Background Malaria mosquitoes reproduce in mating swarms. Previous studies have reported a pronounced activity peak in male mosquito swarms immediately following simulated sunset, typically lasting around 20 min. This peak represents the main swarm formation, where several mosquitoes concentrate above visual markers and maintain prolonged flight activity. However, most studies rely on laboratory setups with balanced or single-sex swarms, which do not reflect the male-biased sex ratios observed in the field. Methods In this study, we studied swarming behavior of male and female Anopheles coluzzii mosquitoes in five sex ratios (male-only 1:0, male-biased 3:1, balanced 1:1, female-biased 1:3, female-only 0:1) using three-dimensional infrared videography to quantify spatial structure of swarms and flight speed of individual mosquitoes. For each ratio, we analyzed changes in spatial arrangement and flight speed through time and between conditions. Results Swarm volume varied following a quadratic trend (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">${R}^{2}=0.889$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi>R</mi> </mrow> <mn>2</mn> </msup> <mo>=</mo> <mn>0.889</mn> </mrow> </math></EquationSource> </InlineEquation>). As the proportion of females in the swarm increased, the volume of the swarm increased, ranging from 305.1 cm3 in male-biased swarms to 612.6 cm3 in female-only swarms. Mean flight speed also increased with female proportion, from <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$0.66$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>0.66</mn> </mrow> </math></EquationSource> </InlineEquation> m/s (1:1 balanced ratio) to <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$0.87$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>0.87</mn> </mrow> </math></EquationSource> </InlineEquation> m/s (0:1 female-only ratio), showing a moderate relationship with volume (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">${R}^{2}=0.504$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi>R</mi> </mrow> <mn>2</mn> </msup> <mo>=</mo> <mn>0.504</mn> </mrow> </math></EquationSource> </InlineEquation>). Swarm density and speed were negatively correlated, indicating that mixed swarms are not only smaller in volume but also exhibit higher track densities (<InlineEquation ID="IEq5"> <EquationSource Format="TEX">${R}_{ \text{Spline}}^{2}=0.712)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>R</mi> <mrow> <mtext>Spline</mtext> </mrow> <mn>2</mn> </msubsup> <mrow> <mo>=</mo> <mn>0.712</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> suggesting tighter, slower swarms in male-rich groups. Furthermore, we used a Random Forest as an exploratory classifier to (1) identify which kinematic features most differentiate operational sex ratio (OSR) groups and (2) test, as a proof of concept, whether sex ratio can be inferred from kinematic signatures. Conclusions These results demonstrate the influence of sex ratio on swarm kinematics and support the use of machine learning for behavioral classification in mosquito ecology. Graphical abstract

Sex ratios influence spatial occupancy and kinematic stability of Anopheles coluzzii mosquito swarms

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2026年1月28日

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Sofia Vielma,
Simon P. Sawadogo,
Tarwendpanga F. X. Ouédraogo,
Antoine Cribellier,
Florian T. Muijres,
Abdoulaye Diabate,
Ruth Müller

摘要

Background

Malaria mosquitoes reproduce in mating swarms. Previous studies have reported a pronounced activity peak in male mosquito swarms immediately following simulated sunset, typically lasting around 20 min. This peak represents the main swarm formation, where several mosquitoes concentrate above visual markers and maintain prolonged flight activity. However, most studies rely on laboratory setups with balanced or single-sex swarms, which do not reflect the male-biased sex ratios observed in the field.

Methods

In this study, we studied swarming behavior of male and female Anopheles coluzzii mosquitoes in five sex ratios (male-only 1:0, male-biased 3:1, balanced 1:1, female-biased 1:3, female-only 0:1) using three-dimensional infrared videography to quantify spatial structure of swarms and flight speed of individual mosquitoes. For each ratio, we analyzed changes in spatial arrangement and flight speed through time and between conditions.

Results

Swarm volume varied following a quadratic trend ( ${R}^{2}=0.889$ $R^{2} = 0.889$ ). As the proportion of females in the swarm increased, the volume of the swarm increased, ranging from 305.1 cm³ in male-biased swarms to 612.6 cm³ in female-only swarms. Mean flight speed also increased with female proportion, from $0.66$ $0.66$ m/s (1:1 balanced ratio) to $0.87$ $0.87$ m/s (0:1 female-only ratio), showing a moderate relationship with volume ( ${R}^{2}=0.504$ $R^{2} = 0.504$ ). Swarm density and speed were negatively correlated, indicating that mixed swarms are not only smaller in volume but also exhibit higher track densities ( ${R}_{ \text{Spline}}^{2}=0.712)$ $R_{Spline}^{2} = 0.712)$ suggesting tighter, slower swarms in male-rich groups. Furthermore, we used a Random Forest as an exploratory classifier to (1) identify which kinematic features most differentiate operational sex ratio (OSR) groups and (2) test, as a proof of concept, whether sex ratio can be inferred from kinematic signatures.

Conclusions

These results demonstrate the influence of sex ratio on swarm kinematics and support the use of machine learning for behavioral classification in mosquito ecology.

Graphical abstract