Farmer-managed trials in south-east Nigeria to evaluate the rice variety Cisadane and estimate yield losses caused by the African rice gall midge, Orseolia oryzivora Harris & Gagne

Farmer-managed trials of the rice variety Cisadane were undertaken at 47 ra infed lowland sites around Abakaliki, south-east Nigeria, a major outbreak area of the African rice gall midge (ARGM). At each site a plot of Cisadane was grown alongside a control plot of the participating farmer's usual var iety. On average the Cisadane yielded 26% higher than the controls but ARGM infestation levels on it were only slightly lower, suggesting that it had greater tolerance to the pest but little antixenotic or antibiotic resistan ce. For all of 14 evaluation criteria, most participating farmers rated Cis adane as better than their control varieties. It appears to be a useful com ponent for an ARGM management strategy. Regression analyses of yield on alt ernative variables for ARGM infestation derived from data recorded at 3, 7 or II w.a.t. (weeks after transplanting) showed that the log-transformed pe rcent tiller infestation at 7 w.a.t. was the best predictor of yield. Varia bles for site topography, water level, fertilizer use in the nursery, and p lant spacing also had significant partial regression coefficients. Excludin g plots with tiller infestation levels above 30%, the relationship between yield and infestation was approximately linear and suggested a yield loss o f 2.9% per 1% increase in infestation.