Date of Award
Bachelor of Science Honours
Faculty of Communications, Health and Science
Dr Mark Lund
The eutrophication of wetlands has created ideal breeding and growth conditions for certain species of Chironomidae (midge). In urban areas, high abundances can cause adult midges to become a nuisance to nearby residents. The shallow and often eutrophic wetlands of Perth (Western Australia) provide ideal conditions for the growth of certain Chironomid species, resulting in common nuisance problems. To control nuisance plagues a range of management options are available, including light traps, biological controls, insect growth regulators and pesticides. In Australia, Abate00 is the only registered pesticide for the control of midges. Little is known about the life histories of nuisance species. Current management approaches rely on threshold larval densities as an indication of optimum spray times (with Abate®). This ignores the possibility of exploiting vulnerabilities within the life cycle to provide good control with minimum environmental impact. This project aims to determine the effects of two key factors, temperature and sediment type on growth and survival of two common nuisance species. Eggs of Chironomus alternans and Polypedilum nubifer were collected from the field within 24 hours of laying and reared at 15, 20, 25 and 30°C. Hatching times for C.alternans were 5-5.2, 3-3.5, 2-3 and 2 days for l5°C through to 30°C respectively. Hatching times for P.nubifer were slightly longer at 6, 4, 3 and 2.67 days for l5°C through to 300C respectively. All eggs in this experiment hatched at l5°C to 30°C, implying that the eggs do not act as a resting stage to survive harsh conditions. There were three containers per replicate and three replicates per temperature for the main and sediment experiments. Each container at each replicate was terminated over the course of the experiment. Terminations occurred at 2.5, 3.5 and 4.5-6 weeks for the main experiment and 4.5-6 weeks for the sediment experiment. Terminations consisted of separating the living larvae from the sediment, preserving them and then measuring their head widths and body lengths. Chironomus alternans had highest survival at 20°C followed by l5°C, with very low survival at 25°C and 30°C. Emergence occurred at >51, 32.5, 28 and 26 days at l5°C through to 30°C respectively. In the field, Chironomus alternans emerges in large numbers in spring. Faster larval development resulted in low survival levels. Some larvae were able to survive at 25°C and 30°C, enabling larvae to survive through to the next season. Polypedilum nubifer had highest survival at 20°C followed by 25°C with no larvae surviving at l5°C and 30°C. Emergence only occurred at 30°C at 19 days for P.nubifer. Eggs of P.nubifer were not available for the majority of the experiment, thus preliminary results are presented and further research needs to be done on this summer species. Sediment type and particle size did not affect the survival of larvae. The sediment experiment showed higher survival rates in the coarse (99% ±0.005) and fine sand (88% ±0.12) compared to metaphyton (62% ±0.082) (Figure 6.3.1). Average time to emergence was fastest in the coarse sand, implying that larvae preferred those conditions. Although current pesticide usage is adequate to reduce nuisance problems, this study has highlighted some potentially new approaches to the timing of spraying that may increase effectiveness and reduce the number of sprays required. Ultimately nutrient control remains the only long-term way of eliminating or reducing the problem.
Suffell, K. (2002). Improving Management of Nuisance Midges (Chironomidae: Diptera) in Perth (Western Australia) Wetlands Based on Their Response to Temperature and Seditment Type. Retrieved from http://ro.ecu.edu.au/theses_hons/567