including Hong Kong, Sri Lanka, Taiwan, Thailand and most of Australia. The wingspan is about 16 mm. The larvae are considered a pest on Zea mays, Oryza sativa and Triticum, Saccharum and Sorghum species. The moth is very active, bright yellow or straw in colour with two distinct wavy lines in the fore wing and one wavy distinct line in the hind wing. It has a wing span of 15mm. Eggs are laid singly or in groups arranged in longitudinal rows on the undersurface of the leaves which are scaly white in color. Fecundity is about 56 eggs. Incubation period is 4–8 days. We find 5–6 larval instars, larval period is about 22–23 days. It pupates with in the infested leaf fold for a period of 6–7 days. The fully grown caterpillar is green in color and is 16.5mm long. The total life cycle completed in about 5 weeks. All the stages of the crop is attacked by this pest. On hatching the newly hatched caterpillar cut the leaf edges and folds the leaf. When young seedlings are attacked it folds 3–4 adjacent plant leaves and scrapes the green matter so that the infested leaves appear white. A single caterpillar damages several leaves. The attacked plants dry up and it reduces the vigour of the plant. Ultimately the yield gets reduced. The yield loss may vary up to 10–50 per cent. It is more problematic at boot leaf stage.
Feature Description
Rice leafroller's egg is close to elliptic, flat shape, about 1 mm long, the first birth is milky white, then become yellow-brown, there will be a black spot before hatching. Larva has 5 instars generally, the larva body length of mature stage is about 15-18 mm. Larva has a brown head, the thorax and abdomen were green at first, then become yellowish-green, and were reddish brown when they were mature. There were two spiral-shaped black lines at the posterior margin of the tergum of the front thorax and 8 distinct small black circles at the tergum of the middle and posterior thorax, among which there were six leading edges and two trailing edges. Pupa, about 9 mm long, abdominal 5th to 7th segment near the leading edge with 1 line of dark brown fine, tail tip, with 8 barbed, pupa long with white thin cocoon. The adult is 7-9 mm long approximately, the wingspan is about 13-18 mm, show flaxen, proala has 3 brown transverse belt, among a relatively coarse short. The central part of the leading edge of the male moth's proala has a shining and concave eyespot, while the female moth's proala has no eyespot.
Pest Impact
Rice leafroller is harmful at the stage of larva. A single larva can consume approximately 25 square centimetre of leaf tissue, constituting less than 40% of a normal leaf of rice. Generally, the 1st-instar larva crawled into the heart leaf or the leaf sheath nearby, and the 2nd-instar larva began to spin silk at the leaf tip, and then began to turn into a small insect bud after the 3rd-instar. The food intake at 4th and 5th instar, which accounting for more than 90% of the total food intake of the larva. Although, there are some differences between different generations. Rice is the most important staple food for more than half of the world population including India. It is grown on an estimated 41.85 million hectares in India with a production of 102 million tonnes. Insect pests inflict an average of 21%–51% yield loss in rice, which leads to one of the major reasons for poorer crop productivity in India. The leaf folder infestation may cause more than 50% of leaf damage with significant yield losses.
Reform the tillage system and cultivation system, rational fertilization, avoid the early growth of rice, late ripening. Also, the damage of rice leaf roller could be reduced by avoiding early, middle and late rice mixed cropping. It is also possible to reduce the damage of pests through variety layout, setting up trapping and killing fields and reducing application area. It is also possible to harvest early rice according to the growth rate of the leaf roller, and then kill some larvae and pupae in deep water, so as to reduce the birth rate of the next generation.
Physical and Mechanical Control
Because rice leaf roller has phototaxis, it has a strong tendency to metal halogen lamp, and farmers can use light to lure and kill pests. Lure insect lamp has the advantage of quick, effective, and simple operation. It rarely requires medicament, and does not cause environmental pollution.
Biological Control
Application of chemical pesticide results in drag resistance and re-occurrence of the pests, and also kills natural enemy of the pests. However, natural enemies can effectively control the pest. It is estimated that there are more than 130 natural enemies of rice leaf roller. Therefore, the protection and utilization of natural enemies is very important to improve the sustainability of rice pest management.
Chemical Control
The selection of pesticides should be based on biological pesticidebacillus thuringiensis, select some high efficiency, low toxicity pesticides. According to different generations, the use of pesticides should be reasonably arranged and used alternately to prevent the resistance of rice leaf roller.
