Effects of urban building structures on the distribution of breeding sites and ovitrap egg counts of Aedes albopictus in Pfaffengrund, Heidelberg, Germany

BACKGROUND: In recent years, the increased abundance and expansion of the invasive species Aedes albopictus has become a nuisance and health threat in urban areas of Germany. While intensive control and monitoring measures have shown promising results to reduce populations in urban areas, the growing challenges of these measures in newly affected areas have raised concerns regarding cost effectiveness and optimization in efficiency. METHODS: We have used a suburban area (121 ha) with active control measurements in Heidelberg, Germany to study factors that influence the abundance of breeding sites and the number of eggs for Aedes albopictus. As part of control measurements, breeding sites at 1455 land parcels were recorded repeatedly between May and September 2023. In addition, egg counts in 39 ovitraps were recorded. We studied how strongly the effect of control measures on breeding sites was moderated by building type (single-family, terraced, multi-family house). In addition, we analyzed the importance of breeding site availability, proportions of parcels with different building type and the presence of uncontrolled parcels on Aedes albopictus egg laying activity in ovitraps within 100-300 m radius from the trap. Statistical analysis was based on generalized linear models and generalized linear mixed models. We fitted individual models for each buffer size and compared the model performance. RESULTS: Terraced building plots contained the largest number of breeding sites and multi-family house plots the least. A higher share of terraced building plots in the surrounding area was associated with a higher maximum egg count in the ovitraps. In contrast, ovitrap maximum egg counts for Aedes albopictus were lower if the share of uncontrolled building plots in the buffer was higher and if more large breeding sites were present. The best model performance was observed for a buffer size of 200 m. If the temporal variability of the ovitrap egg count data was taken into account, no optimal buffer size could be derived and the effect of breeding site abundance became insignificant. CONCLUSIONS: Our results indicate that terraced house plots are positively associated with breeding site abundance and egg counts of Aedes albopictus in ovitraps. Control measures could be targeted on areas with this building type to increase the efficiency to reduce local breeding opportunities and consequently suppress local Aedes albopictus populations.