483 The Recent Introduction of the Neotropical Tramp Ant Wasmannia auropunctata (Hymenoptera: Formicidae) Into Vanuatu Archipelago (Southwest Pacifie) by Herve Jourdan '. Lydia Bonnet de Larbogne! & Jean Chazeau 1 ABSTRACT We discuss the spread of Wasmannia auropunctata (Roger) into northern Vanuatu and review the implications of this invasion for agriculture and people welfare. We also dlscuss the lack ofknowledge about the Vanuatu ant fauna (only 46 recorded species, in 28 genera) and the threats this invasion is weightng on. The invader was first detectcd on Vanua Lava, Banks Islands, by mid 1998. It now infests more than 1200 hectares on Vanua Lava and netghboring Mota islet. Human mediated dispersion appears to be the principal cause of its spread, as the ant's intrtnstc dispersion capacity is low. An eradication program does not appear to be a realistic goal. given the actual extent ofthe invasion. Slowing the spread of the exotic ant appears to be more feasible and cost effective. Contamment measures are thus recom- mended, such as the interdiction of agrtcultural products exportation from infested areas associated with careful quarantine control in every potential entry point in the archipelago (atrports, harbors and island wharves. nursery plantations ...). These measures necessitate goodwill cooperation of Vanuatu people and should be associated with actions aimed to inform and to educate about the exotic ant problem as well as on the necessity to support the containment measures. Key words: Biological invasion, tramp spectes, exotic ant, ant fauna, distribution. Wasmannia auropunctaia; Homoptera, mutualism, con- trol measures, Vanuatu, South West Pacifie. island. INTRODUCTION Wasmannia auropunctata ts native to the Neotropics where its range encompasses most of the Caribbean area, Central America, to central Mexico and much of South America down to north Argentina and Uruguay (except the Andean region) (Kusnezov 1951, Kempf 1972, Brandao 1991). In lts native range. this myrmicine lives from sea level up to 1000-1500 m (as observed in Columbia. Dommican Republic and 1 Laboratoire Zoologie Appliquée. IRD (ex ORSfOM), BI' A5, 98948 Nouméa Cedex. New Caledonia. Email: [email protected]
Transcript
483
The Recent Introduction of the Neotropical Tramp AntWasmannia auropunctata (Hymenoptera: Formicidae) Into
Vanuatu Archipelago (Southwest Pacifie)
by
Herve Jourdan '. Lydia Bonnet de Larbogne! & Jean Chazeau 1
ABSTRACT
We discuss the spread of Wasmannia auropunctata (Roger) intonorthern Vanuatu and review the implications of this invasion foragriculture and people welfare. We also dlscuss the lack ofknowledgeabout the Vanuatu ant fauna (only 46 recorded species, in 28 genera)and the threats this invasion is weightng on. The invader was firstdetectcd on Vanua Lava, Banks Islands, by mid 1998. It now infestsmore than 1200 hectares on Vanua Lava and netghboring Mota islet.Human mediated dispersion appears to be the principal cause of itsspread, as the ant's intrtnstc dispersion capacity is low. An eradicationprogram does not appear to be a realistic goal. given the actual extentofthe invasion. Slowing the spread of the exotic ant appears to be morefeasible and cost effective. Contamment measures are thus recommended, such as the interdiction of agrtcultural products exportationfrom infested areas associated with careful quarantine control in everypotential entry point in the archipelago (atrports, harbors and islandwharves. nursery plantations...). These measures necessitate goodwillcooperation of Vanuatu people and should be associated with actionsaimed to inform and to educate about the exotic ant problem as well ason the necessity to support the containment measures.
Key words: Biological invasion, tramp spectes, exotic ant, ant fauna,distribution. Wasmannia auropunctaia; Homoptera, mutualism, control measures, Vanuatu, South West Pacifie. island.
INTRODUCTION
Wasmannia auropunctata ts native to the Neotropics where its rangeencompasses most of the Caribbean area, Central America, to centralMexico and much of South America down to north Argentina andUruguay (except the Andean region) (Kusnezov 1951, Kempf 1972,Brandao 1991). In lts native range. this myrmicine lives from sea levelup to 1000-1500 m (as observed in Columbia. Dommican Republic and
Costa Rica) (Fabres & Brown 1978, Longino & Nadkami 1990). It ismainlya terricolous species, nesting in litter (between dead leaves or inrotton wood) either in soil or at the base of trees (especially in the dryseason). Occasionally it nests in dead wood on trees or in tree canopies(Longino & Nadkami 1990; Way & Bolton 1997).
