SEASON-LONG CONTROL OF YELLOW STEM BORER, SCIRPOPHAGA-INCERTULAS (LEPIDOPTERA, PYRALIDAE) BY MATING DISRUPTION WITH THE NATURAL RATIO OF PHEROMONE COMPONENTS

Control of yellow stem borer, Scirpophaga incertulas (Walker), in rice was attempted by mating disruption using the natural ratio of pheromo ne components, a 1:3 blend of (Z)-9- and (Z)-11-hexadecenal, in replic ated trials at three locations in Andhra Pradesh, India, during the 19 94 and 1995 dry seasons. The pheromone was formulated in Selibate(R) a nd applied by hand at a rate of 40 g a.i./ha. In Medchal and Nellore, pheromone-mediated communication was reduced by at least 94% for the f irst 50 and 64 days after application respectively, as measured by phe romone trap catch suppression. Compared with adjacent farmers' practic e plots, subsequent dead heart and white head damage were reduced by 7 4 and 63% and 83 and 40% in Medchal and Nellore, respectively. In Medc hal, average rice yields were increased compared to the farmers' pract ice plots, 4108 and 3835 kg/ha respectively, but in Nellore, they were the same as those obtained in the farmers practice plots, 6400 and 67 33 kg/ha respectively. In Warangal, the level of communication disrupt ion over the first 70 nights after pheromone application was less than obtained in either Medchal or Nellore and averaged between 50 and 87% . The maximum dead heart and white head damage recorded in the pheromo ne-treated plots in Warangal were 2.8 and 15.7% respectively compared to 7.0 and 20.9% respectively in the farmers' practice plots. Differen ces in S. incertulas larval damage estimates obtained from the pheromo ne-treated and farmers' practice plots in Warangal were reflected in g rain yields, 4036 and 3715 kg/ha respectively. Surveys of insecticide use indicated that 92% of smallholders in Medchal applied insecticide at least once per season while in Warangal over 60% applied insecticid e on two or more occasions. The data show that season-long control of S. incertulas comparable to that obtained with conventional insecticid es can be achieved by mating disruption in smallholder rice fields in India.