483 The Recent Introduction of the Neotropical Tramp Ant Wasmannia auropunctata (Hymenoptera: Formicidae) Into 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 , , 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 capacityis low. An eradication program does not appear to be a realistic goal. given the actual extent ofthe invasion. Slowing the spread of the exotic antappears 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] 484 Sociobiology Vol. 40, No. 3, 2002

Costa Rica) (Fabres & Brown 1978, Longino & Nadkami 1990). It is mainlya terricolous species, nesting in litter (between dead leaves or in rotton wood) either in soil or at the base of trees (especially in the dry season). 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 diagnosis comprises an antennae 11-segmented. with a 3-segmented club. Antennal scrobes are present. bounded below by a weak longitudinal carinarunningabove the eyes. Anterodorsal angles ofthepronotumare acute. the pronotum is strongly marginate anteriorly. Promesonotal suture is absent. metanotal grove is weakly impressed. Propodeum is bispinose. metapleuallobes are present. Wasmannia auropunctata: an invasive ant spreading worldwide. During pastdecades, human activities have spread this tiny stinging ant, so its distribution is nearly pantropical. Despite the seven subspe­ cies that are currently recognized for W. auropunctata (Bolton 1995), in most reported invasions. the subspecific name is not specified. Accord­ ing to Kempfs catalogue (1972) and Wetterer & Porter (comm. pers.), it seems likelythatmostorall invasive are W. auropunctataauropunctata. Littlefire ants are nowrecorded from Cocos island (ForeI1902; Hogue & Miller 1981). Florida (Wheeler 1929). Bermuda (Hilbum et al. 1990), Bahamas (Wetterer & Porter comm.pers.), Cameroon (Bruneau de Miré1969), Gabon (Santschi 1915; Wetterer et al. 1999), Galâpagos (Silberglied 1972; Pezzati etal. 1998), Solomon (on Guadalcanal island as well as on Sola and Vulelua. but other islands may be affected) (MacfarlaneinWaterhouse& Norris 1989;Wetterer 1997), New Caledonia and 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), and Vanuatu (Tumukon 1999; Rapp 1999). But. it is still spreading in the Tropical Pacifie: according to Nishida & Evenhuis (2000), it may have reached Fiji shores. The little fire ant would also present on the coast ofSumatra island (Bruneau de Miré pers. comm.), in the coastal region ofPointe Noire inPopular Republic ofCongo (Veysseyre pers. comm.) as well as in Democratie Republic ofCongo (ex Zaire), according to Fowler etal. (1994). W. auropunctatawas also recorded in Califomia (Nickerson 1983), but its permanent establishment there appears doubtful (Ward pers. comm.). Several populationshave also beenrecorded from tropical greenhouses in different temperate areas (Donisthorpe 1927; Ayre 1977; 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 ofits painful sting, W. auropunctata is a well known pest in every place where outbreaks occur. So a wide array of local names characterize 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, "fourmi electrique" in New Caledonia or "tsangonawenda" in Gabon (Smith 1936; Bruneau de Miré 1969; Delabie 1989; Ulloa Chacon 1990; Jaffe & Lattke 1994; Jourdan 1997b; Wetterer et al. 1999). The species is a representative 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 after perturbation) which facilitated its spread through human mediated dispersal. Origins of invasion into Vanuatu archipelago. Wasmannia auropunctata was first detected in June 1998, in the Banksisland group, North ofVanuatu (Fig. 1). VanuaLavawasreported as the first invaded island. According to local informers, the ant had probably been introduced in 1994-1995 on building materials. im­ ported by the Melanesia anglican diocese ship, calling from Honiaravia Sola, in the Solomon. In Mid 1999, reports assessed its presence on Vanua Lava and Mota and mentioned unconfirmed reports of its presence on (Tumukon 1999; Rapp 1999). Our survey focussed on 4 islands in northern Vanuatu, in order to provide information on the incursion of the little fire ant into the archipelago (Fig. 1): VanuaLava (331 sq. km. population over 1400). the largest island in the Banks group; (35 sq. km) 12 km north-east ofVanua Lava; Gaua almost the size ofVanua Lava (330 sq. km, population over 1300) and , the largest island of Vanuatu (4010 sq. km, population over 23 000). Santo appears as a center of trade and exchange for the northem islands. The risk of an arrivaI of W. auropunctata from Vanua Lava is high and if Santo is invaded, 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 the Melanesian social life, increase the risk of a rapid invasion of other islands in Vanuatu as well as other Pacifie countries. •

486 Sociobiology Vol. 40, No. 3, 2002

1660 E 1680 170 0 E ~b

..Il PACIFIC OCEA N 14° S

" ~ Aoba Espiritu Santo uganv>!1·"!::l,d 0 A o c::3 \)Pentecost 16°- ~ GAmbrym MaJekulaW (J