This ant could be described as a minute yellow-brown myrmicine(workers are 1.5 mm in length) and as a slow moving ant. The diagnosiscomprises an antennae 11-segmented. with a 3-segmented club.Antennal scrobes are present. bounded below by a weak longitudinalcarina running above the eyes. Anterodorsal angles ofthe pronotum areacute. the pronotum is strongly marginate anteriorly. Promesonotalsuture is absent. metanotal grove is weakly impressed. Propodeum isbispinose. metapleuallobes are present.
Wasmannia auropunctata: an invasive ant spreading worldwide.During past decades, human activities have spread this tiny stinging
ant, so its distribution is nearly pantropical. Despite the seven subspecies that are currently recognized for W. auropunctata (Bolton 1995), inmost reported invasions. the subspecific name is not specified. According to Kempfs catalogue (1972) and Wetterer & Porter (comm. pers.), itseems likely thatmost or all invasive are W. auropunctataauropunctata.
Little fire ants are now recorded from Cocos island (ForeI1902; Hogue& Miller 1981). Florida (Wheeler 1929). Bermuda (Hilbum et al. 1990),Bahamas (Wetterer & Porter comm.pers.), Cameroon (Bruneau deMiré1969), Gabon (Santschi 1915; Wetterer et al. 1999), Galâpagos(Silberglied 1972; Pezzati et al. 1998), Solomon (on Guadalcanal islandas well as on Sola and Vulelua. but other islands may be affected)(Macfarlane inWaterhouse & Norris 1989; Wetterer 1997), New Caledoniaand nearby Loyalty islands (Fabres & Brown 1978; Jourdan 1997a),Wallis, Alofi and Futuna islands in the Wallis & Futuna archipelago(Gutierrez 1981; Jourdan 1997a), Hawaii (Anonymous 1999), andVanuatu (Tumukon 1999; Rapp 1999). But. it is still spreading in theTropical Pacifie: according to Nishida & Evenhuis (2000), it may havereached Fiji shores. The little fire ant would also present on the coastofSumatra island (Bruneau de Miré pers. comm.), in the coastal regionofPointe Noire in Popular Republic ofCongo (Veysseyre pers. comm.) aswell as in Democratie Republic of Congo (ex Zaire), according to Fowleretal. (1994). W. auropunctatawas also recorded in Califomia (Nickerson1983), but its permanent establishment there appears doubtful (Wardpers. comm.). Several populations have also been recorded from tropicalgreenhouses in different temperate areas (Donisthorpe 1927; Ayre1977; Anonymous 1979; Naumann 1994), but cold winters will prob-
Jourdan, H. et al. - Little Fire Ant Spreads into Vanuatu 485
ably prevent any outside establishment.Because of its painful sting, W. auropunctata is a well known pest in
every place where outbreaks occur. So a wide array of local namescharacterize this ant: "liUle fire ant" for English speaking people,"abdelaya" for Spanish speaking people ("abdelayalde" in Puerto Rico),"tchabe" in Cameroon, "formiga pixixica" in Brazil, "hormiga colorada"in Galapâgos, "petite fourmi de feu" in French West Indies, "fourmielectrique" in New Caledonia or "tsangonawenda" in Gabon (Smith1936; Bruneau de Miré 1969; Delabie 1989; Ulloa Chacon 1990; Jaffe& Lattke 1994; Jourdan 1997b; Wetterer et al. 1999). The species is arepresentative of the "tramp ant" group (Hôlldobler & Wilson 1990;Passera 1994; McGlynn 1999) which exhibits biologieal characteristics(polygyny, unicoloniality, budding of new nest, reduced nuptial flight.opportunism for food and nest location, fast nest relocation afterperturbation) which facilitated its spread through human mediateddispersal.
Origins of invasion into Vanuatu archipelago.Wasmannia auropunctata was first detected in June 1998, in the
Banksisland group, North ofVanuatu (Fig. 1). VanuaLava wasreportedas the first invaded island. According to local informers, the ant hadprobably been introduced in 1994-1995 on building materials. imported by the Melanesia anglican diocese ship, calling from Honiara viaSola, in the Solomon. In Mid 1999, reports assessed its presence onVanua Lava and Mota and mentioned unconfirmed reports of itspresence on Gaua (Tumukon 1999; Rapp 1999).
