Parks Australia has been trying lots of different methods to control yellow crazy ants.
Ant control measures (continued from last month)
Parks Australia has been trying lots of different methods, from aerial to hand-baiting, to reverse the impact of yellow crazy ants on red crabs.
The impact was so severe that a chemical control program targeting the super-colonies began in 2001. This program has slowed the decline of crab populations but is expensive and time-consuming, so researchers began to look into other options, including using other species.
Ants rely on a scale insect for honeydew
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 the ants were denied access to the scale insects, ant activity on the ground fell by 95% in just four weeks.
Scale insect relies on ants for protection
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.
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. (continues next month)
See this article in Tree Fruit Oct 2017
