02 February 2014

Carpet Die-m: chemical warfare beneath your feet



In which we control wool eating insects.

I like the quote from the Australian philosopher of science Kim Sterelny "Outside the barrier surrounding an [organism], we find a war against all. The space between skins is a no-mans land, controlled by no-one; designed for no-one; littered with the detritus of biological struggle." In some ways this is a little bleak but it also reminds us how good we humans have made our lives relative to most other organisms. We have pushed the constant conflict a little further away. One thing that I liked about the movie Gravity was the sense of the precariousness of life - of only being able to survive in these tiny pockets of air and heat.

It is easy to forget this rather uncomfortable fact as we sit in our lounges, fire on, telly going and a cup of tea in our hands. In fact we don't have to go far to find biological struggle as we sit and sip. One area of conflict is right under our feet. Carpets and rugs, are found in most homes. To most organisms carpets are like wool forests, vast and wide, and they are ready for exploitation. A major issue is that keratin in wool is fairly indigestable and most organisms are not able to make the most of this habitat - which is lucky for us home owners. There are some insects that that can digest wool, like the common clothes moth (Tineola bisselliella) and the Australian carpet beetle (Anthrenocerus australis), and for them those vast expanses of carpets must be like the Serengeti or Great Plains. Left to their own devices these wool-eating communities would grow and continue to cause damage to your carpet.

Inedible to most....
I had a favourite jersey back when I was a teen in the 1980s (hey wool jerseys or jumpers were cool, honestly). My grey jersey went through a lot of adventures with me during the last couple of years at school and at University in Dunedin. When I was unpacking the house after our earthquake rebuild last year I found my old faithful jersey in a box. It was looking much the worse for wear. The clothes moths had been at it and left numerous holes. Clearly that is not something that we would like to happen to our expensive carpets.

Most carpets (and a lot of wool in general) is treated with insecticides (often permethrin)which insects will ingest when eating the carpet and then die. Unfortunately, insecticides often don't absorb into the wool strands that well and will run off in liquids during preparation where it can cause all sorts of problems in an aquatic environment. In most parts of the world there are strict regulations about insecticides and effluents which mean that wool-yarn spinners are not able to adequately protect their yarns. So as part of the ongoing battle in your carpet, researchers have begun to look at other tricks in their chemical arsenal. Matthew Sunderland has just completed his PhD at Lincoln University. He worked with Rob Cruickshank (Lincoln University) and Sam Leighs (AgResearch)
Gratuitous cute kitten shot (but beneath those
paws lies a world of conflict)
 
to develop an alternative to using insecticides. Matthew reasoned that rather than targeting the insects themselves that you could target the wool digestion process inside the insects. Keratin is difficult to break down and wool-eating insects use certain bacteria and protozoa in their gut to digest this protein. Matthew predicted that using antiprotozoal and antifungal (as these also work against protozoa) chemicals, like azole compounds, would kill the gut protozoans in the insect which would stop the breakdown of keratin and the insects would not survive for long in this environment as wool would be just as inedible for them as for most insects.


In a paper in Textile Research Journal, Matthew and his co-researchers report on how they used a variety of azole compounds and a dyebath application to soak the wool from carpet samples with these compounds. They then allowed clothes moths and carpet beetles to browse on these samples and looked at mortality rates. They found that the antiprotozoals and antifungals did indeed kill the insects. They found that these compounds did not
My favourite wool jersey back in the 80s!
soak into wool particularly well but was easily added in carpet shampoos and were effective at killing the insects in very low concentrations. Ultimately there is still a lot of work to do before this addition to chemical warfare will turn up in your home. Targeting protozoan species living in the gut of an insect seems like an effective idea and one which will result in less effluent problems and better protection for wool. So next time you are sitting comfortably in your house, remember that part of the war against all is happening, quite literally, beneath your feet.

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