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Crab spider association with the Malagasy pitcher plant Nepenthes madagascariensis Katja Rembold*, Eberhard Fischer, Boris F. Striffler and Wilhelm Barthlott Institute for Integrated Natural Sciences, University of Koblenz-Landau, Universitatsstrasse 1, 56070, Koblenz, Germany, Nees Institute for Biodiversity of Plants, University of Bonn, Meckenheimer Allee 170, 53115, Bonn, Germany and Poststr. 20, 53909, Zulpich-Nemmenich, Germany

Nepenthes madagascariensis is a carnivorous plant which captures its prey in pitcher-like leaves. It is endemic to Madagascar where it occurs along the eastern coast. Altogether 94.3% of its prey animals belong to three taxa: Formicidae (80.2%), Diptera (9.7%) and Coleoptera (4.4%). The prey compositions of the dimorphic lower and upper pitcher types differ significantly, especially in the markedly higher proportion of ants in lower pitchers and the higher number of flying insects in upper pitchers. A comparison concerning the trap frequency of taxa with literature data from Asian Nepenthes species showed that the upper pitchers of N. madagascariensis contained much higher proportions of Coleoptera, Diptera and Lepidoptera; these differences may partly be due to seasonal reasons. No significant correlation could be established between the numbers of prey items with pitcher size. This paper is the first characterization of the prey composition of the little known N. madagascariensis.

The pitchers of Nepenthes madagascariensis are visited by a wide variety of insects attracted to the bright color of the pitcher, the nectar secreted around its opening and the odor of the fluid. The insect visitors appear to become disoriented over time and with increasing likelihood fall into the pitcher and drown. The pitchers form a temporary habitat functional for about three months. Several specialized arthropods including mosquito larvae (Uranotaenia bosseri, U. belkini), mites (Creutzeria sp.), and frit fly larvae (Chloropidae) complete their life cycle in the pitcher and depend directly or indirectly on the drowned insects falling into the pitcher. Colonization by these arthropods varies spatially and temporally between the two forms of pitchers (juvenile, rosette form and adult form). Mites (Creutzeria sp.) show a phoretic relationship in colonizing new pitchers by clinging to adult frit flies that emerge from the pitcher's fluid. Food web interactions in the Nepenthes madagascariensis pitcher are more complex than those reported by Beaver (1985).