CITY OF COCKBURN
INTEGRATED MIDGE CONTROL STRATEGY
INTRODUCTION
For some years now, the City has been involved in the control of nuisance midge from
wetlands within the City. To date this has largely centred on North Lake, Bibra Lake and
Yangbeup Lake. Midge swarms from these wetlands occur during the spring and summer
months and result in considerable nuisance to residents living up to a kilometre from these
wetlands. Many of the City’s other wetlands also have substantial potential for the
proliferation of midge with resulting negative effects on surrounding residents.
The midge problem is a major symptom of a much larger problem - that is, the
eutrophication and degradation of urban wetlands. Bibra, North and Yangebup Lakes are
all highly eutrophic, providing ideal conditions for midge to proliferate over other insects
present naturally within the wetland. Once this occurs natural predation of midge by other
insects is limited and midge essentially take over the wetland with their growth boosted by
regular algal blooms upon which they feed. Chemical control therefore must only be
viewed as a short term control measure. The long-term answer is to restore eutrophic and
degraded wetlands to a condition whereby natural ecosystem balance re-occurs such that
midge numbers are essentially controlled as part of an overall natural ecosystem balance.
Past approaches to control have relied largely on the periodic application of larvicide,
mainly Abate to North, Bibra and Yangbeup Lakes from September to February. In late
1994, there has been a development of the midge program allowing more detailed
monitoring to be carried out both before and after treatment and has allowed the initial
development of integrated control strategies which were recognised as being necessary in
order to provide long term solutions to the problem by Council at the time. The program
has also expanded to incorporate the wetlands which may pose future problems as the
result of changes to the catchment area.
The key to providing long term effective control of midge within the City’s wetlands is
therefore considered to lie in the development of a range of integrated control measures
which essentially aim to restore water quality and natural ecosystem balance within the
problem wetlands and to prevent the further degradation of other wetlands within the City.
The purpose of this Strategy is therefore to provide a framework to achieve this long-term
goal whilst reducing the level of nuisance to residents from midge in the short to medium
term. A range of specific strategies have been developed to deal with the issue in an
integrated manner. Issues which are considered important and have been addressed are
wetland water quality, water levels, chemical treatment, research and monitoring, use of
light traps, buffers, revegetation, and community education.
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CURRENT CONTROL STRATEGIES AND ISSUES
The City currently expends in the order of $100,000 per annum on its Midge Control
Program and is leading the way in terms of effort and research in relation to the issues.
The program is focused mainly on the monitoring and larvicidal treatment of problem
wetlands, however a number of other strategies and actions have been developed. A brief
overview of the main areas of activity are as follows:-
Monitoring
Intensive monitoring of Bibra Lake, North Lake and Yangebup Lake is carried out from
September through to March. Bi-monthly monitoring during autumn and winter months is
also carried out. This monitoring is carried out to determine the timing of larvicide
treatments and to assess the effectiveness of treatments. The provision of resources have
allowed the monitoring program to be extended to include bi-monthly monitoring of
potential problem wetlands such as Little Rush Lake, Market Garden Swamps, Lake
Coogee and Kogolup Lake.
These additional resources have also allowed detailed monitoring of water quality and
physical parameters such as water levels and temperature to be monitored on a regular
basis throughout the year. This is providing a much clearer picture in terms of the water
quality and functioning of problem and potential problem wetlands and in time will add
substantially to the understanding of midge ecology within Cockburn’s wetlands.
In addition to larval monitoring and water quality assessment, limited adult trapping is also
being carried out. This is carried out in order to provide information on adult emergence
and distances travelled, which will hopefully provide improved information in terms of
necessary buffer distances, adult midge behaviour and the timing and effectiveness of
larvicide treatments.
Chemical Treatment
Treatment of North Lake, Bibra and Yangebup Lakes is carried out from October through
March with the regularity depending on the results of ongoing monitoring. The regularity of
treatment is at least monthly and is often more regular than this if midge numbers are high.
