Integrating Citizen Science and Field Sampling into Next-Generation Early-Warning Systems for Vector Surveillance: Twenty Years of Municipal Detections of Aedes Invasive Mosquito Species in Spain

Abstract

The spread of the invasive mosquitoes Aedes albopictus, Aedes aegypti, and Aedes japonicus in Spain represents an increasing public health risk due to their capacity to transmit arboviruses such as dengue, Zika, and chikungunya, among others. Traditional field entomological surveillance remains essential for tracking their spread, but it faces limitations in terms of cost, scalability, and labor intensity. Since 2014, the Mosquito Alert citizen-science project has enabled public participation in surveillance through the submission of geolocated images via a mobile app, which are identified using AI in combination with expert validation. While field surveillance provides high accuracy, citizen science offers low-cost, large-scale, real-time data collection aligned with open data management principles. It is particularly useful for detecting long-distance dispersal events and has contributed up to one-third of the municipal detections of invasive mosquito species since 2014. This study assesses the value of integrating both surveillance systems to capitalize on their complementary strengths while compensating for their weaknesses in the areas of taxonomic accuracy, scalability, spatial detection patterns, data curation and validation systems, geographic precision, interoperability, and real-time output. We present the listing of municipal detections of these species from 2004 to 2024, integrating data from both sources. Spain's integrated approach demonstrates a pioneering model for cost-effective, scalable vector surveillance tailored to the dynamics of invasive species and emerging epidemiological threats.

Keywords: Aedes; citizen science; disease; field sampling; invasive; mosquito alert; surveillance; vector.

Figure 1

Map of Spanish municipalities with reported detections over the period 2004–2024 of Ae. albopictus alone (N = 1699, red), Ae. japonicus alone (N = 43, green), overlapping detections of Ae. albopictus/Ae. japonicus (N = 68, ochre), Ae. aegypti alone (N = 2, blue), and overlapping Ae. albopictus/Ae. aegypti (N = 1, black). Map reference: BDLJE CC-BY 4.0, National Geographic Institute—Canary Islands displaced from their actual position.

Figure 2

Twenty years of Ae. albopictus in Spain: cumulative number of affected inhabitants (blue line, transformed by a factor of 1 × 10⁻⁴ for ease of visualization), cumulative occupied area in square kilometers (purple line, transformed by a factor of 1 × 10⁻²), and cumulative number of municipalities (red line). The dot series refers to the secondary vertical axis (right) and shows the number of newly infested municipalities per year. The first detection of invasive mosquito species was in 2004 and the start of Mosquito Alert activity in 2014 is indicated by the vertical dashed line.

Figure 3

Detections of Ae. albopictus by any strategy, broken down by year of first detection. Darker shades indicate earlier detections, starting 2004 up to 2024. Map reference: BDLJE CC-BY 4.0, National Geographic Institute—Canary Islands displaced from their actual position.

Figure 4

Population density (log₁₀ transformed) of Spanish municipalities colonized by Ae. albopictus, by year of detection. The red dashed horizontal line marks the overall mean population density across all municipalities, serving as a reference point for urbanization level. Jittered blue and black dots represent individual municipalities, providing a view of the underlying data distribution. Asterisks indicate the level of statistical significance for the test, showing whether the detected municipalities had significantly higher population density than expected by chance (p < 0.05).

Figure 5

Records of Ae. albopictus, categorized by surveillance strategy (blue: field sampling 2004–2024, red: citizen science 2014–2024, ochre: simultaneous reports from both sources). Map reference: BDLJE CC-BY 4.0, National Geographic Institute—Canary Islands moved from their actual position.

Figure 6

Number of municipal detections of Ae. albopictus per year and strategy (2004–2024). Blue: field sampling, red: Mosquito Alert, gray: simultaneous discoveries. Inset: the bar sections represent the proportion of each class along the whole study period.

Figure 7

Comparison of distances between detections of Ae. albopictus obtained through citizen science and field sampling (2004–2024) (N = 1476).

Figure 8

Geographical distances between municipalities at their first detection of Ae. albopictus and the nearest positive municipality for the species up to the previous year, over the entire period 2004–2024 (blue line: new municipality detected by field sampling; red line: new municipality detected by citizen science; simultaneous discoveries not displayed). The Canary Islands are excluded from the analysis and not displayed. Map reference: BDLJE CC-BY 4.0, National Geographic Institute.