Ralf Gyselings

The occurrence and ecological requirements of the horse-flies (Tabanidae) of brackish marshes in Belgium

The deteriorated state and shrunken area of brackish marshes in Western-Europe has taken a toll of its typical inhabitants. Careful management of the remaining area is required to conserve the vulnerable biodiversity, yet with respect to the large group of invertebrates we have very poor knowledge on how to achieve this. In this study we investigated the occurrence of horse-flies (Diptera: Tabanidae) in Belgian brackish marshes in relation to habitat properties. We found three strictly halophile tabanid species occurring in Belgium: Atylotus latistriatus, Haematopota bigoti and Hybomitra expollicata. These halophile tabanids are rare insects as their habitat is now rare. Our data indicated that a prime critical condition may be a stable, high groundwater table. In addition, soil salinity probably needs to exceed some threshold, but more data are needed to substantiate this claim. Soil salinity measurements in brackish marshes indicated that soil salinity was significantly higher throughout the year in open, sparsely vegetated patches, compared to fully vegetated marshland. Such conditions could be beneficial to horse-flies or consorts, but have become rare because there is little impetus for maintaining a spectrum of brackish marshland types and associated species. However, maintaining this spectrum is required in order to conserve existing biodiversity in Western-European brackish marshlands.