Our survey focussed on 4 islands in northern Vanuatu, in order toprovide information on the incursion of the little fire ant into thearchipelago (Fig. 1): VanuaLava (331 sq. km. population over 1400). thelargest island in the Banks group; Mota Lava (35 sq. km) 12 kmnorth-east ofVanua Lava; Gaua almost the size ofVanua Lava (330 sq.km, population over 1300) and Espiritu Santo, the largest island ofVanuatu (4010 sq. km, population over 23 000). Santo appears as acenter of trade and exchange for the northem islands. The risk of anarrivaI of W. auropunctata from Vanua Lava is high and if Santo isinvaded, the risk to dispatch the pest to all Vanuatu will be very high.The traditional custom exchanges of vegetal products (coconut trees.yams. taro, banana bunches...), which is a central process in theMelanesian social life, increase the risk of a rapid invasion of otherislands in Vanuatu as well as other Pacifie countries.
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1660 E
Sociobiology Vol. 40, No. 3, 2002
1680 1700 E
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~b Torres Islands..Il
PACIFICOCEA N 14° S
EspirituSanto
" ~MaewoAoba
· " 0uganv>!1 !::l,d Ao c::3 \) Pentecost
~ GAmbrymMaJekulaW (J <w
EP~ 0 Shepherd Islands<? '.
16°-
CORAL
SEA 18°-
ir~ Erromango
,Anlwa
Tanna0J G Futuna
0 50 100 150 200km
AnatomC)20' S-
Fig. 1. Situation map of Vanuatu archipelago.
•Jourdan, H. et al. - Little Fire Ant Spreads into Vanuatu
MATERlALS AND METHODS
487
Detection of the invader.A standard baiting method was used, instead of nonselective pitfall
traps, which need a much longer trapping period to detect \ittle fire antswhen their populations are low (Le Breton 1999). As bait, we usedcommercial Soya oil dropped on cotton dental rolls (L 35 mm x diam. 8mm), according to Way et al. (1998).
Vegetal oil was chosen because it is more attractive than sugar to W.auropunctata (Spencer 1941, Williams & Whelan 1992, Delsinne et al.2001). The baiting time varied from 25 minutes to 2 hours. The baitswere thus picked in the field and placed in closed plastic tubes. The antswere later identified to species and morphospecies under a stereomicroscope. Six to 20 baits were laid in each station. Visual searchcompleted the baiting.
List of surveyed localities.Espiritu Santo islandDept. of Agriculture Livestock and Forest Head Office, Harbor
seaside, Mosina village, Mosina taro field, Sola wharf area, Solabungalow, Village at Ngousourasal (airport vicinity).
Mota Lava islandMota Lava airfield, Nerenigmen village, Nerenigmen taro fields and
gardens, Valua village and gardens, Rd island bungalow.Gaua islandGaua Training Center, Losalava School, Santa Maria Schoo1.
RESULTS
During the course of the survey, 18 ant species (including W.auropunctata) have been observed or sampled (Table 1). This lowrichness can be explained by the places we searched, as we focussed onhuman settlements where the invader had the best chance to becomeestablished. This inventory bias toward human habitat also explainsthe high frequency of exotic ants.
Espiritu SantoEleven species have been recorded (Table 1). No W. auropunctatawere
detected, although we focussed on the collections and nursery plantscoming from Vanua Lava in Chapuis and Saraoutou nursery stations.Pheidole spp. appear the dominant ants on this island. Large populations of Pheidole megacephala have been detected in Luganville area(airport, harbor and in most urban areas). This species appearsrestricted to human vicinity (no population were recorded in bush or innursery stations). Paratrechina longicomis, an another tramp species,was also recorded in human vicinity. In sorne visited places. peoplecomplained about ant stings but these could be attributed toCrematogaster sp.