Improved monitoring and knowledge of the behaviour of midge within our problem
wetlands substantially improved the effectiveness of these treatments, however,
substantial problems are being observed in terms of effectiveness due to what appears to
be a growing resistance to Abate and difficulties which are encountered due to organic
binding of the Abate when algal blooms are present within the wetlands.
Concerns are also held in relation to the impact of Abate on non-target species Australia
wide which will in the long-term place substantial pressure on the use of this chemical
within natural wetlands.
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Development of Alternative Larvicides
The City has been heavily involved in the development of alternative larvicides to Abate for
a number of years. In the past we were major contributors to research carried out to
evaluate an alternative larvicide Sumilarv, BTI and methoprene. The methoprene based
products show substantial promise. This promise has been supported by laboratory and
field enclosure trials.
The City has recently applied to the National Registration Authority to carry out field based
trials for the methoprene products in conjunction with Murdoch University and it is hoped
that should these trials prove successful that registration of the product as an alternative to
Abate will occur in the near future.
Buffers
The City currently has a policy of not supporting the re-zoning of subdivision of land for
residential development within 500m of the edge of any lake that is subject to potential
midge infestation. The Policy also requires development between 500 metres and 800
metres of the lake to have restrictive covenants placed on the title of each new residential
lot warning prospective purchasers that the land may be affected by midge infestation.
This policy has been particularly useful in preventing the exacerbation of midge nuisance
problems for new residential areas within proximity to problem wetlands.
Substantial residential areas however were developed in close proximity to problem
wetlands prior to midge becoming a problem and Council developing its policy, resulting in
substantial areas still being affected.
The policy is considered to be extremely valuable however in minimising impact on future
residential areas surrounding problem wetlands. Problems have been encountered
however with commercial development within the buffers which tends to attract midge
because of high profile lighting and advertising.
Revegetation
The City commenced replacement of fringing vegetation at Yangebup Lake in 1995.
Ongoing revegetation of Yangebup and Little Rush Lakes is planned with a particular
emphasis being on the replacement of fringing vegetation between these wetlands and
existing residential areas. Revegetation has also commenced at other wetlands to reduce
the possibility of midge problems.
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Light Traps
Previous investigations and trials of light traps elsewhere have indicated that they are not
particularly effective in controlling adult midge due to the sheer number of adults which
immerge from problem wetlands. The City has however, installed two light traps at Bibra
Lake and three light traps at Yangebup Lake and are involved in plans to investigate a
possible midge trap utilising renewable energy.
Community Education
Many calls are received by the City’s Environmental Services Section in relation to midge
during the spring and summer months. This is used as an opportunity to educate residents
about the complexity of the problem and provide advice on what practical measures they
can take to reduce the impact on their homes.
A brochure has been produced by the City in conjunction with other Local Authorities
which is to be distributed to residents within the areas affected by midge which is aimed at
fostering an improved understanding of the problem and the types of management
strategies which are required amongst the community. A display for local shopping centres
is also being considered for future use.
Research
The City recently reconvened the Midge Research Group which comprises members from
several other Local Authorities and State Government Agencies as well as Murdoch
University and the Wetlands Conservation Society. The aim of reconvening this group is to
take a co-operative approach to midge research and the development control strategies.
The City also undertakes ongoing research as part of the monitoring program with the
results of research being used to assist in the development of control strategies.
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AN INTEGRATED STRATEGY FOR MIDGE CONTROL WITHIN THE CITY
OF COCKBURN
The development of an overall Integrated Management Strategy for midge within the City
requires the development of individual strategies in relation to the restoration of water
quality, management of water levels, chemical treatment, buffers, revegetation, light traps,
community education and research and monitoring. Objectives and strategies for each of
these areas have been developed and are detailed below. It is considered that the
implementation of these strategies and actions which follow will provide long term
solutions to the midge problem within the City.
The overall aim of these strategies is to reduce the impact of nuisance midge on
residents within the City to acceptable levels via the development of long-term
environmentally sensitive integrated control strategies.
