Territorial aggression among males of three syrphid species

Among territorial syrphids, Eumerus tuberculatus (Rond.) males are always less aggressive than Merodon equestris (Fab.) and Eristalis tenax (L.) males. This aggressive gradient is maintained despite the fact that the aggressive intensity of all three species increases with the density of conspecifies, varies with insect age and stage, and ceases if temperatures fall below a certain critical level or if sunlight disappears. Possible reasons for the difference in the inherent level of aggression are discussed. Males of all three species recognized conspecifie females through a combination of visual and behavioural cues. A territorial male approached all other intruders aggressively but attempted to mate with them if, like females, the intruders did not respond to the male's approach. Differences in behaviour patterns among species are tentatively traced to different energy budgets and mating strategies. Within each species, males and females show different temperature thresholds for activity. This finding is discussed in terms of energy requirements and reserves. The final two sections of the thesis deal with the agricultural implications of these results and with possibilities for future studies.Land and Food Systems, Faculty ofGraduat