Council attacks midge masses in summer
Christchurch City Council will spend $300,000 this year trying to control tiny insects plaguing Aranui residents during the summer, but there is no guarantee the measures will work.
Residents living near the council’s wastewater treatment plant in Bromley have been complaining about midges for more than 10 years. They have been forced to keep windows and doors closed and cannot have barbecues outside.
Last year the council stepped up measures to reduce midge numbers and for the first time in several years long time resident Janet Profit was able to enjoy a midge-free Christmas Day. However, the numbers intensified after that and by late-January they were as bad as ever, she said.
Council staff spent the winter developing a midge control strategy and planned on taking further steps to disrupt the different stages of the midge lifecycle in an attempt to reduce the numbers. Council city services general manager David Adamson said in previous years the council’s main form of control was chemical treatment and it would continue with that this year, but alongside other measures.
It would now also cut grass short when midges were likely to settle in it and plant more vegetation to create natural screening to block out light from nearby homes.
Adamson said midges typically emerged from the water at dawn and dusk and were attracted to the nearest light source, which came from the adjacent residential area.
The council also planned to lift and lower the water levels of the ponds to stimulate the midge drying and wetting cycles, which involved trying to dry out the sediment at the bottom of the pond. The midge larvae could not survive in those conditions.
It was also considering dragging specially modified chains along the channel bed to cause physical damage to the larvae – an approach that has been trialled in other parts of the country. The council had budgeted $300,000 for the work this financial year.
Adamson said the council would closely monitor the results through the season and it would adapt its approach along the way.
‘‘We believe targeting the midges at multiple stages of their life cycle should provide a more effective approach.’’
The oxidation ponds provided an ideal habitat for the midges. The ponds were large (240 hectares) and shallow and were exposed to natural ultra-voilet radiation from the sun, which sterilised the bacteria in the wastewater. The nature of the ponds prevented midge predators, allowing them to breed almost interrupted. Profit was doubtful whether the council’s measures would work.