Accuracy of the automated mosquito counting device BG-Counter 2

Abstract text

The transmission of pathogens is an important capability of mosquitoes. Prevention methods such as the application of insecticides or the removal of potential breeding sites are common practice. However, the timing of their application requires exact knowledge on the spatial-temporal occurrence of the vector species. Mosquitoes are usually collected with CO₂-baited traps and subsequently identified by morphological and molecular biological methods. This procedure is very time consuming, which prevents a short-term assessment of the risk of local mosquito-borne pathogen transmission. Automatic counting traps allow a timely decision-making on the prevention measures against pathogen transmission. The BG-Counter 2 (Biogents) counts insects and discriminates these by size directly in the field. Placed on CO₂-baited traps, captured insects are categorized as "mosquito sized", "too small to be a mosquito" and "too large to be a mosquito". The Counter additionally measures standard environmental parameters, such as temperature and humidity. All information is transmitted to a cloud server at 15-minute intervals. In order to assess the accuracy of this counting device, traps were placed all over Germany which were run in daily and bimonthly intervals. The BG Counter 2 was attached to a CO₂-trap (BG-Trap-Station) and a modified version for gravid mosquitoes. All captured mosquitoes were identified morphologically. The number of mosquitoes were compared to the output of the counter. Spearman correlation coefficients between captured and counted mosquitoes and the counting accuracy was calculated. The correlation varied greatly depending on sampling site (r_s=0,33-0,72). During months with high mosquito abundances, the correlation was also the highest (r_s=0,66). The lowest correlation could be seen in early spring and autumn, during low mosquito abundance months (r_s=0,33). While the BG-Counter 2 can depict the general phenology well, the accuracy during low mosquito abundance is rather low.