Patterns of species diversity and community structure depend on scales larger than just a single habitat and might be influenced by the surrounding landscape. We studied the response of two insect families, mosquitoes (Diptera: Culicidae) and dytiscids (Coleoptera: Dytiscidae), to landscape variables at five spatial scales. We studied adult mosquito and dytiscid abundance, diversity, and species assemblages in relation to water permanence (area of permanent water bodies versus temporary wetlands) and forest cover (area covered by forest versus open land) within nested circles of 100 to 3000 m around trap sites in four wetlands in southern Sweden and in five wetlands in central Sweden. We found that mosquito abundance was greatest in areas with plentiful forest cover and a high proportion of temporary water, while most dytiscids favored open areas with a high proportion of permanent wetlands. However, diversity of both mosquitoes and dytiscids was positively correlated with high permanence and little forest cover. Mosquito species assemblages were mainly influenced by forest cover at a large spatial scale, whereas permanence was more important at local scales. Dytiscid species assemblages were mainly influenced by water permanence, especially at intermediate spatial scales. These results can be explained by the flight capability and dispersal behavior of mosquito and dytiscid species. The observed landscape associations of mosquitoes and dytiscids could be useful when creating new wetlands. Mosquito colonization could be reduced by creating permanent wetlands in an open landscape, which would favor colonization by dytiscids, a potential predator of mosquito larvae, while also supporting the diversity of both taxa.

In southern Sweden, many wetlands have been constructed, and maintaining or increasing biological diversity is often included in the aims. Some wetlands are constructed near human settlements, thus raising the problem of wetlands being associated with mosquitoes (Diptera: Culicidae). Increased biodiversity (including mosquito diversity) is considered desirable, whereas mosquito nuisance from a human point of view is not. Adult mosquito abundance, diversity and species assemblages of constructed wetlands were compared to natural wetlands. The potential of constructed wetlands for mosquito nuisance and transmission of mosquito-borne viruses was evaluated. The study areas included five constructed and four natural wetlands. Mosquito abundance and species richness were higher in the natural than in the constructed wetlands, and showed a positive correlation with wetland size. Mosquito species assemblages formed three clusters, which were not explained by origin, size and water permanence of wetlands. In a redundancy analysis, however, mosquito faunas showed significant relationships with these variables, and size and origin of wetlands were most important. Major nuisance species (multivoltine species feeding on mammals and laying eggs on soil) were found in all wetlands, although in relatively low numbers. Risk assessment for Sindbis virus transmission showed moderate risk for two constructed wetlands near human settlements. It is concluded that small size of constructed wetlands has the advantage of low mosquito numbers from a human point of view. The use of functional groups is recommended as a tool for presenting mosquito data to the public, and for helping communication between scientists and administrative decision makers.

In this thesis, I explore why biodiversity, as exemplified by diving beetle and mosquito faunas, differs between wetlands, and what environmental factors that affect and control diversity in different types of wetlands and landscapes. The study organisms, diving beetles (Dytiscidae) and mosquitoes (Culicidae), are abundant and species-rich groups in many types of wetlands. They also represent predator and prey. I have explored the diversity of diving beetles and mosquitoes along environmental gradients, along which primarily permanence, size, age, and shading, differ between wetlands. I have also studied wetlands in different types of landscapes (urban and agricultural), and in two different geographical regions (SE and SW Sweden). I have studied the colonization process of new wetlands by diving beetles, and changes in their faunas during the ecological succession of wetlands, and also migration and dispersal of diving beetles in different types of landscapes. Finally, I experimentally explored interactions between the predacious diving beetles and a potential prey - mosquito larvae. One important goal throughout the work has been to formulate advices for construction and management of wetlands, to obtain or preserve high biodiversity, both in individual wetlands as well as in whole landscapes. The results illustrate that many types of wetlands: permanent and temporary, small and large, situated in forests and in open environments, new and old ones, support high diversity of the studied organisms. Urban wetlands had generally fewer species than wetlands in agricultural landscapes, but wetlands in both types of landscapes supported unique species. The faunas differed considerably between wetland types, as many species have specific habitat requirements, but it was hard to classify faunas in specific wetland types as more "valuable" than others. Hence, to obtain a rich wetland insect fauna on a landscape level (which should be more important than to maximise diversity in individual ponds), it seems necessary to take into account more than individual wetlands or ponds. It might be vital to maintain different successional stages, and to construct new wetlands (or to rejuvenated later stages), since the early stages are short-lived, and support both rare and unique species not found in later stages. The interaction experiments, among dytiscids and mosquito larvae, showed that diving beetles (middle-sized species, 10-20 mm) significantly reduced levels of mosquito larvae. Single dytiscids could consume large numbers of such larvae. These predators are probably important in the natural control of mosquito larvae.

