Comparative efficacy of BG-Sentinel 2 and CDC-like mosquito traps for monitoring potential malaria vectors in Europe
Authors: Bertola Michela , Fornasiero Diletta , Sgubin Sofia , Mazzon Luca , Pombi Marco , Montarsi Fabrizio 
Published: May 2022

Abstract
Background
Different trapping devices and attractants are used in the mosquito surveillance programs currently running in Europe. Most of these devices target vector species belonging to the genera Culex or Aedes, and no studies have yet evaluated the effectiveness of different trapping devices for the specific targeting of Anopheles mosquito species, which are potential vectors of malaria in Europe. This study aims to fill this gap in knowledge by comparing the performance of trapping methods that are commonly used in European mosquito surveillance programs for Culex and Aedes for the specific collection of adults of species of the Anopheles maculipennis complex.

Methods
The following combinations of traps and attractants were used: (i) BG-Sentinel 2 (BG trap) baited with a BG-Lure cartridge (BG + lure), (ii) BG trap baited with a BG-Lure cartridge and CO2 (BG + lure + CO2), (iii) Centers for Disease Control and Prevention-like trap (CDC trap) baited with CO2 (CDC + CO2), (iv) CDC trap used with light and baited with BG-Lure and CO2 (CDC light + lure + CO2). These combinations were compared in the field using a 4 × 4 Latin square study design. The trial was conducted in two sites in northeastern Italy in 2019. Anopheles species were identified morphologically and a sub-sample of An. maculipennis complex specimens were identified to species level by molecular analysis.

Results
Forty-eight collections were performed on 12 different trapping days at each site, and a total of 1721 An. maculipennis complex specimens were captured. The molecular analysis of a sub-sample comprising 254 specimens identified both Anopheles messeae/Anopheles daciae (n = 103) and Anopheles maculipennis sensu stricto (n = 8) at site 1, while at site 2 only An. messeae/An. daciae (n = 143) was found. The four trapping devices differed with respect to the number of An. messeae/An. daciae captured. More mosquitoes were caught by the BG trap when it was used with additional lures (i.e. BG + lure + CO2) than without the attractant, CO2 [ratioBG+lure vs BG+lure+CO2 = 0.206, 95% confidence interval (CI) 0.101–0.420, P < 0.0001], while no significant differences were observed between CDC + CO2 and CDC light + lure + CO2 (P = 0.321). The addition of CO2 to BG + lure increased the ability of this combination to capture An. messeae/An. daciae by a factor of 4.85, and it also trapped more mosquitoes of other, non-target species (Culex pipiens, ratioBG+lure vs BG+lure+CO2 = 0.119, 95% CI 0.056–0.250, P < 0.0001; Ochlerotatus caspius, ratioBG+lure vs BG+lure+CO2 = 0.035, 95% CI 0.015–0.080, P < 0.0001).

Conclusions
Our results show that both the BG-Sentinel and CDC trap can be used to effectively sample An. messeae/An. daciae, but that the combination of the BG-Sentinel trap with the BG-Lure and CO2 was the most effective means of achieving this. BG + lure + CO2 is considered the best combination for the routine monitoring of host-seeking An. maculipennis complex species such as An. messeae/An. daciae. The BG-Sentinel and CDC traps have value as alternative methods to human landing catches and manual aspiration for the standardized monitoring of Anopheles species in Europe.

Graphical abstract