De Groene glazenmaker (Aeshna viridis) in de provincie Utrecht

Jong, T.H. de, 1999. Aeshna viridis in the province of Utrecht (NL). Brachytron 3(2): 11-17. In 1998 localities with Stratiotes aloides (mostly ditches in agricultural land) in the province of Utrecht were surveyed for Aeshna viridis. The species was found at 29 of the 56 visited sites. Oviposition was recorded at nineteen locations. The total number of individuals seen was 75. The maximum number of specimens found at a single locality was eleven. Vegetations with Aeshna viridis were on average more extensive, the water was deeper and the cover of Azolla filiculoides, Elodea nutallii and green algae was less. Homogeneous Stratiotes vegetations with a surface of 400 m² or more and only a slight cover of Lemna spec., Azolla filiculoides and Eloda nutallii, were preferred for oviposition. At such sites, the density of Stratiotes is about 20 plants per m², with leaves protruding at least 15 cm above the water surface. It was observed that females oviposit in all accessible leaves of a single plant before moving on to another plant. They seemed to prefer plants with withered, brown leaf tips. It is suggested that such plants have narrower leaves, which makes them easier to grasp for the female. Besides A. viridis twelve other species of Odonata were seen at the Stratiotes vegetations. Lestes sponsa and Coenagrion pulchellum appear to show a similar habitat preference to Aeshna viridis. In contrast however Erythromma viridulum and Orthetrum cancellatum seem to avoid such localities. Although the leaves of Stratiotes are thought to protect the larvae against predators, fish larger than 10 cm were often found in open spots in the vegetations and fish smaller than 10 cm were even seen between the plants.