General Information

Common name: Rice caseworm
Scientific name: Nymphula depunctalis
Lepidoptera:Pyralidae

Host plants

Rice

Distribution

Argentina, Australia, Brazil, China, India, Japan, Malagasy Republic, Malawi, Malaysia, Mauritius, Mozambique, Nigeria, Pakistan, Philippines, Republic of Congo, Sri Lanka, Thailand, Uruguay, and Venezuela

Damage

The feeding damage is the removal of leaf tissue which leaves a ladder-like appearance. This is caused by the back and forth motion of the larva's head while feeding. It feeds by scraping the green tissues of young leaves in patches, leaving behind the white epidermis. The damage is not uniform because the larvae floating in their cases are easily carried in any direction by wind or by water current. Usually, the damaged plants can recover when no other defoliating pests are present.

Description

Eggs are circular, and flattened and have smooth surfaces. They are light-yellow and turn darker as these mature. The eggs are laid in one or two adjacent rows on the lower surface of the leaves or on the leaf sheath near the water surface. As an egg develops, 2 purplish-dots are visisble which are the eyes of a developing larva. The egg development is 2-6 days.

The newly hatched larva is pale-cream and turns greenish from the second instar onward. It has a light-yellow head. The larva feeds immediately after hatching. Two days later, it encloses itself within a tubular leaf case, by cutting the leaf blade on one side of the midrib with the two margins bound together into a tubular structure by a silken thread, which it secretes. Each time the larva molts, it makes a new case. It attaches its case to the rice plant to feed on the leaves. Before pupation, the larva closes the upper and lower ends of the case while attached to the rice stem slightly above the water level. The larval stage has five instars which takes about 20 days.

The pupa is about 5.5 mm long and 1.5 mm wide. It has a creamy color. It turns silvery-white as it matures. Pupation takes about a week.

The adult moth is bright-white with light-brown and black spots. It is about 5 mm long with a wing expanse of about 15 mm. The adults are nocturnal and live from 4 to 8 days. The females live longer that the males. A female is capable of oviposition after two days and she can lay as many as 50 egg masses, with each eggmass of 10-20 eggs.