Vanua LavaVanua Lava is the place where we observed the lowest ant richness,
only six species have been recorded (Table 1). The two main villages,Sola and Mosina are heavily infested. Little fire ant thrives everywhere,under stones as well as in tree roots, in crevices ofconcrete basementsas well as in thatch roofs. In these villages, everybody is familiar withthe ant: W. auropunctata enters easily in many houses, if not all, anddense lines of foragers can be observed along every walls. To sorneextent, W. auropunctata coexists with Anoplolepis gracilipes in villageareas, but little fire ant workers are always dominant on baits and kills
•Jourdan, H. et al. - Little Fire Ant Spreads into Vanuatu 489
any A. gracilipes worker met in the foraged area. In Mosina, the sea sidearea seems not so heavily infested as in Sola. In both areas, W.auropunctata thrives in several taro fields, Httle fire ant nests in theleaves around the collar and people planting taro favor its dispersal. Theyellowing of taro leaves reported near Mosina is related to highpopulation of the taro leafhopper Tarophagus proserpina. along withinfestations of tetranychid mites. The ant probably benefits from theleafhopper honeydew. The survey did not allow to assess the contribution ofW. auropunctata to the T. proserpinainfestation orto evaluate thedamage to the yield. but people complained only for the stings. W.auropunctata has also invaded the bush and parts of the forest on 200to 300 m, on each side of the road. It does not seem to extend past to2 or 3 km from Sola towards the airfield and it is not continuous. A smallspot, just by the airfield, is also heavily infested (taro fields and villagearea) . A tiny stream separates the airfield from this area and seems toprevent further spread: the invader was not detected in the airportbuilding, on the airfield and in the surrounding bush and forest. Wewere also informed of a spot invaded in Vitimboso. 10 km west ofMosina. We estimatethe infested surfaceto up to 1000 ha. Le. up to 3%of the whole surface ofVanua Lava. One can also notice the absence ofP. megacephala on Vanua Lava.
Mota LavaNine species have been recorded. including large populations of P.
megacephala. as well as A. gracilipes. especially in human neighborhood (Table 1). No W. auropunctataweredetected ininspected fields andvillages. Stings in the airport area and in the village of Valua can beattributed to Crematogaster sp. But this island is under the invasivepressure through daily traffic by small boats with Vanua Lava. Ourfellows of Vanuatu Quarantine & Inspection Service (VQIS) evenstopped a man bringing back infested taros from Vanua Lava that heintended to plant on Mota Lava. The custom chiefs in Nerenigmen andValua were informed about the problem and on the interest for peopleto inspect and eventually destroy all vegetative material brought ontheir island from Vanua Lava or from Mota.
GauaAnt stings or bites reported before the survey led to the idea that little
fire ant had been introduced on the island. We sampled 9 ant speciesbut did not capture any W. auropunctata or P. megacephala (Table 1).The most common ants in the samples are Paratrechina longicomis andA. gracilipes. The stings or bites reported could be attributed toCrematogaster ants. The invasive pressure seems lower than on Mota
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Lava as the air and sea traffic with Vanua Lava and Santo are not soimportant as that between Vanua Lava and Mota. Mota Lava or Santo.
DISCUSSION AND RECOMMENDATIONS
To date; there is no evidence of Wasmannia auropunctata invasion onMota Lava. Gaua and Espiritu Santo, onlyVanua Lava is infested. Mota.a nearby island we did notvisit, also appears to be invaded. with at least250 ha infested (Tumukon 1999). The total affected area on these twoislands exceeded 1200 ha. But the invasive pressure on other islandsof the Banks group and on Espiritu Santo is high. especially on MotaLava. which is frequentlyvisited by people from Vanua Lava and Mota.
Impact of the invasion: what can be predicted.This invasion could have major implications for agriculture. economy
and welfare of the people in Vanuatu.W. auropunctata is a significant agricultural pest. Its painful sting
hinders agricultural work: it was reported as the prevalent cause for thefalling down of the coffee gathering in New Caledonia (Deloumeau1995). Through a large range mutualism with phytophageous insects,it favors the development of plant pests. among which are severalplagues for agriculture (Table 2). A generally low technicallevel in localgrowers allows uncontrolled insect pest outbreaks. as was witnessed onVanua Lava for the taro plant hopper, Tarophagus proserpina. The antis also a major plague of the natural environment: in the Galapâgos, ithas shown negative impacts on native invertebrates (Silberglied 1972;Clarketal. 1982; Lubin 1984); in New Caledonia. the little fire ant altersthe structure of the native arthropod and vertebrate communities(Jourdan 1997b, 1999; Jourdan & Chazeau 1999; Jourdan et al. 2001).
Negative effects are more often recorded. though statements on abeneficial action of W. auropunctata against several pests have beenpublished (Table 3). Although Souza et al. (1998) stated that w.auropunctata could not keep phytophageous insects under control incocoa plantations in Brazil because of large seasonal populationvariations. This lack of efficiency could in fact be predicted with anyopportunist or broad spectrum predator.