CORAL SEA 18°-

~

,Anlwa

ir Tanna0J G Futuna 0 50 100 150 200km

20' S- AnatomC)

Fig. 1. Situation map of Vanuatu archipelago. •

Jourdan, H. et al. - Little Fire Ant Spreads into Vanuatu 487

MATERlALS AND METHODS Detection of the invader. A standard baiting method was used, instead of nonselective pitfall traps, which need a much longer trappingperiod to detect \ittle fire ants when their populations are low (Le Breton 1999). As bait, we used commercial Soya oil dropped on cotton dental rolls (L 35 mm x diam. 8 mm), 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 baits were thus picked in the field and placed in closed plastictubes. The ants were later identified to species and morphospecies under a stereo microscope. Six to 20 baits were laid in each station. Visual search completed the baiting. List of surveyed localities. Espiritu Santo island Dept. of Agriculture Livestock and Forest Head Office, Harbor Quarantine office, Harbor scale area, Harbor copra sheds (all), Harbor passengers shed, BP Wharf, Milcoffea Warf, Dinvandan Wharf, Mango village, Mango station, Santo dump (forbidden material buming place), Beachfront Motel, Hospital, Bishop garden (Sarakata area), Chapuis Station (Banks isl. Taro Collection), CARFV Saraoutou Station, (Banks is1. Taro, Kava and Coconut Collections). Vanua Lava island Mota airfield, Mosina copra drier, Mosina copra shed, Mosina seaside, Mosina village, Mosina taro field, Sola wharf area, Sola bungalow, Village at Ngousourasal (airport vicinity). Mota Lava island Mota Lava airfield, Nerenigmen village, Nerenigmen taro fields and gardens, Valua village and gardens, Rd island bungalow. Gaua island Gaua 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 low richness can be explained by the places we searched, as we focussed on human settlements where the invader had the best chance to become established. This inventory bias toward human habitat also explains the high frequency of exotic ants. •

488 Sociobiology Vol. 40, No. 3, 2002

Table 1. List of collected ants.

Espiritu Santo Vanua Lava Mota Lava Gaua

Anoplolepis gracilipes + + + Camponotus sp. + + Crematogaster sp. + + + Monomorium sp.1 + Monomorium sp.2 + Monomorium sp.3 + Myrmecina sp. + + + Odontomachus simillimus + + Partrechina longicornis + + + + Pheidole megacephala + + Pheidole sexspinosa + Pheidole umbonata + + + Pheidole sp.1 + + + Pheidole sp.2 + Tetramorium sp.1 + + Tetramorium sp.2 + Tetramorium sp.3 + Wasmannia auropunctata +

Espiritu Santo Eleven species havebeen recorded (Table 1). No W. auropunctatawere detected, although we focussed on the collections and nursery plants coming from Vanua Lava in Chapuis and Saraoutou nursery stations. Pheidole spp. appear the dominant ants on this island. Large popula­ tions of Pheidole megacephala have been detected in Luganville area (airport, harbor and in most urban areas). This species appears restricted to human vicinity (no population were recorded in bush or in nursery stations). Paratrechina longicomis, an another tramp species, was also recorded in human vicinity. In sorne visited places. people complained about ant stings but these could be attributed to Crematogaster sp. Vanua Lava Vanua 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 basements as well as in thatch roofs. In these villages, everybody is familiar with the ant: W. auropunctata enters easily in many houses, if not all, and dense lines of foragers can be observed along every walls. To sorne extent, W. auropunctata coexists with Anoplolepis gracilipes in village areas, 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 side area seems not so heavily infested as in Sola. In both areas, W. auropunctata thrives in several taro fields, Httle fire ant nests in the leaves around the collarand people plantingtaro favor itsdispersal. The yellowing of taro leaves reported near Mosina is related to high population of the taro leafhopper Tarophagus proserpina. along with infestations of tetranychid mites. The ant probably benefits from the leafhopper honeydew. The survey did not allow to assess the contribu­ tion ofW. auropunctatato the T. proserpinainfestationortoevaluate the damage to the yield. but people complained only for the stings. W. auropunctata has also invaded the bush and parts ofthe forest on 200 to 300 m, on each side of the road. It does not seem to extend past to 2 or3 km from Solatowards the airfield and itis notcontinuous. Asmall spot, justby the airfield, is also heavily infested (taro fields and village area) .A tiny stream separates the airfield from this area and seems to prevent further spread: the invader was not detected in the airport building, on the airfield and in the surrounding bush and forest. We were also informed of a spot invaded in Vitimboso. 10 km west of Mosina. We estimatethe infested surfaceto up to 1000 ha. Le. up to 3% ofthe whole surface ofVanua Lava. One can also notice the absence of P. megacephala on Vanua Lava. Mota Lava Nine species have been recorded. including large populations of P. megacephala. as well as A. gracilipes. especially in human neighbor­ hood (Table 1). No W. auropunctataweredetected ininspected fields and villages. Stings in the airport area and in the village of Valua can be attributed to Crematogaster sp. But this island is under the invasive pressure through daily traffic by small boats with Vanua Lava. Our fellows of Vanuatu Quarantine & Inspection Service (VQIS) even stopped a man bringing back infested taros from Vanua Lava that he intended to plant on Mota Lava. The custom chiefs in Nerenigmen and Valua were informed about the problem and on the interest for people to inspect and eventually destroy all vegetative material brought on their island from Vanua Lava or from Mota. Gaua Antstings or bites reported before the survey led to the idea that little fire ant had been introduced on the island. We sampled 9 ant species but did not capture any W. auropunctata or P. megacephala (Table 1). The mostcommon ants in the samplesare Paratrechina longicomis and A. gracilipes. The stings or bites reported could be attributed to Crematogaster ants. The invasive pressure seems lower than on Mota •