Individually, these strategies are as follows:-
WATER QUALITY
Objective
To restore water quality within eutrophic wetlands such that algal blooms are reduced and
conditions favourable for the proliferation of midge are prevented.
Strategies
 Determine the sources of nutrient input to Bibra, North and Yangebup Lakes and
develop strategies to reduce these inputs and deal with inlake nutrient levels.
 Pursue implementation of nutrient reduction strategies which are developed with
assistance from State Government Departments as necessary.
 Protect water quality within other wetlands which have the potential to create midge
nuisance problems through careful catchment management and water quality control.
WATER LEVELS
Objective
Restore natural water level regime in problem wetlands so as to reduce potential midge
breeding areas and allow occasional drying of lake sediments.
Strategies
 Lobby the Water Corporation and State Government in relation to the pumping of
problem wetlands in order to reduce elevated water levels and allow occasional
summer drying.
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 Ensure that water level regimes in other wetlands which have the potential to create
midge problems are not artificially altered in a manner which will encourage the
proliferation of midge species.
CHEMICAL TREATMENT
Objective
Continue with chemical treatment as a primary control measure, however strongly pursue
the registration of alternative larvicides to Abate which are more effective and have lesser
non-target impacts.
Strategies
 Continue with Abate as an interim measure.
 Aim to phase out Abate as a chemical control measure via the development of
alternative larvicides.
 Carry out field trials of methoprene based products and pursue registration for midge
use should these trials prove effective.
 Continue to push for registration of methoprene and provision of the product at a cost
effective price as an alternative to Abate.
 Investigate the possibility and impacts of carrying out adult fogging as a control
measure.
BUFFERS
Objective
Minimise the impact of midges on residential areas and other sensitive land uses via the
application of suitable buffers to new development adjacent to problem wetlands.
Strategies
 Maintain current buffer policy and review as necessary.
 Improve monitoring of wetlands located within future residential areas to ensure that
potential midge problems are identified well ahead of proposed development.
 Investigate the feasibility of applying midge buffer to commercial development located
within close proximity to problem wetlands.
 Review midge buffer policy as long term measures take effect.
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REVEGETATION
Objective
Re-establish fringing and upland vegetation around problem wetlands where possible to
screen wetlands from residential areas.
Strategies
 Continue to replace fringing vegetation to improve buffering around problem wetlands.
 Ensure that existing fringing vegetation around current problem wetlands and those with
potential to create problems are maintained and enhanced where possible.
LIGHT TRAPS
Objective
Trial the use of light traps at one or more problem wetlands to assess their effectiveness
as a control mechanism.
Strategies
 Trial light traps on problem wetlands and if successful assess the suitability of
expanding the installation at other wetlands.
COMMUNITY EDUCATION
Objective
Raise the level of community awareness in relation to the complexity of the problem, what
measures are being taken to control it and what steps residents can take to reduce the
problem.
Strategies
 Distribute regular information to affected residents in relation to the complexity of the
problem, what the City is doing to combat it, what those residents can do to reduce it
and the importance of catchment management.
 Continue supporting the Midge Research Group website.
(www.cockburn.wa.gov.au/web/midges/)
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RESEARCH AND MONITORING
Objective
Continue and expand current monitoring and research efforts to better understand midge
ecology, improve control measures and assess the impacts of control strategies.
Strategies
 Continue with current monitoring activities and expand to look at impacts of treatment
on non-target species.
 Participate in ongoing research on midge control and ecology through the midge
research group.
 Participate in ongoing research to reduce algal blooms.
The above objectives and strategies provide a framework for decision making and the
development of specific actions in relation to tackling the midge problem in an overall
integrated manner which aims at providing long term solutions to the problem.
Without doing this, the current reliance on chemical treatment is likely to result in ongoing
problems and increased pressure on the City in relation to the application of chemicals
from relevant Government Agencies, the community in general and specific interest
groups.
The development of the above strategies and formulation of actions needs to be viewed in
a medium term timeframe and it is envisaged that this would take in the order of 3 to 4
years.