Field experiments were performed in artificial ponds to evaluate how the density of predatory diving beetles (Dytiscidae) would affect the population levels of mosquito larvae (Culicidae). Mosquitoes colonizing the ponds were predominantly species of the genus Culex. In 2000, most of the dytiscids colonizing the ponds were small (Hydroporus spp.), and these predators had no impact on the size of larval mosquito populations, not even in ponds with added dytiscids. In 2001, larger beetles (Ilybius, Rhantus, and Agabus spp.) were more common, and there were significantly fewer mosquito larvae in ponds with the highest numbers of dytiscids. There was a negative correlation between numbers of diving beetles in the ponds and the mean body length of mosquito larvae. In neither year could dytiscid densities be maintained above a certain level owing to emigration. In laboratory tests, there were marked differences between three common dytiscid species in regard to preferences for Daphnia and Culex species as prey: Colymbetes paykulli Erichson chose mosquito larvae more often, whereas both Ilybius ater (De Geer) and I. fuliginosus (Fabricius) preferred Daphnia spp. All of the tested dytiscids consumed large numbers of prey. Since some dytiscid species can efficiently decrease populations of mosquito larvae, they are probably important in the natural control of these dipterans.

Flying dytiscids were trapped in an agricultural landscape with wetlands in different successional stages and in two urban landscapes with young wetlands. We compared the faunas in air and in water. Hydroporus and Agabus were the most frequently trapped genera in air. Most species were trapped near water in the agricultural landscape, species characteristic of later successional stages were common in air and dominated in water. In the urban landscapes, species were mainly trapped far from water and species known to colonise new waters were common in air and in the youngest waters. Overall, females and immature adults were more common in flight catches during April-July than during August-October. Our results indicate that urbanisation would result in a less diverse fauna, but may lead to an assemblage dominated by species that are infrequent in agricultural landscapes. To obtain a rich wetland insect fauna, a wide range of wetland types is required at the landscape scale.

We investigated diving beetle (Dytiscidae) assemblages in twelve wetlands in an agricultural landscape in southeastern Sweden. Beetles were trapped in wetlands that varied in permanence (temporary or permanent), area (25 to 4,800 m2), age (11 to >50 yr), and shading (open to wooded surroundings). Our objective was to determine if those environmental factors are important in structuring the local assemblages of diving beetles and how the combination of different types of wetlands influence the diversity of diving beetles in a landscape. Generally, species-area relationships were weak, and shaded wetlands, both permanent and temporary, of intermediate size (240-1,100 m2) had the highest richness after a rarefaction analysis. It was not possible to discern a certain type of wetland where diversity was highest (measured by index a and Shannon-Wiener's index), although, again, intermediate sized wetlands did tend to be more diverse than others. Similarities in species compositions were highest among environmentally similar wetlands, and assemblage structure differed substantially between different types of wetlands. Results of ordination (CCA) and variance partitioning revealed that permanence and degree of shading were the most important factors in structuring assemblages. Our findings imply that high diversity of the diving beetles depends on the number of wetland types represented in a landscape. It is possible to achieve high diversity in a small area by combining permanent and temporary wetlands, as well as many age and successional stages, located in wooded and open environments.

The aim in this thesis was to study the importance of different types of wetlands for the biodiversity in a landscape. The landscapes were both agricultural and urban, and wetlands were in different successional stages. Diving beetles (Dytiscidae) were used as study organisms. They are a suitable group for biodiversity studies in wetlands, as they are a species rich group with wide ecological and geographical distribution. I studied diving beetle assemblages and diversity in wetlands and migration (flying dytiscids) among wetlands, and in different landscapes. The species compositions and assemblage structures in air and in water were compared.

Most species and individuals, both in air and in water, were found in the agricultural landscape, the most heterogeneous landscape studied. The species trapped in air were known to be good migrants and the species in water were characteristic of wetlands in later successional stages. Different species dominated in air and in water. It was not possible to specify and predict wetland types that had rich or poor diving beetle faunas. High and low diversities were found along all the studied environmental gradients. However, permanence and degree of shading of the wetlands were important in structuring the assemblages in water. In the urban, more homogeneous landscapes, fewer and other species were found both in air and in water. Many of the species were characteristic of new wetlands and the same species dominated both in air and water. In landscapes with wetlands of recent origins, species that are good flyers and have the ability of migrating long distances should be the earliest colonisers. Gradually they should diminish in abundance or in proportion as other, slower species, colonise the water. This was supported in the studies, as different species dominated in the air and in the water, depending on the landscape structures.

The results may indicate how wetland faunas change when an agricultural landscape gradually tums into an urban area. Urbanisation would imply a species poorer fauna, and other species than in agricultural landscapes. Accordingly, to obtain a rich wetland insect fauna as exemplified by diving beetles, it seems necessary to take into account more than single wetlands or ponds. A series of wetlands in different environments and successional stages should be recommended on a landscape scale.