As reported in our survey as weIl as in other countries (Spencer 1941;Delabie et al. 1995; Klotz et al. 1995), W. auropunctata invades houseseasily. where it can establish nests in roofs and wall crevices. In houses,it seems more attracted by fat than sugar (Spencer 1941; Femald 1947;Smith 1965). Its irritating sting raises concem for public comfort andhealth. Skin itching may last several days and a few people may displayallergic reactions. due to repetitive stings (Spencer 1941, Cochereauunpublished). Though it is not a vector of disease, W. auropunctata
Table 2. List of insects for which mutualism with W. auropunctata has been recorded.
Cammon Names Host Plants Countries ReferencesHomoptera •Aleyrodidae Aleurothrixus floccosus Wooly whitefly Citrus spp. USA (Florida) Spencer (1941)
Dialeurodes citritolii Cloudy-winged whitefly Citrus spp. USA (Florida) Spencer (1941)
Heteropsylla cubana Leucaena psyllid (Leucena leucocephala) West Indies area Pollard & Persad (1991) :::lc
Different phytophageous insects Gocoa (T. cacao) Brazil Maker & Delabie (1993) D>ë
Different phytophageous insects Maize (Zea mays), Gabon Wetterer et al. (1999)Gocoa (T. cacao)
Protection given b y W. auropunctata to certain Pseudococcus should result in a positive action against black pod disease: bacteria associatedwith these Mealybugs seem to be an antagonist of the pathogen agent.
~
CDW
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couId be a potential vector ofpathogens in hospitals (Fowler et al. 1993;Bueno & Fowler 1994). It is also responsive to veterinary problems.Blindness (keratitis) ofdomestic dogs or cats is fairly common in heavilyinfested areas and attacks on young chickens have been reported inNew Caledonia, the Solomon Islands and Gabon (Jourdan 1999;Wetterer et al. 1999). Such clinical events (keratitis) couId be similiarto those described on calves with Solenopsis invicta stings in Southwestern United States (Joyce 1983 in Jemal & Hugh Jones 1993).Exclusion of caUle grazing and breeding from heavily infested bush inNew Caledonia has also been reported (Cochereau unpublished). Thisexclusion process may be similar to the one described on white taileddeer breeding in Texas with the spread ofred fire ants (Allen et al. 1997).Further veterinary inspections are necessary to assess the magnitudeof these problems.
Eradication: can it be achieved?The invasions of the Galapâgos and NewCaledonia provide informa
tion on which results can be expected from different control measures.On Santa Fe Island (Galapâgos) an intensive control program aimed toeradication of the invader was conducted in mid 70's, with the removalof rocks and herbs, the burning of the area and the application ofpyrethrin and DDT. These drastic attempts did not succeed, and did notprevent the ant from being detected again 6 years later (Abedrabbo1994). Another attempt was conducted on a small scale, using thecommercial bait Arndro™ (Hydramethylnon) on a small (2 ha) andlightly infested area with an apparent success (Abedrabbo 1994).Though these results are encouraging, experiments conducted so far inthe more rainy conditions of New Caledonia do not allow such optimism(Chazeau etal. 2000). In New Caledonia burning has been discouraged,but attempts to control the ant by spraying pesticides (Diazinon™) havebeen conducted by the agriculture staff, leading to the conclusion thatthe ants were present again soon after in the treated areas (Chazeau etal. 2000).
In Vanuatu, the total invaded area reaches up to 10 sq. km. Assumingthat Arndro™ is to be applied between 2.0 and 2.5 kg/ha (Petty &Manicom 1995; Chazeau et al. 2000), up to 2500 kg would be used forone single treatment of infested areas. 1'0 increase efficiency of eradication program, it will require applying several more treatments (2 oreven more), that will require use of several tons ofArndro™, even ifbaitapplications are focused on drier periods ofthe year. As the infested areaincludes important parts of dense bush and steep slopes also, efficientbait utilization will also be impaired (a systematic baiting grid could notbe applied, as used in the Galapâgos (Abedrabbo 1994)).
•
Jourdan, H. et al. - Little Fire Ant Spreads into Vanuatu 495
As pointed out by Myers et al. (2000), six factors contribute tosuccessful eradication of an introduced species: 1) resources must besufficient to fund the program to its conclusion; 2) the lines ofauthoritymust be clear and must allow an individual or agency to take allnecessary actions; 3) the biology of the target organism must make itsusceptible to control procedures (dispersal ability, reproductive biology... ); 4) reinvasion must be prevented; 5) the invader should bedetectable at relatively low densities, to have early detection before itbecomes widespread; 6) restoration or management of the treatedcommunity may often be required after process of eradicating (becauseof the impact on nontargeted species).
