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

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 puncticollisand C. brunneus, respectively. In Uganda, decyl (E)-2-butenoate attracted only C. puncticollismales, but dodecyl (E)-2-butenoate attracted males of both C. brunneusand C. puncticollis.Catches of C. puncticolliswith 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. brunneusand 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. puncticollisas 10 live virgin female C. puncticollisweevils, but lures containing dodecyl (E)-2-butenoate were not always as attractive to male C. brunneusas 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. puncticollismales, 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. brunneusweevils mostly early in the evening while the majority of male C. puncticolliswere 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. formicariusmales, but this attractiveness was less than 0.4% that of the pheromone of C. formicarius, (Z)-3-dodecenyl (E)-2-butenoate.