Causton, Charlotte E.

Mieles, Alejandro

Roque Albelo, Lázaro

English

Aquatic Commons

_...-
NOTICIAS DE GALÁPAGOSDecember 2000 17
THE ANTS OF MARCHENA ISLAND, TWELVE YEARS AFTER THE
INTRODUCTION OF THE LITTLEFIRE ANT WASMANNIA AUROPUNCTATA
Lázaro Roque-Albelo, Charlotte E. Causton and Alejandro Mieles
INTRODUCTION
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 ants" in a campsite in Playa Negra (Fig.1).
This is probably the most aggressive species of inverte-
brate that has been introduced in the Galápagos 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 activ-
ities 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. auropuncta-
ta in two fishing camps, in Playa Negra, Marchena, but
she did not determine the area infested.
In 1993, the Galápagos 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 Fé 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 deter-
mined 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 infesta-
tion to between 1 and 1.5 ha (Garcia 1996).
In August 1998 (during the El Niño 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 Galápagos Islands.
0.3 0.6
Figure 1 Playa Negra, Marchena Island
0.9 Kilometers
----
i Collectíon sites
~W Siteof intrO(luction
I
I l' I Newborder(2000)
~:_border(1998}
~.. Marchena Island
~
..~
.'
."..,
¡
. dI
"
~
Marchena Island
,
"+"
18 NOTICIAS DE GALÁPAGOS No. 61
-_...~.-
-.-
~-.._-
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Ant Species Status 1919 1988 1993 1994 1996 1998 2000
Camponotus macilentus bidloensis E X X X X
Camponotus planus E X X
Paratrechina fulva N X X X
Tapinoma melanocephalum I X X X
Dorymyrmex piramicus albemarlensis E X X
Hypoponera beebe E X X
Cardiocondyla emery I X X
Cardiocondyla nuda I X X
Monomorium floricola I X X
Solenopsis globularia pacifica I X
Tetramorium simillimum I X
Wasmannia auropunctata I X X X X X X
Table 1. Ant species found on Marchena during seven expeditions. Status in the Archipelago: E
=
endemic; 1 ~introduced; N
=
native.
T
Number coIlectedAnt Species
Uninfested Infested
I
TI T2 T3 T4
Camponotu5 plallus I 1 O O O
Paratrechina ¡ulva 3 16 O 1
Tapillomamelanocephalum 8 4 O O
Hypopollera sp O 1 O O
CardiocondylaIluda 3 6 O O
Cardiocolldyla emery
I
92 46 8 6
Wasmannia auropullctata O O 2124 1390
Table 2. Ant abundance from pitfall traps placed in uninfested and infested areas.
METHODS
Fieldwork was carried out in August 1988 and May 2000
by CDRS and GNPS personnel at the south side of
Marchena (Playa Negra) (Fig. 1). Bait stations were used
in order to determine the are a infested by W auropunc-
tata. Hot dogs (frankfurters) marked with red flags were
placed every 5 m along a 50 m transect from the last
infestation point recorded on the previous visit. The
baits were checked after 30 minutes and additional baits
placed if little fire ants were recorded from the last bait
station along the transect. A Geographical Position
System (Garmin 12 CX) was used to calculate the infested
are a with a GIS Arcview programo
The ant fauna was collected using a variety of meth-
ods. We collected ants with bait traps (honey, tuna fish,
and frankfurters). These traps were checked after one
hour because aggressive species monopolized the baits.
Pitfall trapping, leaf litter sifting, and hand collecting
methods were also used. Samples of the ants collected
were preserved in 70% ethanol and transported to the
CDRS for identification. This material was deposited in
the CDRS entomological collection.
In May 2000, pitfall traps were used to obtain quan-
titative information about the ant community. Four
transects were established, two in the W auropunctata
infested area and two outside this are a (Fig. 1). Ten traps
per transect were placed along a line of 10 m. They
consisted of 500-ml plastic cups containing detergent,
formalin, salt, and water (two-thirds of the volume) as a
preservative. Traps were placed in the ground for two
days. Ant identification followed that of Bolton (1994,
1995), Wheeler (1919), and Wilson and Taylor (1967).
Two indices were chosen to measure species diversity,
namely the Margalef index (M.I.), which highlights rich-
ness in term of the number of species, and the Shannon
and Weaver index (H'), which emphasizes species
dominance.
RESULTS AND DISCUSSION
Ant diversity
Among the species we collected in 1998 and 2000 were
five new records for Marchena: Camponotus planus
Smith, Cardiocondyla emery Forel, Cardiocondyla nuda
(Mayr), Paratrechina fulva (Mayr), and Hypoponera beebe
NOTICIAS DE GALÁPAGOSDecember 2000
-----.---
(Wheeler). These are in addition to five species recorded
for the first time on Marchena in 1988 and 1993 by L.
Baert and S. Abedrabbo (unpublished and reported for
the first time in this paper): Tapinomamelanocephalum
(Fabricius), Monomorium floricola (Jerdon), Dorymyrmex
piramicus albemarlensis (Wheeler), Tetramorium simillimun
(Smith), and Solenopsis globularia pacifica Wheeler.
We found that many more species of ants exist on the
island than has previously been published. A total of 12
species have been recorded from Marchena (Table 1) out
of the 55 ant taxa recorded from the Galápagos Islands
(Wheeler 1919, 1924, 1933,Clark et al. 1982,Lubin 1984,
