Seasonal Position Patterns and Fate of a Commensal Chironomid on its Fishfly Host

Abstract

Changes in attachment sites of a commensal chironomid, Nanocladius (Plecopteracoluthus) sp. (Diptera: Chironomidae), on the body of its host, Nigronia serricornis (Megaloptera: Corydalidae), were observed in laboratory streams over a 13-week winter period and a 6-week spring period to determine seasonal movement patterns and emergence success. All chironomid commensals were lost from their hosts by the end of the winter study and no emergence was observed. During winter, chironomids resided in the same tube location on hosts for approximately three weeks before changing positions or being lost from hosts. Vacated tubes remained attached to hosts for an average of 3.6 weeks. Eight re-position movements were documented on host bodies and six midges colonized new hosts in the stream. New colonizations occurred most frequently on previously colonized hosts. During spring observations, commensal midges migrated from the abdomen and ventral thorax to the lateral thorax prior to pupation. Emergence occurred between 6 June and 2 July in the laboratory streams. Emergence success was strongly influenced by commensal attachment site when more than one commensal resided on a host, but not when midges occurred singly. Overall, midges exhibited about 4 1 % emergence success. Unsuccessful emergence was attributed to re-attachment failure following a host molt, host death, or unknown causes. These data suggest that commensal midges have high rates of movement after attaching to a host and attachment sites may determine, in part, emergence success.

Infestation intensity and prevalence of an ectosymbiotic midge under variable environmental and host conditions

“…No. 5 (Diptera: Chironomidae) occurs attached to its host, the saw-combed fishfly, Nigronia serricornis Say (Megaloptera: Corydalidae), in all seasons (Pennuto 1998). We have never found this midge free-living.…”

“…It is found attached to hosts in all seasons, constructing a gelatinous tube from which it feeds on particles attached to the surface of the host or its tube. It forms a puparium on the thorax of the host for pupation, and has a peak emergence in May (Pennuto 1997(Pennuto , 1998. Intraspecific competition, possibly for pupation sites, and larval movement behavior have been implicated as important conditions influencing emergence success in this species (Pennuto 2000).…”

Population dynamics and intraspecific interactions of an ectosymbiotic midge in a river in southern Maine, USA

“…The proportion of known commensal ectosymbionts increases to 75% (21 of 28) if only those species associated with other insect hosts are considered. However, neither Bottorff and Knight (1987) nor Pennuto (1998Pennuto ( , 2000 performed behavioral trials to support contentions that midge distribution patterns on hosts resulted from competition. Bottorff and Knight (1987) provided an exhaustive examination of the ectosymbiotic relationship between the midge Nanocladius downesi Steffan (Diptera:Chironomidae) and its stonefly host, Acroneuria abnormis Newman (Plecoptera: Perlidae) in a Michigan, USA stream.…”

“…Twenty-five (69.4%) of the 36 midge species listed by Tokeshi (1993) as forming symbioses with other aquatic organisms are considered commensal. Pennuto (1998Pennuto ( , 2000 also invoked intraspecific competition as a mechanism to explain emergence patterns observed in a laboratory population of a related species, Nanocladius (Plecopteracoluthus) sp. Yet, very little is known of the pop-ulation biology of these symbionts or the intimacy of their relationships with their hosts.…”

“…Several works have shown the frequency distribution of ectosymbiotic midges on their hosts 250 [Volume 22 C. M. PENNUTO does not follow Poisson expectations, either throughout the year or just on some dates (Svensson 1976, 1980, Bottorff and Knight 1987, Jacobsen 1995, 1999, Pennuto 1998, Pennuto et al 2002. The general interpretation from these analyses is that distribution patterns that are overly uniform or clumped on hosts provide evidence of intraspecific competition, or at least evidence of some biological phenomenon other than chance alone.…”