Most of these requirements are not achieved in Vanuatu, no eradication attempt can thus be recommended, as it will involve high costs forhypothetical results. The risk offurther reinvasions appear high. Otherentrypoints than those so faridentified mightalso existin the northemislands ofVanuatu : people move frequently with small boats, transporting plants, from island to island. Slowing the rate of spread might bemore feasible and cost effective.
Limited control measures.Controlling this ant is a hard task. In Vanuatu, most people do not
use insecticides for economical reasons (high costs). They bum theants, pour hot water on them, pour oil or petrol around homes.sometime bait them with food and either bum the gathering ants or poorhot water on them. But these measures do not provide efficient controland the ants soon re-invade the treated area. Most effective control canbe achieved by the use of poison baits, instead of contact insecticides.because it is brought back to the nest and kill brood and queens.
In a control program, one must distinguish between public healthand comfort, agriculture needs and natural environment concerns. Toprovide reliefto people in infested areas, control restricted to homes andin their vicinity could be achieved by the adequate use of insecticides.The use of a commercial bait like ArndroT
" seems appropriate to thisobjective (Williams & Whelan 1992; Petty & Manicom 1995). Altematively, spraying the soil, walls and roofs with pyrethrins could providean appreciated relief but will not provide effective control. Baits andsprays must never be used at the same time. When no insecticide isavailable, simple tricks can provide relief to sleepers, like isolating thefeet of the beds with tin cans filled with mineraI oil, or using a sheet asa tent over the beds to prevent the ants from falling from the roof (asobserved in many houses in infested areas). The same chemical controltechniques could be applied to gardens and fruit trees, but the high costofpoison baits will probably not allow large field use. Also, Arndro™ baits
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could be inefficient under rainy conditions (Chazeau et al. 2000).Spraying of contact insecticides to kill the ant workers only whennecessary (before harvesting the crops...) could also be done. A cheaperalternative for trees is to use coconut oil and insecticide rings (DiazinonT
")
around the trunks, to prevent little fire ants' access to branches andfruits (Cochereau & Potiaroa 1994). Not much seems feasible in theinvaded natural areas, so the only recommendation is to delay theinvasion of free areas by a serious prevention policy.
As pointed out for Solenopsis invi.cta and Linepithema humile in theUSA (Porter et al. 1997; Holway & Suarez 1999), transplantation out ofnative areas should result in a competitive advantage for the invader,because it escapes from its own parasites, predators and nativecompetitors. lt also maximizes its habitat exploitative capabilities. Butto date. no parasite or predator can be recommended for the biologicalcontrol of W. auropunctata. Competition with other ants. especiallyother tramp species. could help in the control of the little fire ant.Pheidole megacephalacan efficiently compete with W. auropunctataandprobably contributes to the containment by blocking entry points, asindicated by observations in Santo and Mota Lava. Delabie et al. (1995)have shown a negative association between W. auropunctata andP. megacephala in habitations in Brazil. Sorne observations in NewCaledonia indicate fierce competition between W. auropunctata and P.megacephalaat least in inhabited areas (Jourdan 1999). Analogies canbe found with the competitive replacementbetween P. megacephalaandL. humilein Madeira (StoIl1898). in Bermuda (Haskins & Haskins 1965,1988; Liberburg et al. 1975), or in Hawaii (Cole et al. 1992; Wettereret al. 1998). But one must remember that P. megacephala is also atramp ant, which favors coccids and is considered as a serious pest inthe wild areas ofHawaii and Northern Australia (Hoffmann et al. 1999;Vanderwoude et al. 2000).
Our survey is also a claim to achieve biodiversity assessment of theant fauna in Vanuatu. Such information will help in the search ofpotential competitors as weIl as assessing the range ofthreatened fauna(using ants as bioindicators of the threats). From literature. we recordonly 46 species (in 28 genera) from the whole archipelago. lt includes3 endemics but 2 subspecies. as weIl as 14 introduced species.including W. auropunctata (Table 4). Vanuatu ant taxonomic data arescattered and there is an inventory bias toward northern Vanuatu.especially Espiritu Santo and Malekula (39 species recorded from these2 islands). In turn. the ant fauna richness appears very low andunderestimated ifcompared with adjacentarchipelago: New Caledonia.with up to 160 species in 45 genera (Jourdan 1999) and the Solomon
Table 4. List of ant species recorded fram Vanuatu.
