Mate choice in Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) : the role of male-produced aggregation pheromone

• Main Author: Birkinshaw, Lucy A.
• Published: University of Leicester 1998
• Subjects: 595.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.696433

Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) is a destructive pest of stored maize and cassava that has recently been accidentally introduced into tropical Africa. Males produce an aggregation pheromone when on food, that attracts dispersing males and females. P. truncatus aggregation pheromone is being used to monitor the spread of P. truncatus (Larger Grain Borer) across Africa. The biological function of this pheromone is controversial. This thesis investigates the role of aggregation pheromone in mate choice in P. truncatus. The literature on Coleopteran aggregation pheromones was reviewed, with particular reference to the possible adaptive functions of aggregation pheromones. Variation in Prostephanus truncatus aggregation-pheromone signalling was detected. Conspecifics can detect these differences and are preferentially attracted to some males more than others. Both males and females 'agree' which males are most attractive (shown in a laboratory bioassay and in trapping experiments in the field). Females also discriminate between potential mates on contact by a stylised pushing behaviour. Some males consistently secure more matings than others when two males are presented at once to a female. Discrimination between males mediated on contact through pushing is not influenced by the male's aggregation pheromone signal (both natural variation and manipulation of the pheromone signal were studied). Observation of adult beetles in an artificial host sandwiched between two glass plates revealed that males and females pair up, and cohabit within the same tunnel system. Pairs mate multiply (up to 20 times per 12 hours) and dissection of recently mated females revealed that males deliver an oversized ejaculate (approx. 50 000 sperm) as an oval spermatophore. Male investment in ejaculate was not found to be influenced by male crowding or the presence of Female Factor (an involatile pheromone produced by females, which can trigger aggregation pheromone shut down in males).