The importance of habitat structure and environmental variables for the distribution, abundance, and composition of mosquito larvae within the Donaumoos, Bavaria

Peatland rewetting and protection is multifaceted and the laws regulating those measures were established many decades ago. Nowadays, rewetting of peat bogs adds to the set of measures necessary to mitigate climate change effects. However, rewetting is expected to create or increase mosquito breeding sites, thus potentially causing significant changes in their distribution, abundance, and composition. Understanding mosquito populations and their drivers is the key to a successful management strategy upon the occurrence of mosquito-borne diseases. This study investigated the larval populations of mosquitoes within the Donaumoos, a drained peat bog in Bavaria. Sample points were randomly selected in each of the land-use classes (urban, agricultural, vegetated, water body). Larvae were sampled in August 2022 with a 500 µm sieve. Environmental parameters such as water depth [cm], temperature [°C], area coverage of habitat [%], exposure to sunlight, presence of floating debris were recorded. Water samples were analysed (electrical conductivity [µm/cm], water hardness [ppm], pH, dissolved organic carbon (DOC) [mg/L], water turbidity and colour). Amidst drought conditions, only 33 larvae were found, belonging to the species Anopheles maculipennis (n = 28), Anopheles messeae (n = 2), Anopheles claviger (n = 1) and to the genus Culex (n = 2). Highest counts were found in agricultural areas (n = 23) and amongst emergent vegetation (n = 24), especially grasses (n = 24). Out of all larvae collected, eleven were collected on a single day at one sample point: A deep ditch with steep sides and water only at the very bottom, partly shaded by a bridge. To achieve significant results, highlighting the importance of habitat structure and environmental variables for the abundance, and composition of mosquito larvae, sampling needs to be repeated in a more “average” year, which is not prone to drought conditions as 2022.

Sample points positive for mosquito larvae (red) with corresponding abundances within the study area of the Donaumoos throughout August 2022