Succession and Stratification of Aquatic Insects Inhabiting the Leaves of the Insectivorous Pitcher Plant, Sarracenia purpurea

Abstract

Greenhouse experiments and field collections were used in investigating the ecological relationships of 3 spp. of Diptera, Blaesoxipha fletcheri (Aldrich) (Sarcophagidae), Wyeomyia smithii (Coquillett), (Culcicdae) and Metriocnemus knabi Coquillett (Chironomidae), which inhabit the digestive fluid of the pitcher plant. Only newly opened leaves actively attract and capture insects. As the leaves age, the insect victims slowly decompose and the leaf fluid pH is lowered. Since the leaves of a pitcher plant are of different ages, each leaf differs in its ability to capture insects and in the degree of decomposition of its captured insects. The relative abundance of the insect inhabitants of a leaf depends upon the leaf age, because each insect species consumes captured insect remains at different stages of decomposition. The buoyant larvae of B. fletcheri feed upon newly captured insects floating upon the surface. As the victims decompose, free-swimming W. smithii larvae filter-feed upon the suspended particulate matter. Accumulated insect remains on the bottom of the leaf chamber provide food for M. knabi. Although all 3 spp. feed upon the remains of captured insects, they do so at different times and at different strata within the leaves.