Stem borers are considered important insect pests of rice in most parts of the world. They have been implicated as the major constraint to rice production in West Africa (Ukwungwu 1990). Reliable data on yield loss caused by stem borers are not available in southeastern Nigeria. However, a screenhouse experiment at Badeggi, in the middle belt of Nigeria, showed that yield loss caused by Diopsis thoracica (West) ranged from 5% to 19% (Akinsola 1980). Dakuo et al (1991) reported a yield loss of 33% in irrigated rice caused by lepidopterous stem borers (Chilo zacconius, C. diffusilineus, Maliarpha separatella, and Sesamia calamistis) in Burkina Faso.
Various control strategies have been adopted against stem borers, one common method being the use of synthetic insecticides, which can be environmentally disruptive and can result in the accumulation of residues in the harvested produce (Chinniah et al 1998). The use of synthetic insecticides is rare in southeastern Nigeria, where farmers produce the bulk of the rice. Although some risks accompany the use of synthetic insecticides, some insecticides of plant origin are safer to handle and use. Neem products are examples of such plant-derived insecticides, which have been used in some Asian countries. Their use on field crops is not yet popular in Nigeria. Our study reports the effect of the frequency of application of 5% neem seed kernel extract (NSKE) on rice stem borer damage and grain yield.