Abstract
Vector presence and population dynamics are strongly linked to climatic factors (Chevalier et al., 2004), which consequently can have an impact on the transmission of vector borne diseases. In particular, the abundance of floodwater mosquitoes results from the successive waves of adult emergences due to different flooding of the breeding sites (Becker et al., 2010). Floodwater mosquitoes (e.g. Aedes vexans and Aedes caspius) commonly reach high abundance levels, causing tremendous nuisance in the near and far surroundings, and possibly acting as vectors of arboviruses (e.g. Rift Valley Fever and West Nile viruses). In this preliminary analysis, the abundance of floodwater mosquitoes, determined by field data collections, was compared with Earth Observation data of the same area.
The field data were collected during an intensive and systematic entomological surveillance, carried out in Abruzzo and Molise Regions, as part of the National Plan for prevention, surveillance and response to West Nile and Usutu viruses, and other research projects. The field activity was carried out in four mosquito seasons (2019 – 2022) from May to November; the insect collections were performed weekly or biweekly, using CDC-light traps baited with CO2. Overall, 2,145 collections were made in 60 collection sites and almost 45,000 mosquitoes were morphologically identified, belonging to the 7 genera present in Italy and to 20 different species. Basing on the abundance of floodwater mosquitoes, two collection sites were selected to for this study: Campomarino (Molise Region), where 87.1% of collected mosquitoes belongs to Aedes caspius, and Altino (Abruzzo Region), where Aedes vexans shows its highest abundance. The two sites are close to a marshy area and a river, respectively.
To catch the local characteristics of the possible mosquito breeding sites, the field data collected in two sites were compared with high resolution images by means of the Normalized Difference Water Index (NDWI) trend, using the free web application EO browser (https://www.sentinel-hub.com/explore/eobrowser/) and selecting the time range relevant for mosquito emergence. NDWI index is used to monitor changes related to water content in water bodies, using green and near infrared bands of the electromagnetic spectrum (McFeeters, 1996). Abundance peaks of the two mosquito populations were detected approximately 3 weeks after the increase in water surface, following periods of drought.
This work is a preliminary attempt to use Sentinel-2 data to explain trend/abundance in two mosquito species in central Italy. Limitations due to differences in timing among mosquito collections, satellite passages, cloud coverage, should be considered in further analyses, as well as integration of other data and sources.
Understanding the main drivers leading to abundance peaks of mosquito population would be helpful to focus vector control programs. In this perspective, new insights could derive using new satellite imagery.
References
Becker, N., Petric, D., Zgomba, M., Boase, C., Madon, M., Dahl, C. & Kaiser, A. (2010). Mosquitoes and their control. New York: Springer.
Chevalier, V., de la Rocque, S., Baldet, T., Vial, L., & Roger, F. (2004). Epidemiological processes involved in the emergence of vector-borne diseases: West Nile fever, Rift Valley fever, Japanese encephalitis and Crimean-Congo haemorrhagic fever. Revue scientifique et technique (International Office of Epizootics), 23(2), 535–555. https://doi-org.bibliosan.idm.oclc.org/10.20506/rst.23.2.1505
McFeeters S. K. (1996). The use of the normalized difference water index (NDWI) in the delineation of open water features. International Journal of Remote Sensing, 17(7), 1425-1432. 10.1080/01431169608948714