490 Sociobiology Vol. 40, No. 3, 2002

Lava as the air and sea traffic with Vanua Lava and Santo are not so important as that between Vanua Lava and Mota. Mota Lava or Santo. DISCUSSION AND RECOMMENDATIONS To date; there is no evidence ofWasmannia auropunctatainvasionon Mota Lava. Gauaand EspirituSanto, onlyVanuaLava isinfested. Mota. a nearbyisland we did notvisit, also appears to beinvaded. with at least 250 ha infested (Tumukon 1999). The total affected area on these two islands exceeded 1200 ha. But the invasive pressure on other islands of the Banks group and on Espiritu Santo is high. especially on Mota Lava. which is frequentlyvisited by people from Vanua Lava and Mota. Impact of the invasion: what can be predicted. This invasion could havemajor implicationsfor agriculture. economy and welfare of the people in Vanuatu. W. auropunctata is a significant agricultural pest. Its painful sting hinders agriculturalwork: itwas reported as the prevalentcause for the falling down of the coffee gathering in New Caledonia (Deloumeau 1995). Through a large range mutualism with phytophageous insects, it favors the development of plant pests. among which are several plagues for agriculture (Table 2). A generally low technicallevel in local growers allows uncontrolled insect pestoutbreaks. aswaswitnessed on Vanua Lava for the taro plant hopper, Tarophagus proserpina. The ant is also a major plague of the natural environment: in the Galapâgos, it has shown negative impacts on native invertebrates (Silberglied 1972; Clarketal. 1982; Lubin 1984); in New Caledonia. the little fire ant alters the structure of the native arthropod and vertebrate communities (Jourdan 1997b, 1999; Jourdan & Chazeau 1999; Jourdan etal. 2001). Negative effects are more often recorded. though statements on a beneficial action of W. auropunctata against several pests have been published (Table 3). Although Souza et al. (1998) stated that w. auropunctata could not keep phytophageous insects under control in cocoa plantations in Brazil because of large seasonal population variations. This lack of efficiency could in fact be predicted with any opportunist or broad spectrum predator. As reported inour surveyasweIl as inothercountries (Spencer 1941; Delabie etal. 1995; Klotz et al. 1995), W. auropunctata invades houses easily. where it can establish nests in roofs and wall crevices. In houses, itseems more attracted by fat than sugar (Spencer 1941; Femald 1947; Smith 1965). Its irritating sting raises concem for public comfort and health. Skin itchingmay last several days and a few people may display allergic reactions. due to repetitive stings (Spencer 1941, Cochereau unpublished). Though it is not a vector of disease, W. auropunctata Table 2. List of insects for which mutualism with W. auropunctata has been recorded.

Cam mon Names Host Plants Countries References Homoptera Aleyrodidae Aleurothrixus floccosus Wooly whitefly Citrus spp. USA (Florida) Spencer (1941) • Dialeurodes citritolii Cloudy-winged whitefly Citrus spp. USA (Florida) Spencer (1941)

