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WHAT MITE BE THE PROBLEM?

Whilst dust mites are commonly thought to be the cause of respiratory issues and skin irritations, it may be a surprise to know that storage mites could just as likely be the culprit. 

In recent decades, our houses have become increasingly well insulated. This rise in humidity and temperature in people’s homes has had the unfortunate consequence of creating the ideal conditions for mites. While house dust mites are relatively well known, pest managers may be surprised to know that storages mites are believed to be equally, if not more commonly, found in our homes.

A study published in April 2019 in Experimental and Applied Acarology suggests that storage mite concentrations are underestimated compared to house dust mite concentrations. The researchers from the University of Bourgogne in France developed three new species-specific methods for identifying house dust mites of the most commonly encountered Dermatophagoides genus (D. pteronyssinus and D. farinae) and storage mites (Acarus siro, Glycyphagus domesticus, and Lepidoglyphus destructor).

They sampled dust with electrostatic dust collectors, in the bedrooms, under beds and in the kitchens of patients with known dust allergies. The study showed that storage mite concentrations were higher than house dust mite concentrations and were higher in dwellings of patients with allergies. The researchers also noted that dampness is a major factor in storage mite development and the presence of effective mechanical ventilation can reduce storage mite concentrations four-fold.

With individual mites being the size of a speck of dust and invisible to the eye, understanding their different behaviours is key to gaining control. Although pest managers may be unfamiliar with storage mites, they are a pest species that it pays to know about.

Mites are not insects, they belong to the arachnids (order Acari) so have eight legs. They are wingless, with oval- shaped bodies, and less than half a millimetre in length. Mites multiply in environments of high humidity (over 65% relative humidity) and can tolerate an upper temperature limit of around 37 degrees. They are more commonly found in coastal regions rather than in drier, inland areas. They feed on fungi and are often found in places where mould is established.

Dust mites: key identifiers

Pest species: The most notorious are from the family Pyroglyphidae, with Dermatophagoides pteronyssinus (main picture, above) being the most significant in Australia. These mites are well known for their association with asthma, although interestingly it is in fact the faeces of the mites that are responsible for the antigenicity of dust mites rather than the mites themselves.

Locations: House dust mites thrive indoors in warm, damp environments and feed on shed human skin. These are the mites found in mattresses, blankets, carpets, soft toys and sofas. Don’t forget pets and pet bedding can also be a source of dust mites. D. pteronyssinus is likely to be the species pest managers encounter most frequently, and is more common in humid, coastal parts of Australia.

Visible indicators: Dust mites are not usually in the air and only become airborne during and after dust-raising activities such as vacuuming and dusting. Old pillows, bedding and heavy mattresses are filled with sloughed skin cells but also mites (dead and alive). Pest managers inspecting a property should be alert to signs of poor housekeeping and customers complaining of allergy symptoms e.g. sneezing, itchy eyes, runny nose, etc.

Dust mites ‘swarm’ around houses, migrating as a group in search of moisture (Photo credit: Gilles San Martin)

Storage mites: key identifiers

Pest species: Queensland Department of Agriculture and Fisheries cites three key species. The mould mite Tyrophagus putrescentiae, the grain or our mite, and the straw itch mite Pymotes tritici. All species can cause problems in storage facilities and generally, 2-3 species are present in an infestation.

Locations: Storage mites present a problem to grain storage and agriculture, and also buildings (and homes) where moisture and humidity levels are high, such as in water-damaged buildings. Storage mites require a more humid environment than dust mites, nearer 80% humidity – the level of humidity required for the mould they feed on. High numbers can typically be found in areas of the home with high humidity, as well as in stored food areas. Mites can also occur on plasterboard in moist areas such as wall cavities.

Because of their rapid growth in warm, moist conditions, they usually reach peak numbers during late summer.

Visible indicators: Dense mite populations commonly develop on wall surfaces suffering from fungal growth, which can develop during the winter on cold wall surfaces when in situations of excessive indoor humidity. The mites graze on the fungi, so pest managers who find evidence of mould should also assume that mites are likely present.

Poorly stored food and grains should be a red flag for pest managers, as mites can be present in kitchen floor dust, cupboards, and pantries, especially at commercial sites such as crop storage facilities and bakeries.

When present in large numbers, mites appear as a moving carpet of brown dust and give off a pungent or damp smell. Clients may complain that foodstuffs taste ‘off’ – a result of dead mites entering the food production process.

Tyrophagus putrescentiae, or the ‘mould mite’ (Photo credit: United States Department of Agriculture)

The straw itch mite, is a different beast and actually bites, causing severe skin irritations. These mites can infest any dry foodstuffs (as well as hay and straw), so an infestation should be treated in the same way as other stored product pests: identify the source, throw out infested material and treat the surrounding areas.

Reducing humidity and good hygiene practices will have a significant impact on mite populations in homes, especially on storage mites, but even the cleanest of homes will have some dust mites. For customers susceptible to allergic reactions, treatment of mattresses with a product registered for mite control and the use of mattress protectors can provide effective protection.

Further reading: Reboux, G., Valot, B., Rocchi, S. et al. (2019). Storage mite concentrations are underestimated compared to house dust mite concentrations. Experimental and Applied Acarology. 77. 10.1007/s10493-019-00376-2.

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