The ants of Marchena Island, twelve years after the introduction of the little fire ant, Wasmannia auropunctata

Abstract

Marchena is asma]] and isolated island to the north of the Archipelago. The island is largely covered by pyroclastic cones and fresh lava fields. The vegetated area is small (32.8 km2), compared with the size of the island (130 km2). The vegetation is formed by a dry forest dominated by Bursera graveolens (HBK) Trian. & Planch., Croton scouleri Hook.f., Waltheria ovata Cav., Lantana peduncularis Anderss., Opuntia helleri K. Scum., and Castela galapageia Hook.f. (Hamman 1981). Published information refers to only one species of ant being found on Marchena, Camponotus macilentus bidloensis (Wheeler 1919). Lubin (1984) reports three species from this island, but does not mention which species. In 1988, the little fire ant, Wasmannia auropunctata (Roger), was first reported on Marchena by Baert (1988). In a short visit to this island, Baert found some Wasmannia in a campsite in Playa Negra (Fig.1). This is probably the most aggressive species of invertebrate that has been introduced in the Galapagos Islands. Where W auropunctata is found, few native ants and other invertebrates exist (Lubin 1984). There is also evidence that they have an impact on the nesting activities of reptiles and nesting birds (Roque and Causton 1999). Four years after the visit of Baert' s team, Sandra Abedrabbo, a Charles Oarwin Research Station (CORS) entomologist, detected the occurrence of W. auropunctata in two fishing camps, in Playa Negra, Marchena, but she did not determine the area infested. In 1993, the Galapagos National Park Service (GNPS) and CORS began an ant control project in the island, adopting the methodology used in a control project for the same ant species in Santa Fe Island (Abedrabbo 1994). In 1993, the area of infestation of little fire ant was investigated. Bait stations were set up using transects with a grid design to estimate the area of infestation and AMORO applied to control the ants. The area was determined as 5.2 ha. The GNPS carried out a second control trip in 1994 and the ant infestation was apparently reduced to 3.5 ha (Zuniga 1994). Unfortunately, the control program stopped for two years and only in 1996 was it possible to continue it. A GNPS team in 1996 apparently detected a reduction of the area of infestation to between 1 and 1.5 ha (Garcia 1996). In August 1998 (during the El Nino event) and May 2000, we visited the island to determine the status of the W. auropunctata population and to initiate activities to eradicate this species. This paper provides information about its distribution. We also discuss a plan to control this species in Playa Negra, Marchena, and report new island records for the ant fauna of the Galapagos Islands.