Aphididae Aphis gossypii Cotton aphid Cotton Dominican Menozzi & Russo (Gossypium sp.) Republic (1931) Citrus spp. USA (Florida) Spencer (1941) c... 0 Aphis spiraecola Green citrus aphid Citrus spp. USA (Florida) Spencer (1941 ) c a. Toxoptera aurentii Black citrus aphid Citrus spp. USA(Florida) Spencer(1941), Ql Nielsson et al. .::J (1971) ::r: Mango trees New Caledonia Jourdan ~ (Mangitera indica) (Unpublished) :-Il:> Toxptera citricida Tropical citrus aphid Citrus spp. Puerto Rico Michaud (1988) r- a Coccidae Cerastoplastes Mexican wax scale & Mango trees (M. indica) , ëD ceriterus & C. rubens Pink-wax scale Eugenia lateriflorum, "Tl ~. Paperback trees(Melaleuca New Caledonia Cochereau & l> quinquenervia), Potiaroa (1994) ;:;. Semecarpus atra, CIl "0 Caribbean pines (Pinus CD Ql caraibeae),Citrus spp. 0. C. elongatus Citrus spp. U'I New Caledonia Cochereau & S' Potiaroa (1994) ô C. f10ridensis Florida wax scale Citrus spp. USA (Florida) Spencer (1941 ) Ql< Coccus viridis Soft green scale Coffea spp. ::J Puerto Rico Smith (1942) c Citrus spp., Frangipani New Caledonia Cochereau & Ql ë (Plumeria alba), Coffea spp. Potiaroa (1994) Pulvinaria psidii & Green shield scale Frangipani (P. alba), Coffea spp., Guava trees New Caledonia Cochereau & Pulvinaria sp. (Psidium guajava) Potiaroa (1994) Saissetia hemisphaerica Hemispherical scaJe Coffea spp. Puerto Rico Smith (1936) Coffea spp. New Caledonia Cochereau & Potiaroa (1994) ~ CD~ Table 2 (cont).List of insects for which mutualism with W. auropunctata has been recorded. (0 1\)""" Common Names Host Plants Countries References

Goccidae (cont.) Saissetia nigra Nigra scale Citrus spp., Frangipani , New Caledonia Gochereau & (P. alba) Coffea spp. Potiaroa (1994) Saissetia sp. Gocoa (Theobroma cacao) Cameroon Bruneau de Miré (1969) Toumeyella Iignumvitae Guaiacum sanctum USA (Florida) Williams (1993) Margarodidae Eurhizoccus brasiliensis Vitis sp. Brazil Soria et al. (1996) Icerya purchasi Cottony cushion scale Citrus spp. USA (Florida) Spencer (1941)

(j) Pseudococcidae Pseudococcus sp. Mealybugs Inga vera in coffee Dominican Menozzi & 0 () plantations Replubic Russo (1931) o' cr- Pseudococcus spp. Mealybugs Gocoa (T. cacao) Cameroon Muller et al. (1970) o' 0 Planococcus citri Citrus mealybug Gocoa (T. cacao) Brazil Delabie et al. ce (1994) '< < Fulgoroidea Tarophagus proserpina Taro leafhopper Taro (Colocasia esculenta, Wallis & Futuna Gutierrez (1981) Q. Alocasia macrorrhiza) Vanuatu This survey _0""" z !J Psylloidea Mesohomotoma sp. Gocoa (T. cocao) Cameroon Bruneau de Miré _w (1969) 1\) 0 Phacopteron sp. Okoumé (Aucoumea Cameroon Grimaldi (in 0 klaineana) Bruneau de Miré 1\) 1969) unknown species Acacia spirorbis New Caledonia Ghazeau et al. (1977)

Lepidoptera Riodinidae Eurybia e/Vina Calathea ovandensis Mexico Horvitz & Schemske (1984), Horvitz et al. (1987) Thisbe irenea Croton billbergianus Panama De Vries (1991) • Table 3. List of biological control activity recorded for W. auropunctata. • Common Names Host plants Localities References

Homoptera: some scales insects Coffee (Coffea sp.) Dominican Republic Menozzi et Russo (1931)

c- Fungi: Pythiaceae: o c Phytophtora palmivora Black pod disease Gocoa Gameroon Muller et al. Ci (Theobroma cacao) D> (1970 r _:::l ;:c Heteroptera: Miridae: m. Sahlbergella singularis Gocoa bug Gocoa (T. cacao) Gameroon Bruneau de Mire D> (1969) :- Amblypelta cocophaga Goconut nutfall bug Goconut trees Solomon Islands Macfarlane (1985 in r (Cocos nuci era) (Guadalcanal) Waterhouse & Norris Ë! 1989) CD ""T1

~~r Coleoptera: Cucurlionidae: » Diaprepes abbreviatus Weevil Citrus spp. Guadeloupe/Martinique Jaffe et al. (1990) 2- rn (French West Indies) "0 Diaprepes abbreviatus Weevil Sugarcane Florida & West Indies Sirjusingh et al. ro D> c- (Saccharum officinarum) area (1992) C/) Cosmopolites sordidus Banana weevils Bananas (Musa spp.) Venezuela Goitia & Gerda (1998) S· ô < Homoptera : Psyllidae: D> :::l Heteropsylla cubana Leucaena psyllid (Leucena leucocephala) West Indies area Pollard & Persad (1991) c D> Different phytophageous insects Gocoa (T. cacao) Brazil Maker & Delabie (1993) 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 associated with these Mealybugs seem to be an antagonist of the pathogen agent.

