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6 February 2007

Terrific Termites

DR TRACEY DAWES-GROMADSKI (CSIRO invertebrate ecologist): This species builds the biggest mounds that you see in northern Australia and the idea here is that the termites not only nest in the mound, but their nest extends underground as well for at least a metre depth. The mound is sort of for defence but it also acts as a sort of silo, for storing a lot of food for them to feed on during the year.

BERNADETTE NUNN: Termites are often wrongly called white ants. They’re totally unrelated to ants, though, like ants, they do live in colonies, with a king and queen producing eggs which end up as either the workers (who usually make up 90% of the colony), the soldiers who are in charge of defence, or the reproductives.

DR DAWES-GROMADSKI: The reproductives actually grow wings so they’re called alates then and then these are actually released upon the first rains of the wet season and you see this mass of termites with wings flying out of the colonies after the first rains and then they’ll just fly around and then pair up with a member of the other sex and then they’ll found a new colony and eventually build a whole new mound.

BERNADETTE NUNN: While some termites are grass harvesters, others live on leaf litter and debris or soil and then there are the wood feeders – although only five percent of all termites are in the pest category.

DR DAWES-GROMADSKI: So these wooden stakes help to sample obviously wood-feeding termites and so we normally put them in the ground vertically and then you pull them up and see if there’s any termites attacking the wood and in this case there has been. It’s only been ten days and they’ve moved in and started feeding on the wood.

These mounds are known as magnetic termite mounds and they’re actually built by a termite species known as Amitermes meridienalis. They actually build their mounds in this sort of characteristic wedge shape and align the thin sort of ridge of the mound in a north-south direction so that’s why they’re called magnetic termites. So when the sun rises in the morning it hits the eastern face, heats it up to a constant temperature. In the midday sun you get no further heating 'cause it’s only hitting that thin ridge. And then by the time the sun moves over the other side in the afternoon, it then maintains the heat on the western face and by that stage the air surrounding the mound has become to a constant day temperature anyway.

So this is another species of termite that we have here in the Territory. And this species is Nesuta termes graviolis and, as you can tell, it nests in trees and their nests are nice and round around the higher branches of the tree and then they build these little runways what we call carton runways that run all the way from the nest, all the way down to the base of the tree. And the idea here is the termites just use them as shelter so they’re not exposed to predators and they’re not exposed to the hot sun so they travel down through these tunnels and that allows them to access food resources on the ground.

BERNADETTE NUNN: There are more than 350 species of termites in Australia - one third of which live here in the Northern Territory. But termites don’t just live in Australia, there are around 3000 species throughout the world. But the greatest numbers of termites and the biggest range of species is in the tropics.

DR DAWES-GROMADSKI: So here in tropical Australia, termites are actually the major decomposer insect. They also play a really important role in conditioning the soil, much like earthworms do, so they help to turn over the soil, to create new soil and to increase the porosity of the soil which helps water penetrate the soil easier rather than running off the surface and leading to erosional problems.

BERNADETTE NUNN: Dr Dawes-Gromadski believes that termites could play a greater role in land rehabilitation. But it’s difficult to just pick up termites and put them wherever you want. So, in this pilot experiment, Dr Dawes-Gromadski is instead trying to find ways to attract termites.

DR DAWES-GROMADSKI: The initial idea is just to take an area that’s quite bare and degraded – so a crusted soil surface, a lot of run-off of water, not much water infiltration – a poor condition site basically. So I’ve got a series of bare plots – 20 in total – and I’m introducing food resources: straw mulch to try and attract grass feeding termites, and wood to try and attract wood feeding termites.

So the idea is we can see what effects just mulching has, what effects the invertebrates have, particularly the termites, and what their combined effects are in trying to restore the health of the soil.

Another thing we’re measuring in these plots is just looking at litter decomposition rates so how quickly the straw mulch actually breaks down. The more termites and the more other bugs you have in the soil, the quicker this mulch is going to decompose and that means the faster the nutrients are going to cycle through the system and help make it healthier.

Traditionally a lot of people look at planting plants obviously but my thought is it’s ok to plant plants but you need to have a healthy soil to plant them in. The bugs in the soil play a really important role in keeping the soil healthy. So when it comes to rehabilitation maybe starting to think about what roles the soil bugs can play as well as planting certain plant species to try and even accelerate further that rehabilitation process.