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The History of Little Fire Ant Wasmannia auropunctata Roger in the Hawaiian Islands: Spread, Control, and Local Eradication


Abstract and Figures

The islands of Hawaii have been the battleground for successive “invasion waves” by exotic ants for over a century. The arrival of Pheidole megacephala (Fabricius) (the big headed Argentine ant) in the late nineteenth century, was followed in 1939 by Linepithema humile (Mayr) (the Argentine Ant) and Anoplolepis gracilipes (fr. Smith), (the longlegged Ant) in 1953. The most recent arrival is the little fire ant (Wasmannia auropunctata Roger) which was first recorded in 1999. This paper chronicles the subsequent spread of W. auropunctata through the Hawaiian archipelago. Initially introduced and spread via the import and sale of nursery plants, W. auropunctata is now well-established on the island of Hawaii. Ubiquitous on the windward side of Hawaii island, W. auropunctata are now being transported not only via nursery plants but also via non-agricultural products. The prevention, detection and response to W. auropunctata introductions is addressed by informal and ad hoc partnerships between a number of agencies, each contributing to preventing and reducing spread of this species. The draft Hawaii Inter-Agency Biosecurity Plan recognizes and strengthens these partnerships and will contribute positively to Hawaii’s biosecurity system.
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History of Wasma nnia auropunctata in Hawaii 39
The History of Little Fire Ant Wasmannia auropunctata Roger
in the Hawaiian Islands:
Spread, Control, and Local Eradication
Casper Vanderwoude1, Michelle Montgomery, Heather Forester,
Ersel Hensley, and Michael K. Adachi
Hawaii Ant Lab, Pacic Cooperative Studies Unit, University of Hawaii at Manoa,
16 E. Lanikaula St Hilo, Hawaii. 1Corresponding author:
Abstract. The islands of Hawaii have been the battleground for successive “inva-
sion waves” by exotic ants for over a century. The arrival of Pheidole megacephala
(Fabricius) (the big headed ant) in the late nineteenth century, was followed in 1939
by Linepithema humile (Mayr) (the Argentine ant) and Anoplolepis gracilipes (fr.
Smith), (the longlegged Ant) in 1953. The most recent arrival is the little re ant
(Wasmannia auropunctata Roger) which was rst recorded in 1999. This paper
chronicles the subsequent spread of W. auropunctata through the Hawaiian archi-
pelago. Initially introduced and spread via the import and sale of nursery plants,
W. auropunctata is now well-established on the island of Hawaii. Ubiquitous on
the windward side of Hawaii island, W. auropunctata are now being transported
not only via nursery plants but also via non-agricultural products. The prevention,
detection and response to W. auropunctata introductions is addressed by infor-
mal and ad hoc partnerships between a number of agencies, each contributing to
preventing and reducing spread of this species. The draft Hawaii Inter-Agency
Biosecurity Plan recognizes and strengthens these partnerships and will contribute
positively to Hawaii’s biosecurity system.
Key words: invasive ants, Hawaii, Wasmannia auropunctata, biosecurity, biologi-
cal invasions, Pacic, little re ant
Native ants are thought to be naturally
absent from the islands of the eastern
Pacic, including those of the Hawaiian
archipelago (Wilson and Taylor 1967). All
ant species currently recorded in Hawaii
are widespread cosmopolitan tramp spe-
cies that have been introduced by human
travel and commerce (Krushelnycky et al.
2005). The biota of Hawaii has evolved in
the complete or nearly complete absence
of ants, which most likely resulted in an
ecological predisposition to invasions by
exotic ant species along with increased
impacts such invasions may cause (Reimer
et al. 1990). The number of new ant species
has accumulated steadily over time to 47
(Krushelnycky et al. 2005), with the cur-
rent number of species a little higher due
mostly to taxonomic revisions.
Of these, four ant species are especially
noteworthy due to their ecological and
economic impacts worldwide, featur-
ing prominently in the IUCN list of the
world’s worst invasive species (Lowe et
al. 2000). The bigheaded ant (Pheidole
megacephala (Fabricius)) was rst re-
corded in Hawaii as early as 1879 (Smith
1879), at which time it was already well
established. In the years that followed,
proceedings of th e haWaiian entom ological so ciety (2016) 48:39–50
40 Vanderwoude et al.
entomologists lamented the dearth of na-
tive Coleoptera wherever P. megacephala
had become established (Perkins 1913).
