Population Dynamics of the Plantain-Banana Weevil, Cosmopolites sordidus Germar (Coleoptera: Curculionidae) in Bayelsa State, Southern Nigeria

Population dynamics studies reveal the fluctuations in an organism’s population over time, in relation to prevailing climatic conditions; thus providing a fundamental background for evaluating and determining appropriate control strategies for adoption. This study in Bayelsa State, Southern Nigeria has revealed that C. sordidus population experiences a gradual build-up with onset of rains (early March), and attain peaks between May and early November. The population however, declines with the commencement of the dry season in November, and continues till February (just before the wet season). Rainfall frequency was found to be the main factor influencing the pest’s population (i.e. not merely monthly precipitation or Total rainfall); the correlations were positive and significant at both Okarki and Akenfa (r=0.540, P<0.05; r= 0.515, P<0.05) respectively. Average Relative humidity similarly had a significant correlation with the pest’s population at Okarki and Akenfa (r=0.516, P<0.05; r=0.565, P<0.05). Consequently the dry season (November – February) often associated with both low rainfall and rainfall frequencies, and with low relative humidity, witnessed significant falls in the pest’s population. Temperature did not show any significant influence on the pest’s population performance at all the locations in this study, obviously because survey/sampling times were restricted to daytimes only. This pest is known to have a nocturnal rhythm. It is recommended that controls against this pest be targeted between November and February, as it appears the most appropriate period to prevent the pest’s population from rising and reaching alarming and destructive levels.