Specificity of Response to Sex Pheromones Among Sweetpotato Weevils, Cylas puncticollis and C. brunneus

Abstract

Trapping experiments were carried out in Uganda and Indonesia with decyl (E)-2-butenoate and dodecyl (E)-2-butenoate, previously identified as components of the female sex pheromones of the African species of sweetpotato weevil, Cylas puncticollis and C. brunneus, respectively. In Uganda, decyl (E)-2-butenoate attracted only C. puncticollis males, but dodecyl (E)-2-butenoate attracted males of both C. brunneus and C. puncticollis. Catches of C. puncticollis with both compounds were higher when they were dispensed from polyethylene vials rather than rubber septa, while dodecyl (E)-2-butenoate dispensed from rubber septa gave higher catches of C. brunneus and was more selective for this species. Release rates of the two compounds from the two types of dispenser were measured in the laboratory and possible explanations for differences in dispenser performance considered. Lures containing decyl (E)-2-butenoate were as attactive to male C. puncticollis as 10 live virgin female C. puncticollis weevils, but lures containing dodecyl (E)-2-butenoate were not always as attractive to male C. brunneus as the conspecific virgin female weevils. Dose–response relationships with the synthetic pheromones varied between repeat experiments and with the type of dispenser. Addition of dodecyl (E)-2-butenoate to decyl (E)-2-butenoate either did not affect or increased catches of C. puncticollis males, but adding 1% or more of decyl (E)-2-butenoate to dodecyl (E)-2-butenoate significantly reduced attractiveness to C. brunneus. Traps baited with synthetic lures captured male C. brunneus weevils mostly early in the evening while the majority of male C. puncticollis were trapped between 01:00 hr and 03:00 hr. This clear temporal separation of activity of males of the two species helps to ensure species specificity of mating in these sympatric species. In Indonesia, dodecyl (E)-2-butenoate but not decyl (E)-2-butenoate attracted C. formicarius males, but this attractiveness was less than 0.4% that of the pheromone of C. formicarius, (Z)-3-dodecenyl (E)-2-butenoate.