Rice leaffolder

Description

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 millimetres (5⁄8 in). The larvae are considered a pest of Oryza sativa, Zea mays, 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 15 millimetres (19⁄32 in). Eggs are laid singularly 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 16.5 millimetres (21⁄32 in) long. The total life cycle completed in about 5 weeks. All the stages of the crop are 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. The rice leafroller's egg is close to elliptic, flat shape, about 1 millimetre (5⁄128 in) long, the first birth is milky white, then become yellow-brown, there will be a black spot before hatching. Larvae have 5 instars generally, the larva body length of mature stage is about 15–18 millimetres (19⁄32–23⁄32 in). They have a brown head, the thorax and abdomen are green at first, then become yellowish-green, and reddish brown when they are mature. There are 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. Pupae are about 9 millimetres (23⁄64 in) 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.