Galapagos Invasive Species:
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Marchena free of invasive ants: Eradication of introduced fire ants

The field teamThe small fire ant, Wasmannia auropunctata Roger, is probably the most aggressive invertebrate species ever introduced in the Galapagos. This ant has been listed as one of the 100 most dangerous invasive species at a global level by the Invasive Species Global Program. This species was introduced into the islands sometime between 1910 and 1920, and originally colonised Santa Cruz. Since then, it has become established in some of the other islands in the archipelago.

The fire ant was reported on Marchena island for the first time in 1988. It constitutes a serious threat to the fragile Galapagos ecosystems in its negative impact on the native invertebrate communities. In addition, the introduction of this species leads to a decline in reptile and bird populations and also damaging plants as it has a close relationship with the introduced pest, the cottony cushion scale Icerya purchasi.

Marchena, with a total land area of 130 km2 and altitude of 340m, has two vegetation zones, the arid and very arid, together comprising 32.8 km2. In 2000, the Charles Darwin Foundation (CDF) began the eradication programme of the fire ant, working in close collaboration with the park rangers of the Galapagos National Park (GNP). The CDF developed a two-phase methodology:

  1. Monitoring programme of the fire ant and other ant communities using the baits sausage, peanut butter, sweet biscuits and tuna, in addition to pitfall and Berlese traps to estimate relative species abundance and the distribution of the fire ant on the island.
  2. Control programme, using the specific insecticide AMDRO (hydramethylnon 0.73 g/kg) which was dispersed throughout the infested area at the end of each monitoring period.
Broadcasting bait At the start of the programme the infested area was found to be 26 ha, and in this area the number of native species was lower than in uninfested areas. Over the course of the eradication programme the size of the infested area was slowly reduced. In the last monitoring visit in 2002 the infested area had been reduced to a patch 99 m2, while the native invertebrate communities was recovering.

In the monitoring visits carried out by the CDF scientists and GNP rangers in 2003 and 2004, no W. auropunctata were found and the native communities had re-established to an extent comparable to the uninfested area. It is clear that the methods used in the W. auropunctata eradication programme are effective and can be used on other islands where this ant is found.

With these results from Marchena, this year (2004), the GNP has initiated eradication and control programmes against the fire ants W. auropunctata and Solenopsis geminata, at San Pedro on Isabela island, where the infested area is very similar to that of Marchena. They will be using similar methods to that of Marchena, adapted to cope with the denser vegetation found here.

In the future the GNP will carry out fire ant (both species) control and eradication programmes on similar islands to those so far studied, but on a bigger scale. They will continue to monitor the treated islands periodically to ensure that there are no new accidental introductions. The CDF together with the GNP plans to produce a protocol for the aerial application of toxic baits for the treatment of large areas infested by fire ants.

Source: Charles Darwin Foundation and the Galapagos National Park.

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This website was created on 25 October 2004 by PT and JK