Abstract:
Cosmopolites sordidus is a major pest of plantain in most plantain growing regions in the world and causing 34.8% yield loss in Ghana. Infochemicals (pheromones and kairomones) can be a potential monitoring tool for plantain weevil borer Cosmopolites sordidus Germar (Coleoptera: Curculionidae). The adult weevil produces an aggregation pheromone which attracts both males and females and the attractive compound Sordidin has been identified and synthesised for commercial purpose. The objective of this research was to evaluate the effectiveness of the pheromone for monitoring the plantain weevil under Ghanaian conditions and to find suitable plantain cultivars that can serve as trap crops for the C. sordidus. Trap effectiveness was conducted in the field in three seasons (major rainy season, minor rainy season and dry season) from June 2012 to February 2013 and traps were examined twice a week and adults sexed into males and females. In all the seasons, pheromone traps attracted a total of 739 (68.36%) adults, corm traps attracted 196 (18.13%) adults, pseudostem traps attracted 146 (13.51%) adults and the pitfall (control) traps recorded no weevil (0%). More female than male C. sordidus were captured in all three trials in a ratio of 2:1. In this study pheromone traps attracted the highest number of females followed by corm traps and pseudostem traps and differences between them were statistically significant at P=0.05. C. sordidus abundance was negatively related to rainfall (R2= 0.69) and temperature (R2= 0.58), the number of C. sordidus trapped was highest during the driest months of the study (August, December and February). In the evaluation of trap sizes, the study showed that the 4L pitfall traps were the most effective trap sizes for pheromone trapping of the C. sordidus. The 4L pitfall traps significantly captured the highest percentage of weevils (50.3%), followed by the 8L pitfall traps (29.2%) and 12L pitfall traps (20.5%), indicating that trap performance can be maximized with the use of 4L pitfall traps. The varietal preference test
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using Brodewuio, Apantu pa and Apem to C. sordidus in a choice assay showed that Brodewuio (37.2%) and Apantu pa (36.5%) attracted significantly more weevils compared with Apem which attracted (26.35%) weevils and Yam (control) attracted no weevils. Based on this result, Brodewuio was considered the most preferred cultivar than Apantu pa and Apem. Pheromone lures of the plantain weevil could offer an effective means of monitoring and managing the population of the plantain weevil in Ghana because it was 4 and 5 times more effective than corm and pseudostem traps respectively.
