Semi-field and indoor setups to study malaria mosquito swarming behavior

Abstract

Background The recent resurgence of interest in sterile insect techniques to control vector mosquitoes has renewed interest in novel methods for observing mating behavior. Malarial vectors of the Anopheles gambiae complex are known to mate in swarms at specific locations at dawn and dusk. Most knowledge of mosquito swarming behavior is derived from field observations and a few experimental studies designed to assess critical parameters that affect mosquito swarming. However, such studies are difficult to implement in the field because of uncontrollable environmental factors and mosquito conditions. Here, we present two experimental setups specifically designed to analyze mosquito swarming behavior and provide evidence that swarming behavior of mosquitoes can be generated and accurately assessed under both semi-field and laboratory conditions. Methods The Mosquito Ecology Research Facility setup is a semi-field enclosure made of 12 compartments (10.0 × 6.0 × 4.5 m L × W × H each) exposed to ambient meteorological and lighting conditions. The laboratory setup consists of a windowless room (5.1 × 4.7 × 3.0 m) in which both environmental and mosquito conditions can be controlled. In the two setups, 300 3–6-days-old An. coluzzii virgin males were released and some swarm characteristics were recorded such as the time at which the swarm started, the number of mosquitoes in the swarm and the height. Climatic conditions in the semi-field setup were also recorded. Results In both setups, An. coluzzii males displayed stereotyped and consistent swarming behavior day after day; males gradually gather into a swarm over a ground marker at sunset, flying in loops in relation to specific visual features on the ground. Although semi-field climatic conditions were slightly different from outdoors conditions, they did not impede swarming behavior and swarm characteristics were similar to those observed in the field. Conclusions Swarm characteristics and their consistency across days provide evidences that these facilities can be used confidently to study swarming behavior. These facilities come to complement existing semi-field setups and pave the way for new experimental studies which will enhance our understanding of mating behavior but also mosquito ecology and evolution, a prerequisite for application of genetic approaches to malaria control.

Sex aggregation and species segregation cues in swarming mosquitoes: role of ground visual markers

“…The laboratory and semi-field experiments were performed in setups described by Niang et al [49]. Briefly, the laboratory setup (swarming room) is a room without windows measuring 5.10 m in length, 4.70 m wide and 3 m high and equipped with a set of stimuli designed to induce swarming behavior.…”

“…Among these stimuli: (i) the ambient light is dimmed from full light to full dark in a 30 min time set to simulate sunset and to initiate the swarming behavior; (ii) a bright horizon on one wall allows the swarming behavior to last and to observe mosquitoes. The semi-field setup is made of 12 compartments (10 × 6 × 4.5 m each; L × W × H) with walls made of polyester net with 346 holes/inch 2 allowing airflow and natural light diffusion (for details see [49]).…”

No Evidence for Long-range Male Sex Pheromones in Two Malaria Mosquitoes

“…For the same purpose, we provided an artificial twilight horizon made of a 40 W incandescent bulb (2,500 K) located on the floor between a white wall and a 50 cm high black horizon [34,61,62]. Inside, females of the two species were released in equal numbers into the releasing cage of the olfactometer allowing them to acclimate for 30 min before sunset.…”

“…Because compounds can be emitted at a given time and only produced in tiny quantities by a single male, we chose to work directly on swarms. Three different sampling methods were used in Burkina Faso; two methods were run in a laboratory setup [62] and one in the field. Carbotrap® (60-80 and 20-40 mesh, respectively; Sigma Aldrich, Munich, Germany)(See [63]).…”

“…Flow rates and extraction durations were dependent on the odor trap (See Table 1). The entire setup was placed in a room specially designed to stimulate Anopheles male swarming behavior thanks to a set of visual stimuli (lights and ground marker, see [62] for details).…”