~ CD W •

494 Sociobiology Vol. 40, No. 3, 2002 couId be a potentialvector ofpathogens in hospitals (Fowler etal. 1993; Bueno & Fowler 1994). It is also responsive to veterinary problems. Blindness (keratitis) ofdomestic dogs orcats isfairly common in heavily infested areas and attacks on young chickens have been reported in New Caledonia, the Solomon Islands and Gabon (Jourdan 1999; Wetterer et al. 1999). Such clinical events (keratitis) couId be similiar to those described on calves with Solenopsis invicta stings in South­ western United States (Joyce 1983 in Jemal & Hugh Jones 1993). Exclusion of caUle grazing and breeding from heavily infested bush in New Caledonia has also been reported (Cochereau unpublished). This exclusion process may be similar to the one described on white tailed deerbreedinginTexaswith the spread ofred fire ants (Allen etal. 1997). Further veterinary inspections are necessary to assess the magnitude of these problems. Eradication: can it be achieved? The invasions ofthe 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 to eradication ofthe invader was conducted in mid 70's, with the removal of rocks and herbs, the burning of the area and the application of pyrethrinand DDT. These drastic attempts did notsucceed, and did not prevent the ant from being detected again 6 years later (Abedrabbo 1994). Another attempt was conducted on a small scale, using the commercial bait Arndro™ (Hydramethylnon) on a small (2 ha) and lightly infested area with an apparent success (Abedrabbo 1994). Though these results are encouraging, experiments conducted sofar in the more rainy conditions ofNew Caledoniado notallow such optimism (Chazeau etal. 2000). In New Caledoniaburninghas been discouraged, butattempts to control the antbysprayingpesticides (Diazinon™) have been conducted by the agriculture staff, leading to the conclusion that the ants were present again soon after in the treated areas (Chazeau et al. 2000). InVanuatu, the total invaded area reaches up to 10 sq. km. Assuming that 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 for one single treatment of infested areas. 1'0 increase efficiency of eradi­ cation program, it will require applying several more treatments (2 or even more), that will require use ofseveral tons ofArndro™, even ifbait applications are focused on drierperiods oftheyear. As the infested area includes important parts of dense bush and steep slopes also, efficient bait utilization will also be impaired (a systematic baiting grid could not be 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 to successful eradication of an introduced species: 1) resources must be sufficient to fund the program to its conclusion; 2) the lines ofauthority must be clear and must allow an individual or agency to take all necessary actions; 3) the biology of the target organism must make it susceptible to control procedures (dispersal ability, reproductive biol­ ogy...); 4) reinvasion must be prevented; 5) the invader should be detectable at relatively low densities, to have early detection before it becomes widespread; 6) restoration or management of the treated community may often be required after process oferadicating (because of the impact on nontargeted species). Most ofthese requirements are not achieved in Vanuatu, no eradica­ tion attempt can thus be recommended, as it will involve high costs for hypothetical results. The risk offurther reinvasions appear high. Other entrypoints than those so faridentified mightalso existin the northem islandsofVanuatu: people move frequently with smallboats, transport­ ing plants, from island to island. Slowing the rate of spread might be more 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 the ants, pour hot water on them, pour oil or petrol around homes. sometime baitthemwith food and eitherbum the gatheringantsorpoor hot water on them. But these measures do not provide efficient control and the ants soon re-invade the treated area. Most effective control can be achieved by the use ofpoison baits, instead ofcontact insecticides. because it is brought back to the nest and kill brood and queens. In a control program, one must distinguish between public health and comfort, agriculture needs and natural environment concerns. To provide reliefto people in infested areas, control restricted to homes and in their vicinity could be achieved by the adequate use of insecticides. T The use of a commercial bait like Arndro " seems appropriate to this objective (Williams & Whelan 1992; Petty & Manicom 1995). Altema­ tively, spraying the soil, walls and roofs with pyrethrins could provide an appreciated relief but will not provide effective control. Baits and sprays must never be used at the same time. When no insecticide is available, simple tricks can provide reliefto sleepers, like isolating the feet ofthe beds with tin cans filled with mineraI oil, or using a sheet as a tent over the beds to prevent the ants from falling from the roof (as observed in many houses in infested areas). The same chemical control techniques could be applied to gardens and fruit trees, butthe high cost ofpoisonbaits will probablynot allow large field use. Also, Arndro™ baits •

