Dr Laurie Twigg

Vertebrate Pest Research Services

Forrestfield WA

5 June 2002

Vertebrate Pest Research Services is a section of the Department of Agriculture of WA and has been in existence for over 30 years. It’s been instrumental in developing a lot of control techniques for vertebrate pests in WA - particularly wild dog and fox control, and the control of the rabbit. We’re also involved in house mouse problems, problems with birds such as starlings and native parrots that sometimes cause problems. Over the years we’ve also had a role in exotic disease prevention across Australia.

Currently in Australia there are two biological control options for reducing the impact of rabbits on agriculture and conservation issues. Myxomatosis was introduced into Australia in the early 1950s and its still an important means for regulating rabbit numbers. Over the years it’s become slightly less lethal and some rabbits are evolving resistance. Myxo is a virus which is specific to rabbits. That means it will only affect rabbits and possibly hares in Australia. It is a very good target specific control.

Recently you may be aware that a disease called Rabbit Hemorrhagic Disease, or calicivirus disease, was introduced to rabbit control programs in about 1995 in Australia. And it again is specific to rabbits. However, it’s not been as effective as we thought in all areas, such as high rainfall areas because there was another similar virus there, which impacts upon the ability of the calicivirus to spread across the country in those wetter areas. Nevertheless, RHD and Myxo are still very important biological control for rabbit populations across most of Australia.

With respect to conventional methods of control of rabbits across Australia and particularly in WA, a product called 1080 Oneshot is our main mechanism for controlling rabbits. And with this, every oat in this packet contains 1080 poison, enough to kill about three adult rabbits. That is mixed with about 6kilos of plain oats, which is then laid in a trail in the paddock where the rabbits are a problem. I’d like to point out at this point that there are many controls over whether a farmer can or cannot use 1080. They have to get authorisation from the Department of Agriculture, and they have to demonstrate to us two things. Firstly, that they do have a real rabbit problem, and secondly that there is unlikely to be any environmental impact on other, native animals from a control program. Once they’ve done this they get a voucher and they can go and buy their 1080 poison bait and lay it.

In WA, we’re very fortunate in that we also have plants that naturally produce the toxin in 1080 to stop animal from eating them. And so we have a biological arms race going on between our native plant and animals, which has been going on for at least 30,000years. And what it means is that our native fauna have developed a tolerance to 1080. They are not nearly as sensitive to the poison as introduced animals, like foxes, dingos and rabbits. So we have a very good safety net there for us in using it in Australia.

There is another poison we use on occasion called Pindone. This was developed because at the moment we don’t have an effective antidote to 1080 so you’re not allowed to use it in built up or urban areas. The poison we use there is Pindone. This is an anticoagulant, like the Ratsack you can buy in the supermarket for controlling rats and mice around the home, and it just stops the blood from clotting. And we recommend you use this in urban areas. Or, because 1080 is very water-soluble and easily leaches out of the bait, we use Pindone if people are controlling rabbits over a period where rain is forecast.

1080 is known to be safe, because [as I just said] it leaches out of the bait very easily and we know that there are over 20 species of bacteria and fungi that happily degrade 1080 or use it for energy, and produce – break it down into harmless by-products. 1080 has got a lot going for it in terms of use for pest control.

One of the other advantages we have with 1080 is that there is enough poison left in a poisoned rabbit that it will kill any fox that eats it. This is what we term ‘secondary poisoning’. And so what we urge landowners to do is coordinate their rabbit control programs with their neighbours and also with any fox control that’s done within their area, and that maximises the benefits they get, both from rabbit control and also reducing the impact of foxes on their sheep or lambs.

In many areas in WA, we mainly find rabbits in the coastal heath, sandy habitat. When these areas were cleared for farming, most – or all of our farmers have been very responsible and the areas with sand on them were left uncleared with the native vegetation. However, unfortunately these proved ideal habitat for rabbits – they shelter in these areas and then go out and feed on the pasture. It created quite a dichotomy for the farmers – to work out how to control these rabbits and in some areas it’s meant that some of these areas of native vegetation have had to be degraded to get the rabbits out. The farmers tried to do the right thing by conservation, but unfortunately the rabbits found those habitats ideal.

Despite our efforts to control them, rabbits are still the number one vertebrate pest in Australia. They still have considerable impact on agriculture, and the estimates are anywhere from $600million plus a year losses to agriculture due to rabbits. They also have an impact upon conservation, for example in the arid areas of Australia, as few as 4 rabbits per hectare is enough to stop the regeneration of our native plants. Another effect of rabbit is that they provide a good food source for foxes. Foxes will favour rabbits if they’re there, so an indirect effect is that they help to maintain high fox populations. So in addition to kicking some of the native animals out of their burrows, like bilbies and perhaps some of the burrowing bettongs, they provide food for foxes.

Foxes of course are well recognised for their huge impact on native fauna, although that’s not the sole reason we have lost some of our species. Things like climate change, fragmentation of habitat, etc are also important. However its been well demonstrated in WA through the programs like Western Shield from the dept of conservation and land management that if you control foxes, you get a huge response in the number of native animals.

Foxes seem to be the last nail in the coffin.

We’re also involved in keeping starlings out of WA. A monitoring and destruction program goes on on the WA/SA border. If starlings got into WA proper, they would have a huge impact on our apple and other fruit industries.

So what it is about a rabbit that makes it such a good pest? Firstly it has high fecundity – that is, it can produce a lot of kittens in a year. For example in many areas of Australia, a single adult female will product up to 30 kittens. We’re very fortunate that not all these kittens survive, or we’d have an ongoing very real problem. The other thing about rabbits that makes them a good survivor as a pest is that they don’t need to drink. They get most of their water out of their food, and this enables them to extend right out into the arid zone.

Of course, with a pest like the rabbit, we’re always undertaking further research, and looking for new ways of doing things.

One of the things we’re looking at now is a new technique called ‘Controlling fertility’. Now, one of the advantages of doing this is that all our existing techniques work on increasing mortality or death rate, and that means you have to do them every year or every second year. The advantage with fertility control is that the pest is never there in the first place!

So, if its that good, why aren’t we doing it now? Well up until quite recently we simply didn’t have the technology, and it’s a very difficult thing to achieve, because we want it to be target specific and only affect the pest animals and have no other undesired impact on anything else.

In 1992 a cooperative research centre was set up involving CSIRO, CALM, Dept of Agriculture WA and ANU. The goal is to develop target specific anti-fertility agents for rabbits, foxes, and house mice. How this works is that we fool the pest species into mounting antibodies against their own reproductive systems, so the egg and sperm are coasted with antibodies and conception cant take place. They become almost allergic to each other. 

What that means is that you will reduce the number of offspring produced for the target species …because Australia is so wide, we want that to be spread naturally – we couldn’t go out and do that manually. So that genetic code for that approach will be inserted into a virus which will then transmit our anti-fertility agent for us. In the case of rabbits, it would involve the myxomatosis virus.

The way this would work would be to fool the host into mounting antibodies against its own reproductive tissues. So the egg and sperm become coasted with antibodies and conception cant take place. ie they are almost allergic to one another. Now this response is very similar to what happens to you when you get the cold or flu – you mount antibodies.

In all of this its important realise however that not one thing alone will provide a magic bullet. We need a range control techniques to reduce the impact of vertebrate pests, particularly something like the rabbit. So we see fertility control being an important part of being integrated with our current control strategies. And what it will enable us to do is reduce the amount of poison we need to use, and how often we need to use it. Ultimately, we are needing to destroy much small number of pest species.