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

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Abstract
We evaluated the impact of sweetpotato weevil ( Cylas formicarius (Fabricius); Coleoptera: Apionidae) and of other direct pests and diseases (rats, Ceratocystis fimbriata, white grubs, rootrots and root cracks), and the effectiveness of C. formicarius sex pheromone traps at the farm level in four villages in East and Central Java, Indonesia during 1994 - 1996. Marketable yields of sweetpotato and damage from weevils and from other pests and diseases 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 yield from 3.32 to 2.50 kg/m2. During the wet season damage from sweetpotato weevil and from other pests and diseases dropped to 2.1 and 12.7% respectively. Varietal differences in damage from weevil and from other pests and diseases were not significant. In field trials with sex pheromone, lure loadings of 10, 50 and 100 mug placed at trap densities of 9, 25 and 100 traps/ha the average yield was 2.41 kg/m2 with sweetpotato weevil and other direct pests and diseases accounting for losses of 2.7% and 4.7% respectively. However, there were significant location-specific differences in weekly trap catch averages and in seasonal trap catch patterns. Trap catches ranged from averages of 475 and 584 weevils/week in the villages of Bendunganjati and Turi to 254 and 46 weevils/week in Ngargoyoso and Kradenan. The highest trap catches occurred at the highest sex pheromone loadings in all four locations. The effect of trap density on average weekly trap catch depended on location, with no significant effect of trap density on trap catch when the data from all locations were pooled. There was no statistically significant impact of sex pheromone traps on losses from sweetpotato weevil, although fields with blank lures had consistently higher levels of sweetpotato weevil damage. The highest trap catches occurred in Turi, which also had the highest levels of weevil damage. The use of sex pheromone traps led to damage reduction, even when weevil pressure and damage levels were low, as in 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 pressure.

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