496 Sociobiology Vol. 40, No. 3, 2002 could be inefficient under rainy conditions (Chazeau et al. 2000). Spraying of contact insecticides to kill the ant workers only when necessary (before harvesting the crops...) could also be done. A cheaper T alternative for trees istouse coconutoil and insecticiderings (Diazinon ") around the trunks, to prevent little fire ants' access to branches and fruits (Cochereau & Potiaroa 1994). Not much seems feasible in the invaded natural areas, so the only recommendation is to delay the invasion of free areas by a serious prevention policy. As pointed out for Solenopsis invi.cta and Linepithema humile in the USA (Porter et al. 1997; Holway & Suarez 1999), transplantation out of native areas should result in a competitive advantage for the invader, because it escapes from its own parasites, predators and native competitors. ltalso maximizes its habitat exploitative capabilities. But to date. no parasite or predator can be recommended for the biological control of W. auropunctata. Competition with other ants. especially other tramp species. could help in the control of the little fire ant. Pheidole megacephalacan efficientlycompetewith W. auropunctataand probably contributes to the containment by blocking entry points, as indicated byobservations in Santo and Mota Lava. Delabie et al. (1995) have shown a negative association between W. auropunctata and P. megacephala in habitations in Brazil. Sorne observations in New Caledonia indicate fierce competition between W. auropunctata and P. megacephalaat leastin inhabited areas (Jourdan 1999). Analogies can be found withthe competitive replacementbetweenP. megacephalaand L. humilein Madeira (StoIl1898). in Bermuda (Haskins & Haskins 1965, 1988; Liberburg et al. 1975), or in Hawaii (Cole et al. 1992; Wetterer et al. 1998). But one must remember that P. megacephala is also a tramp ant, which favors coccids and is considered as a serious pest in the 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 the ant fauna in Vanuatu. Such information will help in the search of potentialcompetitors asweIl asassessingthe rangeofthreatened fauna (using ants as bioindicators of the threats). From literature. we record only 46 species (in 28 genera) from the whole archipelago. lt includes 3 endemics but 2 subspecies. as weIl as 14 introduced species. including W. auropunctata (Table 4). Vanuatu ant taxonomic data are scattered and there is an inventory bias toward northern Vanuatu. especiallyEspiritu Santo and Malekula (39 species recorded from these 2 islands). In turn. the ant fauna richness appears very low and underestimated 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

Ponerinae Amblyopone australis Erihson, 1842 Tanna Wilson (1958a) N Anochetus graeffei Mayr, 1870 Espiritu Santo Wilson (1959a) N? c.... Hypoponera confinis (Roger), 1860 Panera confinis Malekula Wilson (1958b) I? 0 c Hypoponera pruinosa (Emery), 1900 Ponera pruinosa Espiritu Santo, Vanua Wilson (1958b) N a. Lava, Malekula Il> .:J Hypoponera punctatissima (Roger), 1859 First identified as Ponera Tanna Wilson (1958b), ~ gleadowi Taylor (1987) Leptogenys foreli Mann, 1919 Leptogenys walkeri , Espiritu Santo Donisthorpe (1942), N ~ tlJ Wilson (1958a) :- Leptogenys hebrideana Wilson, 1958 Espiritu Santo Wilson (1958a) E r Odontomachus simillimus Smith F., 1858 First identified as Efate, Aore, Espiritu Emery (1914), Wilson N? a Odontomachus haematoda Santo, Mata Lava (1959a), this study CD "Tl Pachycondyla darwinii (Farel), 1893 Trachymesopus darwini Efate, Espiritu Santo Wilson (19586) N? ~. Pachycondyla stigma (Fabnicius), 1804 Trachymesopus stigma Espiritu Santo Wilson (1959b) N » Ponera c1avicomis Emery, 1900 Espiritu Santo, Malekula Wilson (1957) N 3- Ul Ponera incerta (Wheeler WM), 1933 Ponera ratardorum Espiritu Santo Wilson (1957) N "0 éD Dolichoderinae a.Il> CIl Ochetel/us glaber (Mayr), 1862 Iridomyrmex glaber Espiritu Santo Emery (1914) N S' Tapinoma melanocephalum (Fabricius), 1793 Tapinoma melanocephalum Espiritu Santo, Tanna, Sanstchi (1928), Jourdan 1 ô < australe Efate (unpublished) Il> :J Tapinoma indicum timidum Santschi, 1928 Espiritu Santo Sanstchi (1928) E C Il> Technomyrmex albipes (Smith F.), 1861 Efate Jourdan (unpublished) 1 ë Tumeria dahlii Farel, 1901 Espiritu Santo, Malekula Shattuck (1990) N Tumeria pacifica Mann, 1919 Espiritu Santo Shattuck (1990) N

l' IR1rgglsl"gQj~J'~Iati"iIii' liiRQ91+1il: .j:>. Table 4 (cont.). List ot ant species recorded trom Vanuatu. (l) (Xl Synonyms Localities References Status

