Larval Chironomid Communities (Diptera: Chironomidae) Associated with Establishing Rice Crops in southern New South Wales, Australia

Abstract

Chironomid larvae were sampled sequentially from small experimental rice fields in southern New South Wales, Australia. Sampling was undertaken during the 1995, 1997, 1998 and 1999 crop establishment periods, starting 10 days after flooding (DAF) and continuing at 5 day intervals until 35 DAF. No agrochemical treatments were applied to the fields at any stage. Seventeen species were identified from 3429 recovered larvae. The most abundant species were Chironomus tepperi Skuse (0–91% of 35 day totals), Procladius paludicola Skuse (7–78%) and Polypedilum nubiferum (Skuse) (2–12%). No other taxon accounted for more than 8% of recovered larvae in any year. C. tepperi colonised fields more rapidly than other taxa and, when present, had only a single generation. The abundance of C. tepperi varied dramatically from year to year: from total absence in 1997 to a peak density exceeding 13 000 larvae m⁻² in 1998. Significant differences between post-flood sampling times (R = 0.407, p= 0.009) and between years (R = 0.495, p = 0.001) were found using ANOSIM2 analysis. C. tepperi had a greater impact on community variability at 10 and 15 DAF (42–58%) than any other species, with P. paludicola exerting the most influence from 20 DAF onwards. Exceptionally high densities of C. tepperi in 1998 led to high levels of turbidity, which apparently prolonged the duration of the single C. tepperi cohort by suppressing water temperatures. Comparison of plant densities in the monitored bays to those in nearby bays receiving effective chemical protection shows that rice plant loss increased in response to higher C. tepperi densities. No plant loss occurred in 1997 when C. tepperi was absent, suggesting the other chironomid species present in the fields are not routinely involved in causing significant crop damage.