Natural prey and digestion times of Toxorhynchites rutilus (Diptera : culicidae) in southern Florida

Natural prey of Toxorhynchites rutilus (Coquillett) were identified from gu t contents of 941 larvae collected from treeholes and tires located in an o ak-palm woodland in south Florida. Twenty taxa of aquatic prey were recogni zed in midgut remains, in addition to eggs of Diptera from three families. Ostracods and chironomids were the most abundant aquatic prey in predators from tires, and rotifers and copepods from treeholes. Mosquito larvae accou nted for only 6% of prey items from treeholes and 5% from tires. Remains of terrestrial arthropods of nine insect orders plus mites and spiders were a lso identified, these prey having been captured from the water surface by T . rutilus larvae. An electivity coefficient, R, was calculated for dipterou s prey of each predator instar. Significant heterogeneities among R values in tires were attributable, in part, to high electivity for certain mosquit o species, especially Aedes albopictus (Skuse), and for psychodid larvae, a nd low electivity for larvae of T. rutilus and Orthopodomyia signifera (Coq uillett), a predator-resistant mosquito larva. Diets were more similar betw een predator instars in tires than in treeholes, where invertebrate diversi ty was higher. An associated laboratory study was conducted to determine ho w long common prey could be detected in guts after ingestion. When alternat ive prey were provided immediately after consumption, oligochaetes, copepod s, and psychodid larvae and adults were detected in >50% of dissected T. ru tilus for 8-18 h after ingestion. By contrast, if T. rutilus fourth instars were starved after ingesting test prey, identifiable remains of psychodid larvae were delectable for >30 d in most predator larvae. Thus, the assessm ent of T. rutilus diet by identification of midgut remains is highly depend ent on the consumption of subsequent prey.