Formicinae Anoplolepis gracilipes (Smith, F.l. 1857 Anoplolepis longipes Etate, Espiritu Santo, Vanua Lava, Mota Emery (1914), this study Lava, Gaua Brachymyrmex obscurior, Forel 1893 Etate Jourdan (unpublished Camponotus chloroticus (Emery), 1897 Camponotus maculatus Espiritu Santo, Emery (1914) N chlorotica chlorogaster en Camponotus conithorax Emery, 1914 Etate, Malekula Emery (1914) N 0 () Paratrechina longicornis (Latreille), 1802 Tanna, Mota Lava, Jourdan (unpublishedl. 1 ô' 0- Espiritu Santo this study ô' 5" Paratrechina vividula buxtoni Santschi, 1928 Espiritu Santo Santschi (1928) E co Polyrhachis aurea fiorii Emery, 1914 Aoba Malekula, Emery (1914) N '< < Polyrhachis sericata (Guérin Méneville),1831 ? Wheeler (1935) N Q.

.j:>. Myrmicinae .0 Crematogaster (Orthocrema) spp. Espiritu Santo, Mota Wilson (1976), this study N z 9 Lava, Gaua 5.J Monomorium floricola (Jerdon), 1851 Malekula, Espiritu Bolton (1987) f\) 0 Santo, Erromango 0 f\) Monomorium pharaonis (Linnaeus), 1758 Malekula Bolton (1987) 1 Myrmecina sp. Espiritu Santo Wilson (1976) N Pheidole megacephala (Fabricius), 1793 Etate, Tanna, Espiritu Jourdan (unpublished), 1 Santo, Vanua Lava this study Pheidole oceanica Mayr,1866 Espiritu Santo Wilson (1961), Wilson & N Taylor (1967) Pheidole sexspinosa Mayr, 1870 Espiritu Santo, Banks Wilson (1961), Wilson & N Taylor (1967)

1: Introduced; N: Native E: Endemie •

Table 4 (Cont.).List of ant speeies reeorded tram Vanuatu.

Synonyms Localities References Status

Myrmicinae (Cont.) Pheidole umbonata Mayr,1870 Espiritu Santo, Vanua c... Wilson (1961), Wilson & N 0 Lava, Mata Lava Taylor (1967), this study c a. Pristomyrmex sp. Espiritu Santo Wilson (1976) N 0> Rogeria stigmatica Emery, 1897 Rogeria stigmatica Espiritu Santo Kugler (1994) N .::::l ;r: sublevinodis Strumigenys emmae (Emery), 1890 Quadristruma emmae Espiritu Santo Wilson & Taylor (1967) 1 ~ Strumigenys rogeri Emery, 1890 Espiritu Santo, Etate Bolton (1983) 1 ~ Stmmigenys szalayi Emery, 1897 Strumigenys szalayi Espiritu Santo Wilson & Taylor (1967) N australis ra Tetramorium bicarinatum (Nylander), 1846 First identitied as Erromango, Maiekula Bolton (1977) ëiï Tetramorium guineense ::!1 iD Tetramorium insolens (Smith F.), 1861 Santo, Erromango, Bolton (1977) N » Malekula ;::. Tetramorium pacificum Mayr, 1870 Espiritu Santo, rJ) "0 Erromango, Malekula, Bolton (1977) N? iD 0> Etate, Aoba, Tanna, Cl. CI> Anatom 5' Tetramorium tonganum Mayr, 1870 Etate, Malekula Bolton (1977) N ô Vollenhovia denticulata Emery, 1914 Espiritu Santo Wilson & Taylor (1967) N < 0> ::::l Vollenhovia oblonga (Smith, F.), 1860 Espiritu Santo Wilson & Taylor (1967) N C 0> Wasmannia auropunctata (Roger), 1863 Vanua Lava, Mata This study 1 ë

