S. Mahunka szerk.: Folia Entomologica Hungarica 50. (Budapest, 1989)

lemna and in Typha stands Qatter means smaller open areas too), it was inappropriate in Hydrocharis stand. Leaves and leaf-axes were removed from their original position, the surface was much disturbed and according to my impressions, specimens were hidine. In 1988, on the 13th of July, another equipment was tested. It consisted of a net of 25 10x10 cm squares, stretched either by four reed-stalks sticked into the mud or by a floating structure of polyurethane - foam cubes and reed-stalks fixing them (Fig. 1). The Mesovelia specimens were apparently undisturbed by the equipment. Individuals under the 100 square centimeter area were counted, age-class was not recorded. The equipment was used in three types of microhabitats: in the Hydrocharis stand, in the Lemna stand covering alternatively 10-95% (mostly 50-70%) of the water-surface and in the Lemna stand covering 85- 100% of the water surface. Fifty 10x10 squares were counted in the first, 75 in the second and 25 in the third microhabitat. ) Fig. 1: Floating net used in the field estimations Experimental investigation of preference was made with 7 specimens collected in the lacuna and transferred together with vegetation, into a garden. Here a transparent plastic vial 15 cm in diameter was filled with tap water and the water surface was divided into three 8ubequivalent areas: an uncovered water-surface and areas covered by Lemna and Hydrocharis, respectively (Fig. 2*. The number of specimens on each microhabitat was counted every 5 minutes and the vial was turned by 90 degrees so as to exclude the impact of the direction of sunlight and shade of trees. Counting was repeated ten times. In the field the average number of Mesovelia specimens per 100 square centimeters was 0 in the dense Lemna stand, 0. 28 in the less dense Lemna stand and 0. 18 in the Hydrocharis stand. The averages were not significant. Since no specimen was seen on the open water surface, here no estimation was made. In the experimental arrangement the average distribution was as follows: 1. 5 specimens on the open water, 1.9 specimens on the Hydrocharis stand and 3.6 specimens on the Lemna stand. The difference between the average of open water and Hydrocharis was not significant, that between Hydrocharis and Lemna and between open water and Lemna were significant (p <^0.05 and p<r 0.005 respectively*. In the field 1.56 times as many speci-