Pheromonal Trapping of Chilo partellus(SWINHOE)(Lepidoptera:Pyralidae)Moths in Relation to Male Population Density and Competition with Females

The numbers of laboratory-reared males of Chilo partellus (SWINHOE) which were released, both in a screenhouse and in the field, and recaptured in virgin female-baited traps were positively correlated. Pheromone trap catches were reduced by 75-100% when 18 or 36 virgin females were placed in two concentric circles of radii 10 m and 20 m occupying an area of 1, 257 sq m. around the trap. Mated females surrounding the trap did not cause a significant decrease in the trap catch. Tethered virgin females surrounding a virgin female-baited trap competed successfully among themselves and with the trap for receptive males, the percentage of the tethered mated females being 58-66% and the catch in the trap reducing by 78-86% compared with that in the control. Thus, although catches of males in pheromone traps increased with the increase in their population density, the efficiency of the trap decreased due to competition with increasing number of calling females in the trap vicinity. The disruption in the catch was not accompanied by a corresponding reduction in mating. The results also demonstrated competition among pheromone traps.