Fine-scale temporal and spatial dynamics of Ae. albopictus response to larviciding with Bacillus thuringiensis israelensis in Heidelberg, Germany

The mosquito Aedes albopictus is expanding across Europe, raising concerns due to its ability to transmit arboviruses. The larvicide Bacillus thuringiensis subsp. israelensis (Bti) plays a central role in controlling the spread of Ae. albopictus. The objective of this study is to assess the temporal effectiveness of Bti as a control method using fine-scale spatiotemporal data and a distributed lag non-linear modelling framework. We analyzed 1,320 ovitrap observations from 195 traps alongside records of 4,387 Bti treatments and local environmental conditions for the entire 2023 mosquito season in Heidelberg, Germany. Bti treatments produced a clear reduction in egg counts, with the strongest marginal effects occurring 6–13 days after treatment with efficacy diminishing thereafter at lower treatment counts, while higher counts demonstrated sustained effects. Cumulatively, Bti was highly effective at reducing egg counts even at moderate treatment levels, and a counterfactual no Bti scenario suggested that Bti treatments reduced seasonal egg production by an estimated 41.9% (95% CI 24.4% – 58.5%) and prevented total establishment across the study site. ... mehrThese results demonstrate that Bti can substantially reduce Ae. albopictus populations in urban settings, though its limited temporal efficacy underscores the need for repeated interventions to prevent establishment and spread.