Evaluation of the impact of sweetpotato weevil (Cylas formicarius) and of the effectiveness of Cylas sex pheromone traps at the farm level in Indonesia

We evaluated the impact of sweetpotato weevil (Cylas formicarius (Fabricius ); Coleoptera: Apionidae) and of other direct pests and diseases (rats, Cer atocystis fimbriata, white grubs, root rots and root cracks), and the effec tiveness of C. formicarius sex pheromone traps at the farm level in four vi llages in East and Central Java, Indonesia during 1994-1996. Marketable yie lds of sweetpotato and damage from weevils and from other pests and disease s were higher during the dry season, when damage from weevils reached 8.2% and the impact of other pests and diseases was 16.3%, reducing marketable y ield from 3.32 to 2.50 kg/m(2). During the wet season damage from sweetpota to weevil and from other pests and diseases dropped to 2.1 and 12.7% respec tively. Varietal differences in damage from weevil and from other pests and diseases were not significant. In field trials with sex pheromone, lure lo adings of 10, 50 and 100 mu g placed at trap densities of 9, 25 and 100 tra ps/ha the average yield was 2.41 kg/m(2) with sweetpotato weevil and other direct pests and diseases accounting for losses of 2.7% and 4.7% respective ly. However, there were significant location-specific differences in weekly trap catch averages and in seasonal trap catch patterns. Trap catches rang ed from averages of 475 and 584 weevils/week in the villages of Bendunganja ti and Turi to 254 and 46 weevils/week in Ngargoyoso and Kradenan. The high est trap catches occurred at the highest sex pheromone loadings in all four locations. The effect of trap density on average weekly trap catch depende d on location, with no significant effect of trap density on trap catch whe n the data from all locations were pooled. There was no statistically signi ficant impact of sex pheromone traps on losses from sweetpotato weevil, alt hough fields with blank lures had consistently higher levels of sweetpotato weevil damage. The highest trap catches occurred in Turi, which also had t he highest levels of weevil damage. The use of sex pheromone traps led to d amage reduction, even when weevil pressure and damage levels were low, as i n the village of Kradenan. This suggests that there is potential for traps to play a role in reducing weevil damage in situations of higher weevil pre ssure.