Thei r association with mealybugs and
other common plant pests caused crop
losses, especially in pineapple (Beardsley
et al. 1982, Jahn and Beardsley 1994). In
the 1939, the Argentine ant (Linepithema
humile (Mayr)) was detected on the is-
land of Oahu (Zimmerman 1940, Reimer
1994). Primarily considered a nuisance
species, Argentine ants spread quickly
to the neighboring islands. The ensuing
battle for territory between L. humile
and P. megacephala saw the new invader
restricted to higher elevation habitats
where it caused considerable impacts to
native ecosystems (Medeiros et al. 1986,
Cole 1992, Krushelnycky and Gillespie
2008). In 1953, a new invader, Anoplolepis
gracilipes (fr. Smith) (the longlegged ant,
also known as the yellow crazy ant) ar-
rived at the US Naval base, Pearl Harbor
(Clagg 1953). A shade-tolerant species,
A. gracilipes thrived in shaded lowland
environments, preying on birds and in-
vertebrates (Gillespie and Reimer 1993).
Capable of episodic population explosions,
A. gracilipes forms dense super-colonies
that drive out other fauna and at some
locations, can cause the collapse of plant
communities (O’Dowd et al. 2003).
In 1999, the little re ant (Wasman-
nia auropunctata Roger) was detected
on the isla nd of Hawai i (Conant and
Hirayama 2000). This ant species has a
native range that includes South America
and the Caribbean (Wetterer and Porter
2003), but has invade d many Pacific
islands, West Africa, Australia, Florida,
and Israel (Wetterer 2013). Genetic com-
parisons with material from native and
introduced locations suggest Florida is the
putative source of the Hawaii introduction
(Mikheyev and Mueller 2007, Foucaud et
al. 2010). Here, we describe the spread of
this species through the Hawaiian islands
between 1999 and 2016 and discuss likely
introduction pathways.
Methods and Materials
We used published and unpublished
literature as well as personal commu-
nications and observations from others
involved with the response to this intro-
duction to document the spread of W.
auropunctata from the date of the initial
detection to the present (2016).
Histor y of Introduction
and Spread
The state of Hawaii is located in the
central Pacific Ocean, approxi mately
between longitudes 154–160° west, and
latitudes 19–22° north. It is made up of
eight separate islands, of which, six are
accessible by the general public: Hawaii,
Oahu, Maui, Kauai, Molokai, and Lanai.
Since the initial discovery in 1999, W.
auropunctata has become established on
the four most populous islands (Oahu,
Hawaii, Maui, and Kauai). The spread, to
and within, each island, is detailed below.
Hawaii island. In 1999, Conant and
Hirayama (2000) reported the presence
of W. auropunctata at 13 locations in the
South Hilo district on the island of Hawaii
(the Big Island). Initially, W. auropunctata
was observed on three infested proper-
ties in Hawaiian Paradise Park south of
Hilo. Soon thereafter, additional infested
locations were discovered at Kapoho
and Paipaikou. Most infested locations
were commercial nurseries or agricul-
tural properties that had recently planted
windbrea ks of Car yota sp. (fish-tail
palm) (P. Conant pers. com). Subsequent
public outreach, e.g. Gruner (2000), and
surveys revealed that W. auropunctata
infestations were more widespread than
rst estimated, likely spread through the
sale and movements of infested potted
plants. Despite this challenge and a lack
of resources, the Hawaii Department of
History of Wasma nnia auropunctata in Hawaii 41
Agriculture (HDOA) responded by treat-
ing all known infested properties with
baits. Between 1999 and 2007, the number
of separate known infestations increased
from an initial 3 properties to 56 by 2007
(Figure 1). These properties were scat-
tered between Kalapana (30 miles SE of
Hilo) and Laupahoehoe (25 miles NW of
Hilo) (Figure 2) spanning some 55 miles
to an elevation of 1,500 ft a.s.l.. However,
the actual number of infested properties
within these boundaries was probably
much higher (P. Conant, pers. com) as the
number of known sites was a reection of
survey effort, increasing levels of public
awareness and actual spread.
The widespread and mostly unknown
distribution of W. auropunctata, along
with an inability to treat colonies estab-
lished in the tree canopy (Souza et al.
2008), resulted in the continued spread of
this species. By early 2010, W. auropunc-
tata had spread to several locations on the
west coast of Hawaii island (Vanderwoude
et al. 2010). New infestations continued to
be detected beyond the original Kalapana-
Laupahoehoe area and now include most
of the west side of Hawaii island, Waipio
Valley, Hawi, Kapaau, Holualoa, Naalehu,
Captain Cook, and Waimea. In districts
with lower rainfall, W. auropunctata are
limited to favorable microclimates near
homes and other structures that feature
articial landscaping and irrigation (C.V.
pers. obs.). This concurs with the observa-
tions of Vonshak in Israel (Vonshak et al.