Pezatti et al. 1998). The ant fauna of the island is charac-
terized by a high number of tramp species. Among the
12 species encountered on Marchena, five are intro-
duced. Only four, C. m. bidloensis, C. planus, D. p. albe-
marlensis, and H. beebe are endemic to the Galápagos.
The remaining native species could have been intro-
duced to Marchena in recent years from the inhabited
islands or may have been missed previously.
When comparing the collections made in early
surveys with our recent collections, we noted a marked
increase of the species richness in the island. Two factors
could be responsible for this increase: a) the early
surveys were incomplete or lacked locality data, or b)
ants have continued to migrate to the islands by natural
means or have been introduced by humans. Although it
is difficult to answer this basic question, anecdotal
evidence can be discussed.
We suspect that some species were simply over-
looked by early collectors who visited the island (e.g., C.
planus and H. beebe). Unfortunately, we do not have
published records that mention how much time or effort
was invested in the early ant collections. Some records
also appear to be incorrect. For example, Wheeler (1919)
described C. m. bidloensis from material collected by the
"Albatross Expedition of 1899"; however, Slevin (1931)
and Linsley and Usinger (1966) do not report the visit of
the steamer Albatross to Marchena in its two Galápagos
expeditions (1888 and 1891). The material studied by
Wheeler was probably collected during the Hopkins-
Stanford Expedition in 1888 and 1889. However, it does
appear that their effort was restricted to a few hours,
since Marchena is not considered a special place for
collecting wildlife specimens. If this is true, species
which are localized would have escaped early collec-
torso For example, during our collection, pitfall traps
captured most of the species present at a site, but hand-
collecting and leaf-sifting techniques using a Berlesse
funnel collected more rare or localized species (e.g. H.
beebe).
Peck et al. (1998) documented the known introduced
insects in the Galápagos Islands, including ants. He
found a strong correlation between the species numbers
of introduced insects and the number of human inhabi-
tants per island.
Marchena was never inhabited, and has only been
19
visited by fishermen, scientists, Park guards, and some
tourists, with most visits being concentrated in Playa
Negra. Tramp ants ha ve a high capacity for reaching
isolated habitats because of their small size and the
strong relation with transport by humans. This permits
them to travel long distances and establish themselves
in remote islands. We propose that T. melanocephalum, T.
simíllinum, S. globularia, M. floricola, P. fulva, and W
auropunctata probably arrived in Marchena in camping
provisions and equipment.
Species diversity in the presence and absence of
W. auropunctata
In May 2000, pitfall trapping was the only method used
to determine the species density of ants, because our
aim was to identify ground species that can be influ-
enced by W auropunctata. There was a striking contrast
between ant communities in habitats where W aurop-
unctata was present and absent (Table 2, Fig. 1).
Wasmanniaauropunctata was collected in all traps in the
infested area. Meanwhile, a low number of other ant
species, P. fulva (1) and C. emery (14), were collected in
the infested area. This co-occurrence was also reported
by Clark et al. (1982) in certain areas of Santa Cruz
Island where W. auropunctata was dominant during the
wet season. In contrast, six species were collected from
the uninfected area, including the two species found in
the habitats occupied by W auropunctata. These species
were C. planus, T. melanocephalum, H. beebe, and C. nuda.
Although C. emery was dominant in the uninfected
habitat, it was not numerically as dominant as W. aurop-
unctata.
The exposure time of pitfall traps (two days) appar-
ently affected the collections. In some traps only a few
ants were collected, with some species represented by a
single specimen. However, on this trip it was not possi-
ble to leave the traps out for longer. In the future, pitfall
traps will be placed in the field for one week.
The results of the tests using the Margalef Diversity
Index and the Shannon Weaver Index confirm that there
was a greater species richness and equitability in areas
where W auropunctata was absent. The values from the
Margalef Diversity Index were 0.60 and 0.95 in the little
fire ant-occupied area, while in the uninfected are a they
were 1.97 and 2.15. A similar pattern was observed with
the Shannon Weaver Index (0.01 in the infested area and
0.25 and 0.45 in the uninfected area). The total number
of ants increased by about twenty times in the infested
area due to the high density of W auropunctata individ-
uals. On the other hand, representa tives of other ant
species dropped by 90% and species richness declined
by 50%, from 6 to 3 (Table 2). Similar impacts were
reported by Porter and Savignaro (1990) for Solenopsis
invicta Buren in Texas.
Oistribution of W. auropunctata on Marchena
During the El Niño event of 1998,17 ha of the vegetation
