Currently, along the Surf Coast the mosquitos are out in numbers, which can be expected at this time of year after the extended spring rains and with the arrival of warmer weather. However, they are currently in plague numbers, particularly around Anglesea, where they have been able to breed and their larvae grow unhindered by predators in the Anglesea River and particularly in the still waters of Coogoorah Park. This overwhelming inundation of adult mosquitos seems to always follow the acidification events on the Anglesea river where the natural predators of their larvae are effectively removed along with many other aquatic water filtering invertebrates. The micro algal blooms (green water) which follows, gives the mosquito larvae an abundant food source resulting in their fast growth and metamorphosis to adulthood where the cycle repeats after small amounts of mammalian blood has been acquired by the female mosquitoes.
The Surf Coast Shire have been quick to react to the potential mosquito bloom and have been dosing Coogoorah Park for the last 7 weeks with VectoBac granules. VectoBac is a commercially produced aquatic insecticide containing Lysinibacillus sphaericus a bacterium, previously called Bacillus sphaericus, which is commonly found in moist soil and is known for its larvicidal effects. It specifically targets aquatic larvae of Diptera, flies and more specifically the local Southern Saltmarsh Mosquito – Aedes camptorhynchus. It is not known to have any harmful effects on the other aquatic or terrestrial wildlife due to the nature of the bacterium and its mode of action against mosquito larvae.
The current method of application may have limited impact on the Coogoorah Park wetland as the water can be 1 to 2 meters deep and with minimal flow the water column is stratified. Hence, when the pellets sink and dissolve, the bacterium which has a relatively short life span of 10 to 15 days may not transfer back up to the surface layers. It is there where the mosquito larvae do most of their feeding as they breathe at the surface where they are often seen hanging suspended, getting their common name wrigglers as when leaving the surface wriggling down to safety. While it may be more labour intensive, the dissolving of VectoBac or other solution based applications which can be sprayed over the numerous open water channels surface and directly into the feeding zones has proven to be more effective. This was demonstrated after major European flooding when wetlands were sprayed with a similar solution based Larvacide by aerial means to effectively treat the mosquito larvae.
While treating the river and wetlands with a proven larvicide maybe the only way to impact the current mosquito bloom, this larval insecticide does impact many other fly species and their aquatic larvae and possibly other aquatic invertebrates which are all crucial for a healthy balanced wetland ecosystem. The most important challenge to prevent such mosquito blooms in the future is to minimise the impact of these acidification events and resulting loss of the necessary aquatic predators that feed on the larvae. The re- introduction into these wetlands of the native fresh water and estuarine fish species would be beneficial. The neighbouring Painkalac Creek in Airey’s Inlet may include up to 18 fish species or more.
So while these abnormally large mosquito blooms are most likely occurring in and around our rivers and wetlands – the adult female mosquitos are moving back out into the forest, heathland and local urban gardens looking for warm blooded animals, including us, to ingest very small quantities of protein rich blood required to start their reproductive lifecycle.
Please note the male mosquito has no hypodermic mouth parts and does not feed in that way (refer to image).
It is in these environments especially where the forests and gardens are sheltered from the prevailing winds that other secondary controls need to be adopted. Mosquitos do not like citronella or DEET so when outdoors the application of various forms of these repellents can be used to good effect. All stagnant water including pots, ponds and birdbaths are potential mosquito breeding areas and need to be emptied or have the water replenished at least every 3 days or treated with a larvicide agent and replenished every 10 to 15 days to control any wrigglers. Larger fish and frog ponds are best stocked with native fish such as Galaxiella pusilla and Southern Pigmy Perch that can easily control the mosquito larvae all year round.
According to the Entomological Society of Victoria the use of foggers with airborn insecticides has limited and temporary results even when applied over multiple residences given the transient nature of adult mosquitos. This treatment is not species specific and kills many other insect species including pollinators. The other species of insects that are less transient can be impacted for years and the potential for the subsoil ecosystem to be degraded and sometimes even crash when the unseen earth engineers are impacted as these insecticides seep into the ground.
Also, at this time of year there is much breeding and nesting with our avian friends, the birds and micro bats and so depleting their essential food source, the flying insects, results in their decline. So, there are many proven ways to control the local infestation of mosquitos in and around your garden and ways to protect yourself while out walking or gardening. However, we need to think long and hard before we engage the use of foggers which will never be species specific and are proven to have longer term impacts on many other insects and indirectly the natural ecosystems that we all enjoy here on the Surf Coast.
John Lenagan