Bayer’s Jeff Einam outlines the issues associated with wasps, suggesting appropriate treatment methods that take into account their aggressive behaviour. 

Wasps are a complex and variant insect from the orderHymenoptera, which also includes bees and ants. The superfamily Vespoidea is one of the largest in Australia with over 5000 species ranging in size from 1-40mm. The colours are usually bright with many black yellow and orange combinations – warning colouration that you should avoid them at all costs (because of their sting). Interestingly, only the females have a sting and the wasps have no branched or plumose hairs on any part of their body.

The family Vespidae contains 324 species of mostly social wasps and is the best known group, as it includes most of our major stinging pest species. The subfamily Polistinae has 34 species and contains two genera of native, colonial paper wasps Ropalidia and Polistes.

Each nest can have from one to many hundreds of individuals, consisting of one fertilised queen and a population of workers (many of which are suppressed queens). The nest structure varies with species but usually consists of layers or combs of papery, waxy material, sometimes with a spiralling structure. To help protect the larval cells from exposure to weather the whole structure is sometimes covered by an extra layer of papery material. The adults typically feed on nectar, but they hunt caterpillars to feed to their larvae and they give a very painful sting in defence of the nest.

Invasive wasps

The Vespinae are a northern hemisphere subfamily with two introduced species in Australia – Vespula germanica (European wasp), which is widespread throughout southern Australia and Vespula vulgaris (common wasp), which is found in Victoria only.

They live in large colonies underground or in cavities in trees or buildings. Nests consist of a paper comb and envelope, built inside of a sub-soil chamber. They feed their larvae on a large range of insect prey but the adults survive on sugary liquids such as nectar from flowers. However, they will take food from human sources such as pet food and soft drinks. Solid food is masticated and fed progressively to larvae in the nest. They are very aggressive with a potent sting and recruit other nest mates to join the attack via pheromone secretions.

What is the first aid for a wasp sting?

Wasp stings are very painful and may hurt for several days. Apply an ice pack to the sting site to reduce the pain and swelling. The ice pack should contain a mix of ice and water. Some sting victims have a hypersensitive reaction and multiple stings over time can cause a massive allergic reaction. This anaphylactic shock may include puffiness of the skin well beyond the sting site or the development of an asthma-like condition, making breathing difficult. In really bad cases the heart may stop beating. If a person known to have a wasp allergy is stung on a limb, the recommended first aid is the same as for snake bite – pressure immobilisation technique and get them to a hospital as soon as practically possible.

Tackling wasp nests

The treatment of wasps should always start with a thorough inspection during daylight hours and inspect everywhere looking for secondary colonies that may exist close by. Wasps will guard the nest or nest entrance but they are generally not aggressive unless you disturb them.

For subterranean nests always consider the best way to approach the nest, causing as little disturbance as possible. You need to estimate how big the nest cavity is, as you must get an idea of how big the nest is in order to effectively treat them. Always plan to have a safe retreat if things do not go well. This is a good time to let everyone know what you will be doing – advise neighbours to stay inside and shut windows, keep the children clear, etc. You can erect warning signs if you think there is any danger to persons in the area (especially if you are on public access land like a park).

Wasps navigate by the sun, so most of them will be at the nest after sunset and tend to be quieter at this time – you have a better chance of achieving maximum kill without being stung. For underground European wasp nests you can use an electric dust blower to pump dust into the entrance. The aim is to fill the nest cavity and ensure an application to as large a surface area as possible.

Bayer Coopex Dust, containing 1% permethrin is highly recommended for nest treatments and is safe for use in wall and ceiling voids and around electrical systems. Coopex Dust does not provide an instant kill, so it is essential that you prepare to protect yourself and others during application, withdraw from the treatment area after treatment and wait to observe the response. Often it is necessary to return the following morning to confirm that the nest has been destroyed.

Jeff Einem, technical and regulatory affairs manager, Bayer Environmental Science

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