20 NOTICIAS DE GALÁPAGOS No. 61
surrounding Playa Negra was occupied by dense mats
of W. auropunctata. Two years later the infested area had
increased by 41% to 24 ha. The area of distribution
shows a marked increase from estimates made on trips
prior to 1998. Although high precipitation rates during
El Niño may account for a rise in ant numbers (high
rainfall leads to vegetation growth and increased prey
numbers), it is unlikely that it is responsible for such
dramatic population growth (1.5 to 17 ha in one year).
This may be due to the techniques that were used on
earlier trips. What is evident, however, is that the distri-
bution of W auropunctata in Marchena is expanding.
This ant typically infests vegetated areas. In Marchena,
vegetation covers 25% of the total are a of the island. If
this ant continues to spread at this rate, it could have a
high impact on the native invertebrate species, especial-
ly those that are localized in distribution.
Can we control W. auropunctata?
Two factors should contribute towards the success of
this project: (a) the area occupied by W auropunctata is
still relatively small and manageable, and (b) new
colonies are formed by colony budding, thus gene rally
restricting the dispersal capacity of this species to are as
immediately adjacent to existing colonies. During the
monitoring trip in May 2000, a project design to eradi-
cate W auropunctata from Marchena Island was elabo-
rated. Over the next four years, AMDRO", the ant bait
identified as most effective for W auropunctata in the
Galápagos Islands (Williams and Whelan 1994), will be
hand-spread over the infested area. Bait applications
will be carried out according to the results of a monitor-
ing program that will run parallel to the eradication
efforts. This program will be initiated in September
2000. It is expected that the project will run for four
years.
ACKNOWLEDGEMENTS
We are indebted to Sanford Porter for all his valuable
advice and input to this project, and for taking the time
to accompany us on our last trip to Marchena. We hope
that this is only the beginning of a long-term partner-
ship in solving the ant problem. We are very grateful to
Kyle Miller at Cynamide ¡Basf for the donation of
AMDRO@ and to Fausto Venegas for organizing its ship-
mento Many thanks to Léon Baert for sending the ant
specimens collected during his trip and to Julie
Callebaut for the help with Arcview. Lastly, we would
like to acknowledge the work carried on by Victor
Carrión and his team from the GNPS, our partners in
the project. This project is funded by the United Nations
Foundation and UNESCO.
LITERATURE CITED
Abedrabbo, S. 1994. Control of the little fire ant Wasmannia
auropunctata, on Santa Fé Island in the Galápagos Islands. In D. F.
Williams (Ed). Exotic ants biology, impact, and control of intro-
duced species, pp. 219-227. Westview Studies in Insect Biology.
Baert, L. 1988. Unpublished field trip report, Charles Darwin
Research Station.
Bolton, B. 1994. Identification guide to the ant genera of the world.
Harvard University Press, Cambridge. 222 pp.
Bolton, B. 1995. A new general catalogue of the ants of the world.
Harvard University Press, Cambridge. 504 pp.
Clark, D., B. Guayasamin, C. Paz mino, O. Donoso and Y. De Villacis.
1982. The tramp ant Wasmannia auropunctata: Ecology and effects
on ant diversity and distribution on Santa Cruz Island, Galápagos,
Ecuador. Biotropica 14 (3): 196-207.
Garcia, N. 1996. Control de invertebrados hormiga colorada
(Wasmannia auropunctata) y repatriacion de galapaguitos
(Santiago). Unpublished field trip report, Galápagos National
Park Service.
Hamman, 0.1981. Plant communities of the Galápagos Islands. Dansk
Botanisk Arkiv 34 (2): 1-163.
Linsley, E.G. and R.L. Usinger. 1966. Insects of the Galápagos Islands.
Proceedings of the California Academy of Sciences 33: 113-196.
Lubin, Y. 1984. Changes in the native fauna of GaJápagos Islands
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Biological Journal of the Linnean Society 21 (1-2): 229- 242.
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American Entomologist (winter): 219- 237.
Pezatti, B., T. Irzan, and D. Cherix. 1998. Ants (Hymenoptera,
Formicidae) of Floreana: Lost paradise? Noticias de Galápagos 59:
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decimates native ants and disrupts arthropod community.
Ecology 71: 2095-2106.
Roque, L and C. Causton. 1999. El Niño and the introduced insects in
the Galápagos IsJands: Different dispersal strategies, similar
effects. Noticias de Galápagos 60: 30- 36.
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field trip report, Galápagos National Park Service.
Lázaro Roque-Albelo, Charles Darwin Research
Station, Galápagos, Ecuador (e-mail: lazaro@fcdar-
win.org.ec). Charlotte E. Causton, Charles Oarwin
Research Station, Galápagos, Ecuador (e-mail: caus-
ton@fcdarwin.org.ec). Alejandro Mieles, Charles
Oarwin Research Station, Galápagos, Ecuador (e-mail:
aemieles@fcdarwin.org.ec).


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

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

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