Behavioural Ecology and Spatial Dynamics of Anopheles coluzzii Swarms

Swarming is a feature of the mating system of malaria mosquitoes, yet the mechanisms shaping its dynamics and the contribution of females remain largely overlooked. In this thesis, I investigate the behavioral ecology and spatial dynamics of Anopheles coluzzii swarms using a combination of laboratory and semi-field recordings with three-dimensional tracking and descriptive modeling.

Contrary to the long-held view of swarming as a male-dominated process, I show that females also engage in sustained and structured swarming behavior. Using infrared stereoscopic videography, I found that females maintain swarming activity well beyond sunset, and fly at higher speeds. Mating status emerged as a key determinant, as virgin females spent significantly longer above swarm markers compared to mated ones, whose behavior likely shifted towards host-seeking. By integrating these laboratory results with field mating rates, I developed a behavioral model predicting that, although virgins make up only a small proportion of the field population, they are overrepresented in swarms due to prolonged residence times, but their presence declines rapidly as mating proceeds.

Semi-field recordings further revealed that sex ratio strongly influences swarm cohesion and stability. Male-biased swarms formed dense and stable aggregations, whereas more balanced or female-biased groups remained diffuse and form looser aggregates. These results emphasize that operational sex ratio is a unique ecological factor shaping swarm structure and mating opportunities.

Finally, through a systematic review across insect taxa, I contextualize female swarming within a broader evolutionary framework. Evidence from other diptera suggests that female aggregation may serve roles beyond mating, including predator avoidance and spatial orientation. I therefore propose that female swarming in An. coluzzii is a conditional, facultative behavior expressed under specific ecological and physiological circumstances rather than an invariant trait.

Taken together, this work defines and reproposes (female) mosquito swarming as a sexually interactive process shaped by sex, mating status, and its ecological context. By characterizing the spatial dynamics of swarm formation and highlighting female participation, it provides new insights into the reproductive ecology of malaria vectors. In addition, the methodological pipeline developed here are fully open-source tools which offers a foundation for future studies. Beyond its fundamental contribution to behavioral ecology, this thesis identifies swarming as a promising target for novel, behaviorally informed vector control strategies.