Synonyms Localities References Status
PonerinaeAmblyopone australis Erihson, 1842 Tanna Wilson (1958a) NAnochetus graeffei Mayr, 1870 Espiritu Santo Wilson (1959a) N?Hypoponera confinis (Roger), 1860 Panera confinis Malekula Wilson (1958b) I? c....
0Hypoponera pruinosa (Emery), 1900 Ponera pruinosa Espiritu Santo, Vanua Wilson (1958b) N c
a.Lava, Malekula Il>
Hypoponera punctatissima (Roger), 1859 First identified as Ponera Tanna Wilson (1958b),.:J
Leptogenys hebrideana Wilson, 1958 Espiritu Santo Wilson (1958a) EOdontomachus simillimus Smith F., 1858 Fi rst identified as Efate, Aore, Espiritu Emery (1914), Wilson N? r
aOdontomachus haematoda Santo, Mata Lava (1959a), this study CD
Pachycondyla stigma (Fabnicius), 1804 Trachymesopus stigma Espiritu Santo Wilson (1959b) N »Ponera c1avicomis Emery, 1900 Espiritu Santo, Malekula Wilson (1957) N 3-Ponera incerta (Wheeler WM), 1933 Ponera ratardorum Espiritu Santo Wilson (1957) N Ul
"0éD
DolichoderinaeIl>a.
Ochetel/us glaber (Mayr), 1862 Espiritu SantoCIl
Iridomyrmex glaber Emery (1914) N S'Tapinoma melanocephalum (Fabricius), 1793 Tapinoma melanocephalum Espiritu Santo, Tanna, Sanstchi (1928), Jourdan 1 ô
5'Tetramorium tonganum Mayr, 1870 Etate, Malekula Bolton (1977) N ôVollenhovia denticulata Emery, 1914 Espiritu Santo Wilson & Taylor (1967) N <
0>Vollenhovia oblonga (Smith, F.), 1860 Espiritu Santo Wilson & Taylor (1967) N ::::l
C
Wasmannia auropunctata (Roger), 1863 Vanua Lava, Mata This study 1 0>ë
1: Introdueed; N: Native E: Endemie
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Islands. with up to 180 speciesin 52 genera (Mann 1919. Wheeler 1935.Wilson & Taylor 1967, Taylor 1976, Bolton 1995) or Fiji with up to 110species in 35 genera (Mann 1921, Wheeler 1935. Wilson & Taylor 1967,Bolton 1995. Dlussky 1995). Nevertheless, we can notice affinities withthe Solomon's ant fauna (Turneria sp., Pristomyrmex sp., Myrmecinasp., Pachycondyla sp.) though Southern Vanuatu seems to have wideraffinities with the New Caledonian fauna, as shown by Wilson (l959c)and further emphasis with herpetofauna data from Tanna island (Bauer1999).
Containment measures.The biological and ecological characteristics ofW. auropunctatahave
implications for its containment. Given its low capacity of dispersion,the risk ofrapid natural spread is low: massive mating tlights have neverbeen observed and colonies extend through budding (Ulloa Chacon1990, Jourdan 1999). Spreading that way is always slow, probablymuch less than 500 m ayear (Meier 1994). The tinynests maybe foundin any modest shelter. most often in soil crevices, under pieces ofwoodor stones, or in liUer; they also can be found under bark or in epiphytes.But in W. auropunctata, a nest includes several queens with highfecundity (Ulloa Chacon 1990). These characteristics explain whyrapidspreading means human mediated dispersion. Despite this low intrinsic dispersion capacity, long term natural spreading may occur on sorneinfrequent occasions (flooding and heavy rainfalls). Groups ofW. auropunctatahave been seen floating on streams. This may result inthe colonization of new areas as witnessed in New Caledonia (Jourdan1999) and as known for several neotropical ants (Jaffé 1993). includingS. invicta(MorillI974) and L. humile (Barber 1916) spreadingin UnitedStates. Masses of W. auropunctata have been observed floating on thesea up to 1 km from the New Caledonian coast (Jourdan 1999). Nestson floating woods might allow the colonization of sorne islands asobserved for Pheidole sp. in Brazil (Wheeler 1916). Given the geographyof Vanuatu, the probability of such dispersion processes appear to below.
