The copulation behaviour of the western flower thrips

The western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a major pest of agricultural and horticultural importance in most parts of the world. It damages crops by feeding and transmission of viruses. There is a need for sustainable IPM due to development of resistance to insecticides. Understanding the reproductive biology of this pest may suggest novel approaches to pest control. The aim of this research was to study the copulation behaviour of F. occidentalis and the possible role of pheromones. Female F. occidentalis copulated multiple times with virgin males either in rapid succession or over days, contrary to previous reports that females will not copulate again until after fifteen days. Subsequent copulations were, however, shorter than the first, probably due to detection of a barrier by males that may prevent sperm transfer. Culture reared males copulated with virgin females, but rarely with copulated females, and virgin males copulated with dead virgin females more often than with dead mated females of similar age, which showed that males could detect whether females had copulated. Observation suggested that during copulation, males were applying antiaphrodisiac pheromone by stroking or antennation, which may have been used for assessing females’ copulation status. This antiaphrodisiac pheromone may be the contact pheromone, 7-methyltricosane. Culture reared males were probably limited in reproductive resources due to old age or multiple copulation, thus they could have changed strategy to show preference for virgin females, copulating more with them than already copulated females, whereas, most young virgin males (with more resources) were not mate selective. It is also possible that the increased preference for virgin females resulted from male mating experience. Choice based on male copulation status was not observed in virgin females