The "Gredouno" Cross Target: a new tool adapted to control Glossina palpalis gambiensis in the mangrove forests of Guinea

Abstract

Background: In the mangroves of Guinea, where the most active foci of human African trypanosomiasis in West Africa are located, vector control against tsetse flies using insecticide-impregnated Tiny Targets was first introduced in 2012. While annual deployments of Tiny Targets have resulted in an overall 90% reduction in tsetse fly densities in control areas, managing tsetse densities in specific biotopes such as mangrove channels, which are susceptible to significant climatic disturbances, presents greater challenges. Thus, a new three-dimensional model called the Cross Target was designed to address this situation.

Methods: In the first phase, we evaluated the attractiveness of the Cross Target along with three other devices (the Tiny Target, the biconical trap, and the pyramidal trap) in a Latin square design. In a second phase, we assessed the efficacy of the Tiny Target and the Cross Target to control tsetse densities in a pilot field study led in two adjacent mangrove channels.

Results: In the Latin square study, the Cross Target was significantly more attractive than the other devices, with a catch index of 2.23 (P = 0.03), 1.63 (P = 0.004), and 2.39 (P = 0.003) as compared with the biconical trap, the Tiny Target, and the pyramidal trap, respectively. In the pilot experimental field evaluation the Cross Target also showed its superiority, with tsetse density reduction reaching 90% 15 months after the initial deployment, whereas densities remained high in the channel where Tiny Targets were deployed.

Conclusions: This study underscores the superiority of the new three-dimensional Cross Target in terms of attractiveness to tsetse flies and its resilience to climatic disturbances as compared with the conventional Tiny Target. The Cross Target presents a promising solution to enhance vector control effectiveness in challenging environments, such as mangroves or other hard-to-access areas, where target maintenance is particularly difficult.

Keywords: Glossina palpalis gambiensis; Cross Target; Efficacity; Mangrove; Tiny Target.

Fig. 1

Location of study areas for the Latin square experiments

Fig. 2

The four models of devices used during our study in four different biotopes. Cross Targets in a mangrove channel (A), Tiny Targets in a harbor (B), Biconical traps in a mangrove–savanna interface (“fassadé”) (C), and pyramidal traps in a forest gallery (D)

Fig. 3

Tsetse fly capture devices. Tiny Target covered with adhesive on which tsetse flies are held (A). Cage on top of a trap in which tsetse flies are caught (B)

Fig. 4

Box plot of tsetse daily catches in the different biotopes

Fig. 5

Evolution of tsetse densities according to the type of targets. Tiny Targets (A) and Cross Targets (B) were deployed along two channels in Boffa (C). Periodically, for 27 months, tsetse flies were captured with sentinel biconical traps to assess tsetse fly apparent density (D). * indicates a significant difference between apparent density in the channel with Tiny Targets compared with the channel with Cross Targets. Significant reduction rates in comparison with T0 are bolded

Fig. 6

Resistance of the material according to the model under field conditions