Helpful tips on how to deliver mosquito treatments with the greatest chance of success for your customers.

The use of residual pesticide applications on mosquito resting sites has been shown in a wide range of studies to be highly effective in reducing pest mosquito populations. Landing rates have been shown to decrease by as much as 80-90% in properties in the vicinity of high-risk salt marsh areas.1 Despite this evidence for the effectiveness of such treatments, and the well accepted use of this mode of treatment in WHO treatment programs, it is largely an area of untapped opportunity for Australian pest managers. Mosquito treatments utilising surface spray applications can provide a significant revenue stream, as is the case in the US, for example.

Surface residual mosquito treatments are effective when they are applied to all the mosquito daytime resting sites in proximity to the structures and areas to be protected. This is because most mosquito bites arise from these resting mosquitoes when they emerge in the evening, rather than from mosquitoes flying in from elsewhere. Whilst female mosquitoes require a blood feed to lay eggs, mosquitoes mostly feed on plant sugars, so when we treat plant surfaces, we reduce overall adult mosquito numbers.

It usually surprises people to discover that only female mosquitoes drink blood. Adult females need a certain protein found in blood to create eggs before laying them in water. Male mosquitoes lack the mouthparts needed to pierce the skin and access blood vessels. Even for female mosquitoes though, blood is not their primary food source. Like males, they feed on the nectar of plants to secure the sugars they need for energy. (In fact, both male and female mosquitoes are important plant pollinators.) The sugary liquids they consume are stored in the abdomen. In females, the sugars are stored separately from blood.

Residential backyards usually contain a variety of plant species with unique physiological makeups and varying growth rates. This can lead to reduced efficacy of residual spray treatments, especially when high levels of new plant growth occur to create non-treated harbourage for resting mosquitoes. Knockdown of mosquitoes has also been found to vary on different plant species. Despite these concerns, treatments can provide significant reductions in mosquito biting rates in backyards for 4–6 weeks after treatment, with the lower protection period occurring during spring when there is strong new plant growth.

Many species of native and imported plants are found in backyards and in the grounds of hotels and resorts. They display differences in the abundance and arrangement of their leaves, and in the makeup of the cuticular wax in the leaves. Unless a product is applied correctly and it contains a suitable wetting agent structure, the species of plant treated may alter the efficacy of the residual treatment, which in turn will affect the pesticide transfer to the mosquitoes.

The key to success is the selection of the right product and ensuring the application equipment used can execute a thorough application on all surfaces requiring treatment, with a particle size in the range of 150ų. From this perspective, the use of backpack-based mist blowers is proven to provide better coverage.2

Residual pesticide application to vegetation should always be considered as a part of a targeted, integrated mosquito management approach together with the treatment (or removal) of water-holding containers.

A mosquito residual treatment requires applying the pesticide to all the mosquito daytime resting areas within 15 metres of areas to be protected. This includes all vegetation up to a height of five metres, rock walls, shaded areas, around gazebos, eaves, under decks and sub floors, in order to kill the mosquitoes that rest on these surfaces before and after feeding. (There is no need to treat lawns.)

Steve Broadbent, regional director for Ensystex, recommends applying Bithor Dual Action. “Since Bithor contains two active ingredients, from two different chemical classes, it will control even resistant mosquito strains and it ensures effectiveness on a wide range of plant species. The inert components have also all been carefully selected to blend together to ensure the Bithor spreads on a wide range of surfaces to provide even coverage.

“Bithor contains bifenthrin, an axonic toxin, and imidacloprid, a synaptic toxin, and is odourless and non- irritant in use. We recommend application through a mist blower, such as the Birchmeier AS 1200 AccuPower Battery Spray Blower with the REC 15.”

For water harbourages, Mr Broadbent believes they are best treated with a slow release insect growth regulator. “Culithor Granular Mosquito Growth Regulator uniquely uses our ‘Intelligent granular microencapsulation technology’ to provide controlled, long-term prevention of adult mosquito emergence. Culithor can be added directly to the water where the mosquitoes are breeding for quick and effective control, or can even be applied prior to flooding by rain, as it will not be triggered into action until the water floods over it.”

1 Anderson A.L., Apperson C.S., Knake R. 1991. Effectiveness of mist-blower applications to foliage as barrier sprays for salt marsh mosquitoes. Journal of the American Mosquito Control Association. 7:116–117.

2 Trout R.T., Brown G.C., Potter M.F., Hubbard J.L. 2007. Efficacy of two pyrethroid insecticides applied as barrier treatments for managing mosquito (Diptera: Culicidae) populations in suburban residential properties. Journal of Medical Entomology. 44:470–477.

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