Phoretic Associations of Chironomidae (Diptera) on Corydalidae (Megaloptera) in Northwestern Costa Rican Streams

Abstract

Phoretic associations among three species of Chironomidae (Thienemanniella sp. nov., Rheotanytarsus sp. 1, and R. sp. 2) and two genera of Corydalidae (Corydalus sp. and Chloronia sp.) were studied in 13 streams in northwestern Costa Rica that varied in size, elevation, and water chemistry. Thienemanniella sp. nov. seemed to be obligatorily phoretic on Corydalidae larvae, while Rheotanytarsus sp. 1 and R. sp. 2 were also found on other benthic substrates. The number and location of chironomids on megalopteran larvae were assessed over a 9-mo period (February to October). Corydalus sp. was the preferred host for all three chironomid species. Site selection by Chironomidae was related to age of the chironomid (e.g., late instar Thienemanniella were on the thorax while earlier instars were on the abdominal gills). Large megalopteran larvae supported more chironomids than smaller larvae.