Development and optimization of the Suna trap as a tool for mosquito monitoring and control

Abstract

Background: Monitoring of malaria vector populations provides information about disease transmission risk, as well as measures of the effectiveness of vector control. The Suna trap is introduced and evaluated with regard to its potential as a new, standardized, odour-baited tool for mosquito monitoring and control.

Methods: Dual-choice experiments with female Anopheles gambiae sensu lato in a laboratory room and semi-field enclosure, were used to compare catch rates of odour-baited Suna traps and MM-X traps. The relative performance of the Suna trap, CDC light trap and MM-X trap as monitoring tools was assessed inside a human-occupied experimental hut in a semi-field enclosure. Use of the Suna trap as a tool to prevent mosquito house entry was also evaluated in the semi-field enclosure. The optimal hanging height of Suna traps was determined by placing traps at heights ranging from 15 to 105 cm above ground outside houses in western Kenya.

Results: In the laboratory the mean proportion of An. gambiae s.l. caught in the Suna trap was 3.2 times greater than the MM-X trap (P < 0.001), but the traps performed equally in semi-field conditions (P = 0.615). As a monitoring tool , the Suna trap outperformed an unlit CDC light trap (P < 0.001), but trap performance was equal when the CDC light trap was illuminated (P = 0.127). Suspending a Suna trap outside an experimental hut reduced entry rates by 32.8% (P < 0.001). Under field conditions, suspending the trap at 30 cm above ground resulted in the greatest catch sizes (mean 25.8 An. gambiae s.l. per trap night).

Conclusions: The performance of the Suna trap equals that of the CDC light trap and MM-X trap when used to sample An. gambiae inside a human-occupied house under semi-field conditions. The trap is effective in sampling mosquitoes outside houses in the field, and the use of a synthetic blend of attractants negates the requirement of a human bait. Hanging a Suna trap outside a house can reduce An. gambiae house entry and its use as a novel tool for reducing malaria transmission risk will be evaluated in peri-domestic settings in sub-Saharan Africa.

Figure 1

Cross-sectional schematic view of the Suna trap. When connected to a power supply the ventilator rotates and generates airflow under the cover of the trap. The air moves around an odour-bait (here shown as brown strips of nylon), which is suspended inside the trap between the catch bag and plastic trap cover. The air becomes saturated with odour that is attractive to mosquitoes. Air plumes leave the trap through holes in the trap base (blue arrow) and mosquitoes fly towards this attractive cloud of odour, as well as a plume of CO₂, which is released through a pipe in the trap base. Mosquitoes that come close to the trap are sucked into the trap through the funnel and ventilator (grey arrow) and are captured in a bag where they die due to dehydration.

Figure 2

Mean proportion of females caught in each trap type in A: laboratory conditions (n = 50 females released per replicate), B: semi-field conditions (n = 200 females per replicate). Error bars indicate ± 2 SEM. ***indicates P < 0.001 for a difference in the distribution of mosquitoes between the two traps.

Figure 3

Mean nightly catch sizes in the A: CDC LT (light off), MM-X trap and Suna trap, B: CDC LT (light on), MM-X trap and Suna trap during experiments in the MalariaSphere. (Error bars represent ± 2 SEM, N = 8 trap nights for each trap during each series of experiments, n = 200 female An. gambiae released during each experimental night). ***indicates P < 0.001 for a difference in catch size, relative to the CDC LT.

Figure 4

Mean female An. gambiae s.s. house entry per night (N = 16 nights control, 16 intervention, n = 200 females released each night). *** indicates P < 0.001 for a difference between means using a GLM with Poisson distribution and log link function. Error bars indicate ± 2 SEM.

Figure 5

Estimated marginal mean catch sizes for female mosquitoes caught in Suna traps at varying heights above ground, and in an MM-X trap positioned at 15 cm above the ground, outside houses in the field. Means are adjusted for day of sampling (An. gambiae s.l. only) and house (all species). Error bars represent ± 2 SEM. Different letters above bars indicate significant differences in catch sizes (A and B for An. gambiae s.l., C and D for An. funestus, E and F for Culex spp).