Temporal patterns of Culex pipiens and Aedes albopictus in northern Italy: the effect of interspecific competition

Aedes albopictus and Culex pipiens larvae reared in the same breeding site compete for resources, with an asymmetrical outcome that disadvantages only the latter species. The impact of these interactions on the overall ecology of these two mosquito species has not yet been assessed in the natural environment. In the present study, the temporal patterns of adult female mosquitoes from both species were analyzed in northeastern Italy, and substantial temporal shifts between abundance curves of Cx. pipiens and Ae. albopictus were observed in several sites. To understand which are the drivers of observed shifts, we developed a density-dependent mechanistic model that takes explicitly into account the effect of temperature on the development and survival of both species. In addition, we included into the model the effect of asymmetric interspecific competition, by adding a mortality term for Cx. pipiens larvae proportional to the larval abundance of Ae. albopictus in the same site. A model calibration was performed through a Bayesian statistical analysis using weekly capture data collected in our study sites in Veneto and Trentino regions in 2014 and 2015. In several cases, our results show that observed shifts were due to the early decline of Cx. pipiens caused by the concurrent rise in abundance of its competitor, and that the competition effect was enhanced by higher abundance of either species. We estimate that competition may reduce Cx. pipiens abundance at some sites up to 75%. However, in some cases temporal shifts can also be explained in the absence of competition between species resulting from a “temporal niche” effect, when the optimal fitness environmental conditions (e.g. temperature, photoperiod) for the two species are reached at different times of the year. These findings demonstrate the importance of taking into account ecological interactions and, in particular, competition between mosquito species in temperate climates, with important implications for the invasion dynamics of the alien species and for risk assessment of mosquito transmitted pathogens, as well as the implementation of effective control measures.