Invasion of the yellow crazy ant - key threatening process listing
NSW Scientific Committee - final determination
The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Invasion of the Yellow Crazy Ant Anoplolepis gracilipes (Fr. Smith) into NSW as a KEY THREATENING PROCESS on Schedule 3 of the Act. Listing of a Key Threatening Process is provided for by Part 2 of the Act.
The Scientific Committee has found that:
1. The Yellow Crazy Ant Anoplolepis gracilipes (Hymenoptera: Formicidae), is notable for its frenetic activity when disturbed (hence its common name) and its long legs and antennae (hence another of its common names, the Long Legged Ant). Workers are monomorphic, body colour yellow-brownish, and weakly sclerotized. Their bodies are 4-5 mm long and slender. The gaster is usually darker than the head and thorax. Queens are approximately 10mm long and much more robust than workers. The crazy ant lacks a sting but subdues and kills prey by spraying formic acid (DEH 2004).
2. The Yellow Crazy Ant is polygynous (multi-queened) and there is no intraspecific aggression among workers. It can form diffuse supercolonies, sometimes extending continuously over large areas (up to 750 ha). Single nests of A. gracilipes can contain upwards of 1 000 queens and tens of thousands of workers. The life cycle of A. gracilipes has been estimated to take 76-84 days (Rao and Verresh 1991). Most dispersal and colony foundation appears to occur through colony budding although winged queens and males have been caught in traps suspended from rainforest trees on Christmas Island, Indian Ocean.
3. The Yellow Crazy Ant is a scavenging predator with a broad diet. It preys on a variety of litter and canopy fauna, from small isopods, myriapods, earthworms, molluscs, arachnids, and insects to large land crabs, birds, mammals, and reptiles (Lewis et al. 1976, Haines et al. 1994, O'Dowd et al. 1999). In addition to these protein-rich foods, Yellow Crazy Ants obtain carbohydrates and amino acids from plant nectaries and honeydew excreted by aphids and scale insects, Homoptera), which are tended on stems and leaves of a wide variety of tree and shrub species (Lewis et al. 1976, Haines et al. 1994, O'Dowd et al. 1999, 2001).
4. The native range of the Yellow Crazy Ant is not known but the species may have originated in West Africa, India, or China (Wilson and Taylor 1967). It has been widely introduced across the subtropics and tropics, including East Africa (2 countries), South and Southeast Asia (9 countries), Australasia (2 countries), and the Indo-Pacific Islands (20 island groups) and Mexico. It is capable of invading both disturbed and undisturbed tropical and subtropical habitats, including urban areas, rural villages, plantations, coastal strand, grassland, savanna, woodland, and rainforest (O'Dowd et al. 2003).
5. The Yellow Crazy Ant has spread across 2500 km2 in the Northern Territory following human-assisted introduction into east Arnhemland (Young et al. 2001). The Yellow Crazy Ant has been intercepted in Australian ports at least 161 times since 1988 (Pest and Diseases Information Database, DAFF). Approximately 40% of interceptions have been in NSW ports. On a national scale, the number of interceptions has increased, with 93% of all interceptions recorded in the period 1988-2002 occurring in the last five years (O'Dowd pers. comm.). This may be due, in part, to increased vigilance. Recently the Yellow Crazy Ant was detected in surveillance traps at Goodwood Island Wharf on the Clarence River near Yamba, NSW.
6. Modelling of the potential distribution using climate matching, suggests that the Yellow Crazy Ant is capable of inhabiting most of northern and north-eastern Australia, from the Kimberley through Darwin, Cape York Peninsula, and down the eastern seaboard of Queensland into coastal and inland parts of northern NSW (Merrin and O'Dowd 2004).
7. The NSW Department of Primary Industries' Biosecurity, Compliance and Mine Safety Directorate and the Department of Environment and Conservation have begun an eradication program using poisoned baits for the infestation of the Yellow Crazy Ant established on Goodwood Island on the NSW North Coast. A similar program on Christmas Island has resulted in successful suppression of supercolonies, although supercolonies continue to form in previously uninvaded areas and require on-going control (DEH 2004, Green et al. 2004). Eradication programs are also underway in the Northern Territory and in Cairns, Queensland.
8. The Yellow Crazy Ant poses a significant threat to biodiversity as the ants have the potential to displace native fauna (Gerlach 2004, O'Dowd et al. 2003, Lester and Tavite 2004). The Yellow Crazy Ant is known to kill invertebrates, reptiles, hatchling birds and small mammals. On Christmas Island, a number of species of endemic fauna, including land crabs, mammals, birds and reptiles, are at risk either directly through predation or indirectly through habitat alteration or resource depletion. Prior to suppression, the Yellow Crazy Ant also had major impacts on the rainforest ecosystem (DEH 2004). Secondary effects were caused by the outbreaks of sap-sucking scale insects that were tended by the Yellow Crazy Ant. This reduced seed production and increased mortality in some canopy tree species (DEH 2004).
9. Species and populations in NSW that may become threatened by the presence the Yellow Crazy Ant include ants such as Rhytidoponera spp., Pheidole spp., Paratrechina spp., Eastern Sedgefrog Litoria fallax, Eastern Grass Skink Lampropholis delicata, and a burrowing skink Ophioscincus truncates (Natrass and Vanderwoude 2001). A range of other ground-dwelling invertebrates and vertebrates may be affected in NSW.
10. In view of the above the Scientific Committee is of the opinion that Invasion of the Yellow Crazy Ant Anoplolepis gracilipes (Fr. Smith) into NSW could cause species, populations or ecological communities that are not threatened to become threatened.
Dr Lesley Hughes
Proposed Gazettal date: 19/08/05
Exhibition period: 19/08/05 - 14/10/05
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