2010). By end 2010, the estimated number
of infested properties island-wide had
exceeded 4,500, growing to an estimated
6,400 by end 2012 (Lee et al. 2015). Figure
3 shows areas on Hawaii island currently
infested with W. auropunctata.
Kauai. At about the same time as the
initial detection (October 1999), plants
from an infested nursery on Hawaii had
been shipped to the island of Kauai. These
plants were infested with W. auropunc-
tata colonies. The plants and adjacent
1999 2000 2001 2002 2003 2004 2005 2006 2007
Figure 1. Number of known locations infested with Wasmannia auropunctata on Ha-
waii island between 1999 and 2007. Data sourced from Conant and Hirayama (2000);
Motoki et al. (Motoki et al. 2013), P. Conant (pers. com.) and informal reports from
Hawaii Department of Agriculture.
42 Vanderwoude et al.
Figure 2. Location of properties infested with Wasmannia auropunctata in January
2007 prepared by Hawaii Department of Agriculture.
areas were immediat ely treated with
baits to prevent further spread within
Kauai (Conant and Hirayama 2000). This
infestation was assumed eradicated. How-
ever, W. auropunctata were recorded in a
follow-up survey at the site four years later
in September 2003 (Null and Gundersen
2007). The infestation now covered ve
acres and had encroached onto an adjoining
property (see Figure 4). The site was treated
with granular baits followed by ad hoc
retreatment and periodic surveys through
to 2012. During these years, the infestation
spread mostly westwards eventually span-
ning 12 acres and extending down a steep
escarpment to Kalihiwai beach.
History of Wasma nnia auropunctata in Hawaii 43
Figure 3. Areas of Hawaii island currently infested with Wasmannia auropunctata
(2016). (Not all properties in the larger shaded section are infested).
Figure 4. Map of Kauai showing location infested by Wasmannia auropuntata (2012).
Currently this site is putatively ant free.
44 Vanderwoude et al.
Figure 5. Locations of all known sites on Maui infested with Wasmannia auropunctata.
In late 2012, a second eradication at-
tempt was implemented. At this time, the
critical issues of bait efcacy (Hara 2013,
Hara et al. 2014, Montgomery et al. 2015)
and arboreal treatment (Vanderwoude and
Nadeau 2009) had been largely resolved.
Due to the complexity of the site and
regulatory issues, this attempt was divided
into two phases: initially focusing on the
readily accessible areas and later address-
ing the escarpment and taller vegetation.
To date (late 2016), results are encourag-
ing. The entire site is putatively free of W.
auropunctata with only a single known
active colony detected beneath a taller
tree. Monitoring of this site and treatment
of the known small colony continues.
Maui. Wasmannia auropunctata have
been detected multiple times on the is-
land of Maui (Figure 5). The rst LFA
infestation detected on Maui was located
in Waihee, immediately west of the main
city of Kahului, in September 2009. A
resident reported receiving painful stings
from small ants on her property. Samples
of these ants were submitted to the HDOA
entomologist who conrmed it was Was-
mannia auropunctata. An inter-agency
taskforce was established, consisting of
staff from the County of Maui, Maui
Invasive Species Committee (MISC),
HDOA, US Geological Survey, Univer-
sity of Hawaii, and the Hawaii Ant Lab
(Hawaii Department of Agriculture 2009,
Vanderwoude et al. 2010). Together they
formulated an eradication plan which in-
cluded treatment, outreach and delimiting
elements (Vanderwoude et al. 2010). The
ants were restricted to a single property
and an island-wide delimiting survey of
probable high-risk sites did not nd addi-
tional infestations. The Waihee infestation
was ofcially eradicated in April 2014.
In December 2013, a Maui resident,
alerted by various outreach programs im-
plemented by MISC, found W. auropunc-
History of Wasma nnia auropunctata in Hawaii 45
tata on a hapuu log (Cibotium sp., a tree
fern) purchased from a local landscaping
supplier. The discovery prompted a larger
investigation by HDOA who discovered
that several shipments of hapuu logs, origi-
nating from the Big Island, were infested
(Hawaii Department of Agriculture 2013).
These shipments and subsequent distribu-
tion to retailers were located and inspected
by qua rant ine officers. A number of
these also had W. auropunctata. These
were either destroyed or treated in situ.
Two additional nascent infestations were
found in south Maui (Wailea area) during
the rst half of 2014 and these have been
eradicated by HDOA and MISC.
