Seasonal influence on head capsule deformities in Chironomus zealandicus (Hudson) (Diptera : Chironomidae)

The natural incidence of deformities in the head capsules of Chironomus zea landicus was investigated at four lake sites in the central North Island (N ew Zealand) in summer (December) of 1994, 1995 and 1996, and winter (June) of 1995 and 1996. Significant differences were observed in deformities betw een sites and seasons. Individuals from Hamurana Stream, a relatively clean site, had the lowest incidence of deformities. However, there were still s ignificant numbers of deformed chironomids. The incidence of deformity incr eased in summer in larvae from all sites except Hamurana Stream. No seasona l differences were observed in larvae from Hamurana Stream. There are indic ations that substrate type, season and genetic factors, as well as sediment chemistry may have collectively contributed to the incidence of head capsu le abnormalities in C. zealandicus.