The impact of aerial baiting for control of the yellow crazy ant, Anoplolepis gracilipes, on canopy-dwelling arthropods and selected vertebrates on Christmas Island (Indian Ocean)

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Stork, Nigel E
Kitching, RL
Davis, NE
Abbott, KL
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Large supercolonies of the yellow crazy ant (YCA) (Anoplolepis gracilipes) on Christmas Island (Indian Ocean) have had a major impact on the land crabs on the island, and an aerial baiting programme using Fipronil頷as trialed in 2002 to reduce YCA populations. To assess the potential for non-target impacts of this baiting programme, canopy-dwelling arthropods and selected vertebrates were sampled in four forest treatments: uninfested by YCA; infested but aerially baited several days earlier; infested but hand-baited 12-24 months previously; and, infested but untreated. Canopy arthropods from the lower canopy of five species of tree were sampled immediately after aerial baiting to determine the abundance and diversity of the arthropod fauna in infested and uninfested areas and the potential impact of the insecticide on the arthropod fauna. Relative abundances of terrestrial, diurnal bird species and the nocturnal Christmas Island gecko were estimated at replicate sites within the four treatments in September 2002 and April 2003 to detect the potential for immediate and medium-term effects of the baiting programme on habitat use. Non-baited infested sites and those that had recently been aerially baited showed significantly elevated levels of both YCA and scale insects in the canopy, and the relative abundances of these two taxa were highly correlated. After counts of YCA and scale insects had been removed, no significant differences in the overall abundance of arthropods or the number of orders encountered could be detected across the four treatments. Estimates of relative abundance of vertebrates immediately after baiting indicated that the only sampled species to respond to Fipronil銷as the Christmas Island white-eye, whose abundance was lower in non-baited control areas than in uninfested sites, or aerially baited sites with supercolonies of YCA. The Christmas Island imperial pigeon exhibited a response to baiting when sampled eight months after the initial baiting. The abundance of this species was significantly reduced in the aerially baited sites compared with that in uninfested sites, and overall abundance of this species declined between 2002 and 2003. Although our samples and counts were small, we conclude that, with the exception of reductions in abundance in the imperial pigeon, the immediate to medium-term impacts of the aerial baiting strategy on vertebrates and immediate impact on canopy arthropods were minimal and that, given the importance of control of YCA for the conservation of terrestrial fauna, such baiting programmes should be supported.

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Raffles Bulletin of Zoology

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