Fig. 2

a Map of Lazio region showing the municipalities in red (dark grey in the monochrome version) (n = 281) where Aedes albopictus surveillance should be carried out according to the national plan for the surveillance and response to arboviruses (PNA), namely those municipalities with a mean altitude < 600 m above sea level (asl). The boundaries of municipalities with on-going surveillance (n = 24) have been highlighted in orange (light grey in the monochrome version). The remaining municipalities with a mean altitude above 600 m asl (n = 97) are in white. b Relationship between the weekly maximum (max) number of eggs laid (MEggs) recorded in each ovitrap (OT) and altitude range, as described by the best-fitting model (exponential decay). Bias-corrected and accelerated confidence intervals (CIs) calculated with 1000 bootstrap replicates are in light green (white in the monochrome version). The grey shaded areas indicate the decreasing abundance of MEggs at increasing altitude till the highest locality where the species was recorded. c Altitudinal and MEggs ranges (in parentheses) according to the exponential decay results, with municipalities in decreasingly intense shades of red (grey in the monochrome version) at increasing altitude (with decreasing MEggs abundance). max Maximum, min Minimum