Laboratory studies on behavioural interactions of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) with conspecifics, synthetic pheromone and the predator Teretriosoma nigrescens (Lewes) (Coleoptera: Histeridae)

A bioassay method was devised to test the responses of adult Prostephanus truncatus (Horn) to conspecific adults or synthetic pheromone and to observe the response of the predator Teretriosoma nigrescens (Lewes) to adult or larval P. truncatus or the synthetic pheromone of this species. The results confirmed earlier observations that male P. truncatus are the source of a pheromone attractive to both males and females, P. truncatus adults (in this case virgin females) are disinclined to leave food in response to the pheromone and maize itself is relatively unattractive to P. truncatus. For the first time it has been demonstrated that males are not attracted to females, females repel or avoid each other and males are less attracted to the naturally produced pheromone secretion than are females. In view of the fact that unmated females will not leave food to locate a calling male it was concluded that the female response to the pheromone is primarily a means of locating a food source, rather than a sexual partner. In contrast, males release their secretion to attract females. When adult P. truncatus were tested against grains treated with the synthetic pheromone the response of males and females was apparently identical, in contrast to the lower response of males when tested against conspecific males. It seems probable that the amounts of pheromone used when testing the synthetic mixture are greater than would be produced naturally by a calling male and that this may mask the apparently lower sensitivity of males to the natural pheromone. The pheromone of P. truncatus is known to be a kairomone for T. nigrescens, but in the bioassay this species was not attracted to synthetic pheromone and responded more strongly to empty maize grains than to adult or larval P. truncatus. It would appear that when walking, adult T. nigrescens are unwilling to approach closely to P. truncatus. The possible significance of this is discussed.