Seasonal frequency and positioning of parasitic ...

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Title Seasonal frequency and positioning of parasitic midges (Chironomidae) on Pteronarcys biloba nymphs (Plecoptera: Pteronarcyidae)
Author(s) Donna J. Giberson, A. J. MacInnis, M. Blanchard
Journal Journal of the North American Benthological Society
Date 1996
Volume 15
Issue 4
Start page 529
End page 536
Abstract Mature nymphs of Pteronarcys biloba collected from Catamaran Brook, New Brunswick, between October 1994 and October 1995, were hosts to high numbers of parasitic chironomid larvae [Nanocladius (Plecopteracoluthus) undescribed sp., nr, branchicolus]. Nanocladius (P.) sp. has a univoltine life cycle in Catamaran Brook, with emergence occurring nearly simultaneously with the stonefly host in late May and early June. The chironomid larva constructs a silken case on the stonefly nymphs and feeds on hemolymph by piercing the gill tissue or the intersegmental membranes. Stoneflies were collected from different habitat types in 4 stream reaches from the headwaters to the mouth, and the position and number of attached chironomids was recorded for each nymph. The frequency and density of parasitic chironomids was not related to habitat type, but was related to reach; significantly more larvae/host were found in mid-catchment reaches than at the headwaters or mouth (p < 0.05). No parasitized stoneflies were found in the headwater reach, but between 80 and 100% of mature stonefly nymphs collected from the mid-catchment and mouth reaches were parasitized. Mean chironomid densities ((x) over bar +/- SE) were 6.7 +/- 0.4 chironomids/mature host in the fail of 1994 and 3.5 +/- 0.44 in the summer and fall of 1995. Both frequency and density of chironomids were highest on the oldest stonefly age class present; younger stoneflies were also parasitized, but at significantly lower levels. Larval positioning on stoneflies differed with age of larvae; early instar chironomids attached mainly to the thoracic pleura, just under the wingpads, but most migrated to femora by early fall (September), and overwintered on the femora.

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