The effects of leaf litter characteristics on feeding and fitness of a tropical stream shredder, Anisocentropus maculatus (Trichoptera : Calamoceratidae)

Plant diversity is high in the tropics, resulting in leaf litter of differing quality in streams that may affect feeding and fitness of shredders. The effects of leaf toughness and nitrogen content on feeding and fitness ( pupal weight) of a Hong Kong shredder, Anisocentropus maculatus (Trichoptera : Calamoceratidae), were investigated in laboratory feeding trials that included leaves from five plant species with contrasting characteristics. Leaf toughness adversely affected the feeding rates and fitness of A. maculatus. Feeding rates on tough leaves (Indocalamus sinicus and Pandanus furcatus) were >96% lower compared with soft leaves (Ficus fistulosa and Liquidambar formosana), whereas feeding rates on moderately tough leaves (Melaleuca quinquenervia) were intermediate. Larval mortality was >7 times higher on tough (78-100%) than softer leaves (0-11%), and resulting pupae were >71% lighter. Leaf nitrogen content was not a good determinant of feeding or fitness of A. maculatus, but larvae appeared to eat greater amounts of nitrogen-poor leaves to compensate for lower food quality. Leaf toughness was the primary determinant of feeding and fitness of A. maculatus, and the refractory leaves of many tropical plants could account for the scarcity of shredders in tropical streams.