Activity Rhythm of the Banana Weevil, Cosmopolites sordidus Germar (Coleoptera: Curculionidae)

Laboratory and field investigations in Kenya, East Africa, on the activity rhythm of the banana weevil, Cosmopolites sordidus Germar indicated a nocturnal lifestyle for this pest. This behavior persisted even under constant dark (DD) condition during free-running trials. This proved an endogenously controlled, true circadian rhythm for the pest. Activity generally commenced sharply with the start of scotophase (6 pm) reaching peak at about 9pm and maintaining that level till about 4am, and gradually declined with the start of photophase (6am). Light was a major deterrent to the pest, as constant light (LL) condition completely suppressed activity. Temperature and light intensity correlated negatively with weevil activity (r=-0.726, P<0.01; r=-0.690, P<0.01 respectively), but correlated positively with relative humidity (r=0.821, P<0.001). These findings provide baseline information on the behavior of the pest, and will help to guide timing of future laboratory and field experiments on the pest.