The tropical fire ant, Solenopsis geminata, is proving to be invincible on Champion Island, one of the two remaining refuges of the critically endangered Floreana mockingbird, Mimus trifasciatus.
This fire ant was first discovered on this small (9.5 ha) island in 2006 by ornithologists, and since then the Galapagos National Park Service has been trying to eradicate the fire ant from the island because of the threat it poses to this rare species of bird. The tropical fire ant has a powerful sting and is known to attack bird hatchlings. It also preys on invertebrates, an important food source for the mockingbirds on this arid island. Mockingbird numbers fluctuate between 20 and 50 individuals on Champion, depending on whether there are favorable environmental conditions. Another 400-500 are found on nearby Gardner Island.
Park rangers preparing bait sticks coated in peanut butter, which has proven successful in previous eradication programs.
Park rangers are using eradication techniques that are known to work on this species of fire ant, but in spite of all their hard work, the fire ant keeps reappearing. It is suspected that the ant is being re-introduced from neighboring Floreana Island where it is common. These ants are strong fliers and it could be that with the help of wind currents, they are flying over the 700 m expanse that separates Champion from Floreana.
Entomologist Charlotte Causton, with funding from Galapagos Conservancy, was able to spend a month in the Galapagos Islands this February working with the Galapagos National Park Service to evaluate the eradication program on Champion, as well as other invasive ants programs in the Galapagos Islands. A visit was made to Champion and the neighboring coast of Floreana and fire ants were found in both places. In fact, the peanut butter-covered sticks that were put out along the coast of Floreana as bait were teeming with fire ants. Studies will need to be made to confirm whether re-introduction is indeed happening. If it is, eradication will not be possible and a new strategy will have to be used to protect the mockingbird.
A bait stick teaming with tropical fire ants, Solenopsis geminata
This is not the first Galapagos island where there have been issues with the re-introduction of fire ants. Fire ants have also island-hopped to the Marielas islets close to Isabela Island, an important breeding site of the Galapagos penguin. Furthermore, because of its capacity to disperse over large areas, this fire ant is hard to control.
One of the recommendations that Dr. Causton will be making is to consider introducing natural enemies of the fire ant from its native range to keep ant numbers below damaging levels – a technique known as biological control. Several species of phorid flies, otherwise known as decapitating flies, are known to attack the tropical fire ant and could be candidates for the job. Closely related species of fly have had success in reducing the impact of the highly invasive red imported fire ant in the US and it is possible that this technique could also be successful in the Galapagos Islands.
Funds are urgently needed to investigate the feasibility of using these flies to control the tropical fire ant, and to assess the safety of using this method of control in the Galapagos Islands.