symbiotic relationship of a Chironomid with its ephemeropteran host in an Arizona mountain stream

• Published in: Journal of the Kansas Entomological Society 1998-10, Vol.71 (4), p.426-438
• Main Author: Jacobsen, R.E
• Format: Article
• Language: English
• Subjects: aquatic insects; Chironomidae; choroterpes; Ephemeroptera; feeding behavior; host-parasite relationships; infestation; Insect larvae; Instars; larvae; larval attachement sites; Larval development; larval instars; leucrocuta; Midges; nanocladius (plecopteracoluthus); Nymphs; Parasite hosts; Parasites; Parasitism; Pupae; Symbiosis; thraulodes
• ISSN: 0022-8567; 1937-2353

Aspects of the symbiotic relationship of a species of Nanocladius (Plecopteracoluthus) associated with mayfly nymphs in a mountain stream in Arizona are described including its prevalence on three host species, infestation pattern, attachment site selection and feeding behavior. Larvae of this species, designated here as N. (P.) sp. 2, were found primarily on nymphs of Thraulodes sp. (Leptophlebiidae) and occasionally on Choroterpes sp. (Leptophlebiidae) and Leucrocuta sp. (Heptageniidae). Sixty-seven of 116 (58%) Thraulodes sp. nymphs from one collection site harbored from 1-5 N. (P.) sp. 2 larvae (abundance: 0.99 larvae/nymph; mean intensity: 1.72 larvae/host nymph). The range of larval attachment sites on the host became narrower as larvae matured. Most 3rd and 4th instar larvae constructed tubes on Thraulodes sp. that extended from the thorax between the middle and hind coxae posteriorly to the 7th abdominal segment along the lateral margin of the tergites. Pupation occurred within this tube with the pupa oriented posteriorly. The gut contents of larvae and presence of scars at sites of larval attachment on hosts indicate N. (P.) sp. 2 fed upon host hemolymph. Larval feeding and tube construction resulted in gill reduction, or deformation as well as scarring of gill and other body surfaces. However, parasitized Thraulodes sp. nymphs were capable of metamorphosis to adulthood. Dispersion patterns of larvae and pupae across the host population imply intraspecific competition or parasite-induced mortality may limit the parasite's population size. The life stage structure of N. (P.) sp. 2 from this stream suggested the population was not synchronized, but was likely comprised of at least two overlapping generations at the time of collection. Early instars were most abundant on large, late-instar nymphs and on nymphs harboring later midge instars. Late instar larvae of the older cohort tended to be more prevalent on less mature nymphs, suggesting the parasite and/or the host may affect the others' development. Because collections were limited to only one date, the hypotheses presented should be regarded as speculative and tentative until a more extensive study can be performed.