Have you heard of an ants on the wasps that feed on insects to kill the crabs that keep the forest healthy on Christmas Island? Yes, you did not hear it wrong, because it has not happened yet, but this is a worth telling story.
In the next few weeks, Park Australia will release a 2mm Hornets at Christmas Island to control Taiwan’s yellow insane ants. Crazy ants are a big threat to the island’s wildlife, including its famous Red Crab.
Biological Control – When we use a species to control the invasion of another notorious Australian cane toad. So, how do we know about this work?
Christmas Island and its crabs
Christmas Island is a unique natural habitat with many endemic species. The national park covers two-thirds of the island, which has been referred to as the Galapagos of the Indian Ocean.
Many people are aware of the red crabs whose mass migration to the sea has been described as one of the wonders of the natural world.
Christmas Island has many other kinds of crabs, including the impressive bandit crabs. These may be the largest terrestrial arthropods.
These rich lands allow crabs to use the fallen leaves of the forest to preserve the caves and prevent the soil from becoming tight and create an open and diverse forest. But this thriving natural system breaks when the invading ants become rich on the island.
In the early 20th century, yellow crazy ants (Anoplolepis Ding Feng) found Christmas Island. Now these ants form super ant colony, billions of people in hundreds of hectares.
Crazy ant sprayed formic acid on the eyes and legs of the crabs, dealing with them. Crabs soon die and become ants food.
In some cases, crabs live in areas where free insane ants die during their annual migration, so do not go back to the virgin forest. This has produced the continent and even ants did not live.
With fewer crabs, the forest has become less diverse, dense foliage and compacted soil due to the collapse of crab caves. African snails and other invasive species have become common crabs refused.
Park Australia has been in many different ways from the air to the hand-baiting of anti-yellow crazy ants in Red Crabs.
The effect was severe, with the chemical control program starting in 2001 for the super ant colony. This project has slowed the decline of the crab population but is both expensive and time-consuming, so researchers began to consider other options, including the use of other species.
The bug: a scale insect
Super-colonies of yellow crazy ants require a reliable food source and this is provided by yet another invasive species: the yellow lac scale insect (Tachardina aurantiaca).
Scale insects (a type of true bug) suck the sap of trees and produce a sweet secretion from their anal pore called honeydew, which ants then harvest.
It seems that the super-colonies of these crazy ants could not survive without the carbohydrate-rich honeydew provided by abundant scale insects in a patch of forest.
There is evidence that the scale insects increase ant reproduction and make them more likely to attack other species. One large field experiment demonstrated that if we stopped the ants getting access to the scale insects, ant activity on the ground fell by 95% in just four weeks.
The scale insects may need the ants as much as the ants need the scale insects. Some ants protect the scale insects in the same way that humans protect their livestock, by chasing away other predators.
The interaction between these two invasive species has allowed them to build their populations to extremely high densities, something known as invasional meltdown.
The good news is that scale insects, unlike ants, are amenable to biological control. For instance, Australian lady bugs were spectacularly successful in controlling the cottony cushion scale in North America.
Search starts to find a species that can control scale insects on Christmas Island. We found that a small wasp called Tachardiaephagus somervillei, attacked the yellow lacerate in Southeast Asia.
This hornet spawns females in mature female scale insects and kills them from the inside, producing more hornet eggs. This hornet (and other predators) is very effective, yellow lac scale insects are rare in native habitat.
The most important thing is that we have to test whether the Hornets attack other species. Researchers in the field have done this in Malaysia, an unusual approach that has yielded good results. Scientists are exposed to eight-scale insects that are closely related to the Hornets and have not been harmed.
This proves that there is no other scale insect population at Christmas Island that is at risk if the Hornets introduce, in addition to another introduction to the scale insect pests.
The researchers also checked that the Hornets would still work when the scale insects were yellow-mad ants – and they were also often attacked. After years of research it is exciting to release the Hornets on Christmas Island.
Postscript: the toads
We all know the wrong story of biocontrol. The introduction of control sugar cane beetles in Australian sugar cane toads is counterproductive. In Hawaii, the introduction of the mongoose control mouse failed because the mongoose was active during the day, and the mice at night were active. Introduced in these two cases, these species do not have enough research.
But these examples change the rules around the introduction of the species and the law. Today the government is more aware of the risks of invasive species. Strict experiments and risk assessments need to be introduced before the occurrence.
In this case, researchers at La Trobe University worked closely with Park Australia and the Malaysian Forest Institute to collect enough data to meet the Australian government.
We believe this is the most closely watched bio-control project in Australia. When the Hornets arrive in Christmas Island in a matter of weeks, we believe this will set a conservation best practice.
Only the reduction of ants, there will be more healthy crabs, healthy trees, fewer African snails and better soil. It will save money to spend on expensive protection work.