FOOD PREFERENCE OF THE TRICHOPTERAN LARVA ANABOLIA-NERVOSA FROM 2 STREAMS WITH DIFFERENT FOOD AVAILABILITY

The food preference of the trichopteran shredder Anabolia nervosa from two streams with different food availability was studied in laborator y preference experiments. One stream was unshaded and had abundant gro wth of the submerged macrophyte Potamogeton perfoliatus. The other was shaded by trees (Alnus glutinosa) and had very sparse growth of subme rged macrophytes. To test the food preference of Anabolia nervosa for terrestrial leaf litter and submerged plants we offered leaves of: con ditioned Alnus glutinosa, fresh green Alnus, conditioned Fagus sylvati ca, fresh green Fagus, and fresh submerged Potamogeton perfoliatus. Fo r both larval populations conditioned Alnus was the most consumed food item, followed by Potamogeton. Larvae from the Alnus-shaded stream pr eferred conditioned Alnus over all other food items, while larvae from the macrophyte stream did not clearly discriminate between conditione d Alnus and Potamogeton. The three remaining food items were largely r ejected. Food items were analyzed for dry matter, organic matter, fibr e, nitrogen, phosphorus and toughness. Preference was not correlated t o any of these food characteristics, but we suggest that they may stil l be important and influence food choice in a complex manner. The stud y indicates that the preference pattern of Anabolia nervosa is not cle arly related to previous feeding habituation. The ability to feed on f resh Potamogeton is, therefore, not acquired by certain populations of larvae through long exposure to this resource in the field. The high preference for fresh Potamogeton suggests that Anabolia nervosa may ac tively select Potamogeton as food even when alternative food sources s uch as terrestrial leaf litter are abundant in the field.