CONTROL OF YELLOW STEM BORER, SCIRPOPHAGA-INCERTULAS (LEPIDOPTERA, PYRALIDAE) BY MATING DISRUPTION ON RICE IN INDIA - EFFECT OF UNNATURAL PHEROMONE BLENDS AND APPLICATION TIME ON EFFICACY

Single applications of slow-release pheromone formulations were used t o control yellow stem borer, Scirpophaga incertulas Walker, by mating disruption in two trials on rice in India. The first trial compared th e efficacy of two formulations containing 1:10:1 and 1:10:0 ratios of (Z)-9-hexadecenal, (Z)-11-hexadecenal and (Z)-9-octadecenal, component s of the S. incertulas pheromone, and a commercially-available formula tion, Selibate CS, containing the related Chile suppressalis Walker ph eromone, a 1:10:1 blend of (Z)-9-hexadecenal, (Z)-11-hexadecenal and ( Z)-13-octadecenal, with farmers' practice plots treated with insectici des. Pheromone trap catches indicated that in each of the pheromone-tr eated plots the catches of male moths were reduced by up to 98% compar ed with catches in the insecticide-treated plots suggesting that phero mone-mediated communication was disrupted. Larval damage ranged from 5 .7 to 8.1% white heads (WH) in the insecticide-treated plots compared to a significantly reduced range of 2.1 to 2.4% WH in the pheromone-tr eated plots. There was no significant difference between the damage es timates recorded for each of the different pheromone treatments. A sec ond trial compared the effect on efficacy of applying the two-componen t pheromone formulation on different dates, 9-12 and 39-44 days after transplanting. Both pheromone treatments gave significantly lower leve ls of WH damage compared to equivalent insecticide treated plots; 1.8, 2.0, and 6% respectively. In both trials rice grain yields increased by between 5 and 12% in pheromone-treated plots compared to insecticid e treated plots, which was due, at least in part, to the cumulative ef fect of reduced stem borer damage in both the tillering and reproducti ve stages of the crop cycle. The formulations exhibited pseudo-zero or der release rates with field lives of between 70 and 90 days.