1:Introdueed; N: Native E: Endemie •

500 Sociobiology Vol. 40, No. 3, 2002

Islands. with up to 180 speciesin 52 genera (Mann 1919. Wheeler 1935. Wilson & Taylor 1967, Taylor 1976, Bolton 1995) or Fiji with up to 110 species in 35 genera (Mann 1921, Wheeler 1935. Wilson & Taylor 1967, Bolton 1995. Dlussky 1995). Nevertheless, we can notice affinities with the Solomon's ant fauna (Turneria sp., Pristomyrmex sp., Myrmecina sp., Pachycondyla sp.) though Southern Vanuatu seems to have wider affinities with the New Caledonian fauna, as shown by Wilson (l959c) and further emphasiswith herpetofaunadata fromTannaisland (Bauer 1999). Containment measures. Thebiological and ecological characteristics ofW. auropunctatahave implications for its containment. Given its low capacity of dispersion, the riskofrapid natural spreadislow: massive matingtlightshave never been observed and colonies extend through budding (Ulloa Chacon 1990, Jourdan 1999). Spreading that way is always slow, probably much less than 500 m ayear (Meier 1994). The tinynests maybe found in any modest shelter. most often in soil crevices, under pieces ofwood or stones, or in liUer; they also can be found under bark or inepiphytes. But in W. auropunctata, a nest includes several queens with high fecundity (Ulloa Chacon 1990).These characteristics explainwhyrapid spreading means human mediated dispersion. Despite this low intrin­ sicdispersion capacity, longtermnatural spreadingmayoccuron sorne infrequent occasions (flooding and heavy rainfalls). Groups of W. auropunctatahave been seenfloating on streams. This mayresult in the colonization ofnew areas as witnessed in New Caledonia (Jourdan 1999) and as known for several neotropical ants (Jaffé 1993). including S. invicta(MorillI974) and L. humile (Barber 1916) spreadingin United States. Masses of W. auropunctata have been observed floating on the sea up to 1 km from the New Caledonian coast (Jourdan 1999). Nests on floating woods might allow the colonization of sorne islands as observed for Pheidole sp. in Brazil (Wheeler 1916). Given the geography ofVanuatu, the probability ofsuch dispersion processes appear to be low. The transportation of nests by human activities must be avoided. It is the only overseas dispersal way and also the only quick dispersal opportunity inside invaded islands. The invasion of Santo - and, of course, of Efate - should be absolutely avoided. Their agricultural activities are associatedwith a trade node role, thatwill soon contribute to disperse the invader in other islands. The restoration (through efficient quarantine measures) of isolation boundaries broken by human transport appears to be a realistic solution to prevent further spreading. Transportofsoil, timber, thatch, buildingmaterial, bunches Jourdan, H. et al. - Little Fire AnI Spreads into Vanuatu 501 offruits. furniture. etc. should be prohibitedbetween infested areasand free areasinthe invadedislands. as weIl asaround the Banksgroup and other islands. Ifsuch transportscannotbe avoided. a rapid assessment to confirm the absence of W. auropunctata in this material should be conducted prior to transport. as weIl as in the arrivaI area during the following weeks. Quarantine decision to spray the planes coming [rom the Banks should also reduce new invasion. even if spraying could be inefficient against W. auropunctata brood. Detection should be organized in order to allow a faster reaction to the invasion in every entry points and to provide a better appraisal of the ant dispersal on invaded islands. A standard baiting technique using soya oil baits (or othervegetal edible oil) couId be implemented by the staffinvolved in the detection program. The concept ofentry points must be extend to every island and a monthly survey of the stations. which may receive and dispatch plants. soils. litter ... from and to other islands. should be promoted to efficiently detect low populations. The nursery plantations and agricultural stations (plant collection and dispatching) in the archipelago should be involved and immediately start their own survey of transit areas. The 3 trading ships which calI to Santo and other islands (Maewo. Pentecost. Malekula) after calling to the Banks as weIl as the ship of the anglican Diocese of Melanesia which visits Vanuatu each year. calling from the Solomon. should be inspected; captains and crew should be seriously informed on the situation and on their responsibility in the quarantine process. Prevention through early detection and general awareness must be promoted. Traditional chiefs and people ofthe villages where the piers and airfields are located should be specially informed and deeply involved in the quarantine process. To get full cooperation from Vanuatu people. who frequently move inside and between islands. they should be made aware ofthe ant problems as well as to be informed on the reasons why they are highly concerned. It will require an intense and sustained campaign of information and awareness. especially on how small a nest can be and how easily itcan be transported. Frequent radio advice could be used. aswas efficiently done in the country for the Aspidiotus 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 banana bunches), seem appropriate for scholars as weIl as for general use. These printed stories should be widely distributed in the archipelago and will be necessary to inform the Banks villages which radio broadcasting cannot reach. Every structure interested in community programs 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 geo­ graphic, social, economic and technical realities of many neighboring countries are similar to Vanuatu. They thus should take lessons from this experience to prevent the spread of this exotic ant and to react before it becomes strongly established. ACKNOWLEDGEMENTS On a request of Vanuatu authorities, the Pacific Community Plant Protection Service funded this inspection in northern Vanuatu. The project was warmly supported by Dr. Jimmie Rogers and officiaIs of Suva-based Agriculture staff. 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