PREDATOR-PREY INTERACTIONS BETWEEN LARVAL DAMSELFLIES AND MINING LARVAE OF GLYPTOTENDIPES GRIPEKOVENI (CHIRONOMIDAE) - REDUCTION IN FEEDING-ACTIVITY AS AN INDUCED DEFENSE

1. The feeding methods and intensity of predation by larvae of the dam selfly Erythromma najas on leaf-mining larvae of the chironomid Glypto tendipes gripekoveni were examined in artificial habitats differing in complexity. The experiments assessed the influence of chemical stimul i from the predator, light and the concentration of suspended food on the feeding activity of G, gripekoveni inside and outside of the mine. 2. Erythromma najas preyed upon G. gripekoveni as the latter grazed o utside mines. The intensity of this predation decreased significantly at night in a habitat offering alternative prey. 3. When the food conc entration for the chironomid was high, it significantly reduced both f iltering activity and activity outside mines in response to the kairom one produced by E, najas. Feeding activity did not change when food wa s scarce. 4. The induced reduction in filter-feeding and deposit-feedi ng activity probably reduced predator success by reducing the probabil ity of long-distance detection of a mine and location of the chironomi d's hole. 5. The predator can detect and catch mining prey in either t he light (visually) or dark (mechanically). This may explain the lack of diel periodicity in the chemically induced differences in prey acti vity. 6. Reduced feeding activity of mining larvae in the chemically s imulated presence of a larval damselfly can be explained as an induced antipredator behaviour, illustrating the trade-off between feeding de mands and predation risk in a poorly known link of the littoral foodwe b.