Optical recognition of the eggs of four Aedine mosquito species (Aedes albopictus, Aedes geniculatus, Aedes japonicus, and Aedes koreicus)

by Nikoleta Anicic, Klaus Steigmiller, Claude Renaux, Damiana Ravasi, Matteo Tanadini, Eleonora Flacio

The continuous expansion of exotic Aedine mosquito species potential vectors of pathogens into new areas is a public health concern. In continental Europe, the surveillance of these mosquitoes is hindered by the simultaneous presence of three main invasive species (i.e., Aedes albopictus, Ae. japonicus, and Ae. koreicus). Standard low-cost surveillance methods (i.e., the deployment of oviposition traps and count of eggs under stereoscopic microscope) fail to distinguish the eggs of the different species. Identification of eggs by molecular methods is costly and time consuming and prevents measuring the density of invasive species and detecting early new invaders. Here we tested whether certain species could be identified by the patterns on the exochorionic membrane of their eggs. In a first step, we examined Aedine eggs of the three mentioned invasive and one indigenous (i.e., Ae. geniculatus) species with a high-resolution stereomicroscope and we identified each egg by MALDI-TOF mass spectrometry. In a second step, we submitted images of the eggs to 60 entomology experts and non-experts and tested their ability to distinguish among the species after an initial short training. The results obtained were consistent. Participants did not encounter difficulties in determining Ae. albopictus and Ae. geniculatus, while they had more difficulties in distinguishing Ae. japonicus from Ae. koreicus. In general, the quality of the exochorion seemed to play a more important role than the expertise level of the rater. The feasibility to differentiate Ae. albopictus from the other two invasive species is a significant achievement, as this is currently the most problematic species at the level of public health in Europe. Due to the presence of multiple invasive species that might prevent the correct quantification of mosquito population densities using standard surveillance methods and due to Ae. aegypti threat, it is recommended to optically determine also other species.