Feeding damage at the base of the plant or along the central stem causes dead tillers at the vegetative stages ('deadhearts') and whitish unfilled panicles ('whiteheads') at the reproductive stages. After hatching, the larvae bore into the leaf sheath and feed on the inner surface of the stem. Tiny holes, frass and fecal matter can be observed on the damaged plant tissues. The larvae can move from one internode to another. During the vegetative stage, larval feeding may not cause visible symptoms because the plant compensates for the damage by producing extra tillers. But, this costs energy and ultimately yield will be affected.
The damage is caused by the larvae of the yellow stem borer, Scirpophaga incertulas, a pest of deepwater rice. It is found in plants or leaf-over stubbles in aquatic environments where there is continuous flooding. Young larvae wrap part of a leaf around their body and detach themselves from the plant, falling onto the water surface. They then attach themselves to the base of a new plant and bore into the stem. High nitrogenous field are highly favorable. Fields planted later in the season also favor the insect, whose population has built up in fields that have been planted earlier. As a comparison, the pest can cause about 20% yield loss in early planted rice, and 80% in late-planted crops.
Natural predators and parasitoids are numerous and include several species of ants, beetles, grasshoppers, flies, wasps, nematodes, mites, earwigs, birdsdragonflies, damselflies and spiders. Five to six releases of the egg parasitoid Trichogramma japonicum (100,000/ha) starting from 15 days after planting can be planned. Treatments include the application of products containing bacteria and fungi that affect the larvae (before it penetrate the stem). Neem extracts, bacillus thuringiensis can also be used for that purpose.
Always consider an integrated approach with preventive measures together with biological treatments if available. Preventive chemical treatment include the soaking of the roots of the seedlings in 0.02 chlorpyriphos for 12-14 hrs before transplanting (30 days protection). Apply the following insecticides based on fipronil, chlorpyrifos or chlorantraniliprole either as granules or spray once the threshold is reached (25-30 male moths/trap/week). Do not use broad-spectrum insecticides to fight pests.