Emergence phenology of Chironomus tepperi Skuse and Procladius paludicola Skuse (Diptera: Chironomidae) during rice crop establishment in southern New South Wales

Abstract

Midge emergence from untreated rice bays was monitored with conical traps during crop establishment. Chironomus tepperi Skuse was the numerically dominant species in all 3 seasons of the study, and generally had only 1 generation, although there was some evidence of a minor, non-overlapping second generation in the 1992 season. Emergence of first generation C. tepperi was highly synchronised, with peaks occurring 16-17 days after flooding. Procladius paludicola Skuse became the dominant species in trap collections after C. tepperi emergence declined, and had multiple overlapping generations. Members of the genus Procladius are predacious rather than phytophagous. Chironomus tepperi and P. paludicola together comprised 45.6-80.4% (mean 68.1%) of midges emerging during the first 48 days after flooding. More than 30 midge species were recorded from the trial site, but C. tepperi was the only phytophagous species recorded in sufficient numbers to warrant individually targeted control. Although C. tepperi has, in a practical sense, only 1 generation in establishing rice bays, growers have consistently reported that multiple chemical treatments are necessary to prevent crop damage. There are several possible explanations for this apparent anomaly. Chemical seed treatments may be failing to disperse sufficiently to control the first C. tepperi generation. Also, the elimination of chironomid larvae through the use of seed treatments may be making fields receptive to reinfestation by C. tepperi if oviposition is being regulated by the presence of larval populations. A third possibility is that phytophagous species other than C. tepperi, although poorly represented individually, may sometimes be abundant enough collectively to cause significant crop damage.