FEASIBILITY OF CANE TOAD CONTROL

A central issue for any approach to toad control is its feasibility. We doubt that any of the current methods are feasible in the long term, and have suggested an innovative approach based on the outcomes of TEAM BUFO's research.

On other pages in this website, we’ve explained these new ideas about how to go about controlling toads (see OUR NEW IDEAS page), and how to reduce their ecological impact (see REDUCING IMPACT page).

Would our new approach really work? There are three critical issues: effectiveness, the risk of collateral damage, and logistical feasibility.

Effectiveness

In terms of effectiveness, all we know at the moment is that in laboratory trials and in outdoor experimental ponds, alarm chemicals and parasites kill huge numbers of tadpoles and baby toads (vastly more than you could ever imagine being killed by traps, fences or hand-collecting). It’s hard to see why the same thing won’t happen in the field, but obviously we need to check. The same is true of predator learning – it works well in the lab, so probably will in the field. We haven't tried to "teach" predators in the field, but they learn really quickly in laboratory trials. So, it should work.

Many predators, like this marsupial Dunnart, rapidly learn to avoid cane toads.

Collateral Damage

In terms of collateral damage, alarm chemicals and parasites don't affect native frogs (or any other native animals, so far as we know). So, the risks are very small. The "teacher toads" may well kill some native predators (if the predator is too small and the toad is too big, or the predator is really sensitive to toad poisons) - this is a shame, but these are the animals doomed to die anyway as soon as the toad front arrives. And the "teacher toads" can also help to slow that toad invasion, so will save many other predators.

Logistical Feasibility

Is this scheme logistically feasible? Well, it's a lot simpler than most of the ideas that other researchers have suggested. It’s easy to get hold of the parasites (and we could try to pick virulent strains that kill toads quickly) and to breed them up in a colony of captive toads. Then, all we have to do is infect some toads and release them, to spread the parasite around the new population. Because the parasite can infect toad tadpoles also, we may be able to just put parasites into the breeding pond (this works well in the lab).

The alarm pheromone also shouldn’t be too hard to work with. It can be made from dried toad tadpoles, but ideally we would work out the chemical nature of the molecules involved (our collaborators at the University of Queensland are already doing this) so we could just use synthetic chemicals for this purpose. And producing lots of small sterile male toads isn't as difficult as it sounds. The surgery to sex-reverse toads is simple (see CANE TOAD SEX), and the toads’ huge clutch sizes are a help here. If each sex-reversed "female" produced one clutch of 20,000 eggs (see TOAD BIOLOGY), a colony of 100 such females would generate about two million eggs per year. Not all of those eggs would survive to produce baby toads, but the numbers needed are quite manageable.

Dr. Mattias Hagman conducted many laboratory experiments on cane toad responses to pheromones.

FUTURE CHALLENGES

So, the biggest challenge is going to be actually spreading the parasites, pheromones and infected “teacher toads” out into the wilderness. For this reason, we have designed the scheme for local community involvement. One of the strongest weapons that Australia has in the fight against cane toads is these enthusiastic, well-organised groups of local people – and we need to take advantage of that incredible resource. With their local knowledge, community groups could identify the best places to spread parasites and alarm chemicals (and perhaps "teacher toads" in advance of the front), and then to actually distribute these weapons for toad control.

In addition to the new “weapons” (alarm pheromones and lungworms) that we have discovered for controlling toads, our current work suggests a series of other possibilities as well – and in a number of cases, these dovetail really well with the broad approach outlined above. For example, we are looking at two other pheromones that toads produce – one that attracts tadpoles (and so can be used to trap them out of a pond, or to bring them into close contact with newly-released parasite larvae) and one that may discourage female toads from laying their eggs in a particular pond.

If we can isolate the “discouragement” pheromone, we could use it to concentrate toad breeding in a few ponds rather than have it spread across many ponds - and thus increase the effectiveness of all of our other control methods, as well as use the toads to help control themselves by competition, cannibalism, and the like.

Dr. Michael Crossland and David Nelson conducting experiments on cane toads and native frogs.

So, even though almost all the funding for TEAM BUFO’s research has been for “pure science” (from the Australian Research Council), not for developing methods to control toads, we are really encouraged to see that our scientific discoveries have already identified a new approach to cane toad control – and one that we think will be more effective, and less risky to the native fauna, than any of the other ideas that have been suggested.

We're not claiming that these ideas are the ultimate in toad control - scientific research works by a gradual process of suggesting ideas, testing them, refining them, and so on. But the emergence of these new ideas from our work on the ecology and behaviour of cane toads strongly supports the idea that to control an invasive species, our first step should be to understand it.

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