Characterization of the swarming behavior of Anopheles coluzziiand Anopheles gambiae(Diptera: Culicidae) populations in a hybrid zone of Senegal

Anopheles gambiaeand Anopheles coluzzii, often found in sympatry and synchronous, have undergone a premating reproductive isolation across their distribution range. However, in the Western coast of Africa, unexpected hybridization zones have been observed, and little is known about swarming behavior of these cryptic taxa. Here, we characterized the swarming behavior of An. coluzziiand An. gambiaeto investigate its role in the high hybridization level in Senegal. The study was conducted in the south and central Senegal during the 2018 rainy season. Mating swarms of malaria vectors were surveyed at sunset and collected using an insect net. Meanwhile, indoor resting populations of malaria vectors were collected by pyrethrum spray catches. Upon collection, specimens were identified morphologically, and then members of the An. gambiaecomplex were identified at the species level by polymerase chain reaction (PCR). An. gambiaeswarmed mainly over bare ground, whereas An. coluzziiwere found swarming above various objects creating a dark–light contrast with the bare ground. The swarms height varied from 0.5 to 2.5 m. Swarming starting time was correlated with sunset whatever the months for both species, and generally lasted about 10 min. No mixed swarm of An. gambiaeand An. coluzziiwas found even in the high hybridization area. These results indicated a premating isolation between An. coluzziiand An. gambiae.However, the high hybridization rate in the sympatric area suggests that heterogamous mating is occurring, thus stressing the need for further extensive studies.