Newly hatched larvae enter leaf sheaths and begin feeding on the inner tissues. Damaged leaf sheaths that have been attacked have transparent patches that later turn yellowish-brown and eventually become dry.
After a few days, the larvae leave the sheaths and bore into the stem.
Larvae feed on the tissues around the node. As a result, the infested stems are weakened and easily break. Occasionally, stem borers eat through the node and bore down the stem. Others leave the stem above the node and enter either another tiller or a neighboring internode of the same stem.
As they grow, the larvae of rice stem borer molt (cast off their old exoskeleton) five times before pupating. The full-grown larvae, before pupating, cut exit holes in the internodes through which the emerging moths later escape. Usually the opening of these exit holes are plugged with fine white web and cannot be easily detected before the moths have escaped.
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