Sex pheromones of Callosobruchus subinnotatus and C-maculatus (Coleoptera : Bruchidae): congeneric responses and role of air movement

Females of Callosobruchus spp. are known to produce sex pheromones that att ract males. These sex pheromones cannot be adopted for use in pest manageme nt without first investigating the responses of the males in the windless c onditions of storage environments. Consequently, behavioural bioassays of C allosobruchus subinnotatus Pic males were conducted in an olfactometer in t he absence of air-flow. Under these conditions males were found to be able to follow odour trails to the source. However, the latency period was longe r in diffusional bioassays than for insects in a Y-tube olfactometer that p rovided directional wind cues. The highest percentage of males reached the pheromone source when components of the pheromones, (E)-3-methyl-2-heptenoi c acid (E32A) and (Z)-3-methyl-2-heptenoic acid (Z32A), were formulated in a 50:50 or 25:75 ratio. Males of C. maculatus (Fabricius) responded to sex pheromone of C. subinnotatus, but males of C. subinnotatus did not respond to that of C. maculatus. The two sex pheromone components of C. subinnotatu s are also constituents of C. maculatus sex pheromone. These two components may be potentially useful in monitoring the populations of both species in stored beans. It is postulated that (Z)-3-methyl-3-heptenoic acid (Z33A), the major component of the sex pheromone of C. maculatus, must have acted a s an antagonist inhibiting response of C. subinnotatus to the sex pheromone of C. maculatus.