The search began to find a species that could control the scale insect on Christmas Island—and we found it—a tiny wasp known as Tachardiaephagus somervillei, which attacks the yellow lac scale insect in its native South-East Asia. (continued from last month)
The wasp
The search began to find a species that could control the scale insect on Christmas Island—and we found it—a tiny wasp known as Tachardiaephagus somervillei, which attacks the yellow lac scale insect in its native South-East Asia.
This wasp lays its eggs in mature female scale insects and kills them from the inside, producing more wasps that then lay eggs in more females.
This wasp (and other predators) are so effective that the yellow lac scale insect is rare in its native habitat.
Obviously we had to test that the wasp wouldn’t attack other species. Researchers did this in the field in Malaysia, an unusual approach that yielded excellent results. The scientists exposed eight closely related scale insects to the wasp, and none were harmed.
This proves that no other scale insect population on Christmas Island is at risk if the wasp is introduced, with the possible exception of another introduced scale insect that is a pest in its own right.
Researchers also checked that the wasps would still work when the scale insects are being tended by yellow crazy ants—and they still attacked.
After years of research it is exciting to be on the verge of releasing this wasp on Christmas Island.
Postscript: the toads
We all know of biological control stories that went wrong.
For example the introduction of cane toads to control cane beetles in Australia—which backfired spectacularly. In Hawaii, the introduction of mongooses to control rats failed because mongooses are active during the day and rats are active at night.
In both cases those species were introduced without sufficient research. But they changed the rules and laws around introducing species.
Today governments are much more aware of the risks of invasive species. Rigorous experiments and risk assessments are required before any introduction can occur.
In this case, researchers from La Trobe University have worked closely with Parks Australia and the Forest Research Institute of Malaysia to collect enough data to satisfy the Australian government.
We believe that this is the most closely scrutinised biological control project in Australia. When the wasps arrive on Christmas Island, we are confident that this will set an example for best-practice conservation.
Fewer ants means more crabs, healthier trees, fewer African snails and better soil. And it will save money being spent on expensive conservation efforts for years to come.
See this article in Tree Fruit Nov 2017