The transportation of nests by human activities must be avoided. Itis the only overseas dispersal way and also the only quick dispersalopportunity inside invaded islands. The invasion of Santo - and, ofcourse, of Efate - should be absolutely avoided. Their agriculturalactivities are associated with a trade node role, thatwill soon contributeto disperse the invader in other islands. The restoration (throughefficient quarantine measures) of isolation boundaries broken byhuman transport appears to be a realistic solution to prevent furtherspreading. Transportofsoil, timber, thatch, building material, bunches
Jourdan, H. et al. - Little Fire AnI Spreads into Vanuatu 501
offruits. furniture. etc. should be prohibited between infested areas andfree areas in the invaded islands. as weIl as around the Banks group andother islands. Ifsuch transports cannot be avoided. a rapid assessmentto confirm the absence of W. auropunctata in this material should beconducted prior to transport. as weIl as in the arrivaI area during thefollowing weeks. Quarantine decision to spray the planes coming [romthe Banks should also reduce new invasion. even if spraying could beinefficient against W. auropunctata brood.
Detection should be organized in order to allow a faster reaction tothe invasion in every entry points and to provide a better appraisal ofthe ant dispersal on invaded islands. A standard baiting techniqueusing soya oil baits (or other vegetal edible oil) couId be implemented bythe staff involved in the detection program. The concept ofentry pointsmust be extend to every island and a monthly survey of the stations.which may receive and dispatch plants. soils. litter ... from and to otherislands. should be promoted to efficiently detect low populations. Thenursery plantations and agricultural stations (plant collection anddispatching) in the archipelago should be involved and immediatelystart their own survey of transit areas. The 3 trading ships which calIto Santo and other islands (Maewo. Pentecost. Malekula) after callingto the Banks as weIl as the ship of the anglican Diocese of Melanesiawhich visits Vanuatu each year. calling from the Solomon. should beinspected; captains and crew should be seriously informed on thesituation and on their responsibility in the quarantine process.
Prevention through early detection and general awareness must bepromoted. Traditional chiefs and people of the villages where the piersand airfields are located should be specially informed and deeplyinvolved in the quarantine process. To get full cooperation fromVanuatu people. who frequently move inside and between islands. theyshould be made aware of the ant problems as well as to be informed onthe reasons why they are highly concerned. It will require an intenseand sustained campaign of information and awareness. especially onhow small a nest can be and how easily it can be transported. Frequentradio advice could be used. as was efficiently done in the country for theAspidiotus destructor control campaign in the sixties and seventies(Cochereau 1969). Mind-striking leaflets illustrated with short comics.telling truthful stories of transportation (on taro plant. on bananabunches), seem appropriate for scholars as weIl as for general use.These printed stories should be widely distributed in the archipelagoand will be necessary to inform the Banks villages which radiobroadcasting cannot reach. Every structure interested in communityprograms should be associated to the information campaign and
502 Sociobiology Vol. 40, No. 3, 2002
containment program, especiaUy involving the official staff, the media,the schools and the churches.
W. auropunctata is a real threat to aU Pacific countries. The geographic, social, economic and technical realities of many neighboringcountries are similar to Vanuatu. They thus should take lessons fromthis experience to prevent the spread of this exotic ant and to reactbefore it becomes strongly established.
ACKNOWLEDGEMENTS
On a request of Vanuatu authorities, the Pacific Community PlantProtection Service funded this inspection in northern Vanuatu. Theproject was warmly supported by Dr. Jimmie Rogers and officiaIs ofSuva-based Agriculture staff. Thanks to Tim Tumukon, Maurice Horryand Selei Bob (VQIS staff) and to Dr. Guenther Rapp (SPC) for theirfriendlyand efficient help during field work ; to the council of the TorbaProvince for kind assistance and car facilities; to the staff at theAnglican Church in Santo and Sola; to the Directors and the staff ofChapuis Station, Saraoutou Station and the Kava farm in Fanafo for fullcooperation. Thanks to the chiefs and people of the villages we visitedin Santo, Vanua Lava, Mota Lava and Gaua for theirwelcome and kindassistance.
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Jourdan Hervé, Bonnet de Larbogne Lydia, Chazeau Jean.
(2002)
The recent introduction of the neotropical tramp ant
Wasmannia auropunctata (Hymenoptera : Formicidae) into