In September 2014, MISC eld workers
were stung by small ants while conduct-
ing other activities in Nahiku (near Hana,
Maui). These ants were later identied as
LFA and subsequent surveys found high
density LFA in challenging rainforest ter-
rain on both sides of the Hana Highway,
extending 1½ miles along a drainage to
the ocean. Four properties were involved.
The infestation appeared to have spread
downstream from an initial upstream
establishment point to the ocean. The
speed at which W. auropunctata spread
downstream was substantially faster than
normal lateral spread, most likely facili-
tated by the movement of infested debris
during periodic ooding events. Due to
the challenging nature of this infestation,
agencies collaborating on the response
(HAL, HDOA, Maui County and MISC)
formulated a containment and aggressive
control plan, rst removing LFA from
locations from which it would be likely to
spread, then to later assess the possibilities
for a more comprehensive approach. This
plan is ongoing.
Another LFA discovery was made
in Huelo in January 2015. An eradica-
tion plan has been developed and partly
implemented. Activities at this site were
hampered by the refusal of one resident
to allow treatment staff access. This re-
sulted in the HDOA taking the unusual
step of obtaining a court order (Hawaii
Department of Agriculture 2016), and later
declaring a quarantine on the property
in order allow the eradication program
to continue at this site. The delays to
treatment activities have allowed W. au-
ropunctata to recover and spread further
into this property, necessitating additional
treatment effort.
The site at Waihee, which had been
ant-free since 2010, was surveyed repeat-
edly between 2010 and 2014. In 2016
another survey was conducted at this site.
W. auropunctata were again detected in an
area immediately adjacent to the original
treatment area. It is possible that some
infested plant trimmings may have been
moved there before the original detection
in 2009. Only spanning an acre or so, this
site is now being treated again to ensure
no live ants remain.
Oahu. The detection of infested ship-
ments of hapuu in Maui prompted HDOA
to investigate other shipments from the
same suppl ier destined for Oahu and
Lanai. Some of these were also infested,
and as a result, HDOA staff systematically
surveyed the retail stores that received
these items. Several of these retail stores
also had become infested, and these were
systematically treated by HDOA staff
(Hawaii Department of Agriculture 2013).
The increased publicity surrounding
the infested hapuu led to the discovery
of two well-established infestations on
Oahu, each covering approximately ve
acres (Figure 6). One of these was lo-
cated in abandoned agricultural land in
Waimanalo and another in a suburban
area of Mililani. Eradication plans were
developed for each site and baits were
applied repeatedly to both sites over the
course of one year. One year after the last
treatment was applied (2016), both sites
are putatively free of LFA.
46 Vanderwoude et al.
The movement of W. auropunctata to
Maui and Oahu identied critical gaps in
the biosecurity system. On Oahu, these
gaps were addressed by implementing an
ongoing island-wide survey of high-risk
entry sites that began in January 2015 and
continues to the present. This program
was designed to complement existing
regulation and inspection systems, with
a goal to detect and eradicate infestations
while small. During the past two years,
this program has detected 16 nascent
infestations at Oahu nurseries which were
systematically treated. In late 2016 a large,
4-acre infestation was also discovered in
Waimanalo (not linked to the original
detection in the same district). Without
this early detection, such infestations will
grow too large to manage and become a
source-point for jump-dispersal to new
locations (Suarez et al. 2001).
The worldwide spread of invasive ants
began at least as early as the 16th century
(Gotzek et al. 2015). By the beginning of
the 20th century, the ecological impacts
caused by these invasions were becom-
ing apparent as entomologists lamented
the paucity of other invertebrate fauna
in locations invaded by ant species such
as Pheidole megacephala (Tryon 1912,
Perkins 1913). These invasions are widely
regarded as a consequence of human com-
merce (Wilson and Taylor 1967, Passera
1994, McGlynn 1999, Holway et al. 2002),
and in this regard, the recent introduction
and spread of W. auropunctata is no ex-
Queens and males in invasive W. auro-
punctata populations are mostly produced
th rough thelytokous par thenogenesis
(Fournier et al. 2005). Clonal reproduc-
Figure 6. Locations of known sites on Oahu infested with Wasmannia auropunctata.
(currently the infestation in Mililani and the original infestation in Waimanalo are
putatively ant-free)
History of Wasma nnia auropunctata in Hawaii 47
tion allows global invasion pathways of
this species to be accurately reconstructed
(Foucaud et al. 2010). Thus, the origin of
W. auropunctata in Hawaii can be attrib-
uted to W. auropunctata from Florida, as
one population is a clonal subset of the
other (Foucaud et al. 2010). Further, there
is an unambiguous connection with the
nursery trade as the original vector, both
for the initial introduction and subsequent
early spread within Hawaii island.
Potted plants are an ideal vehicle for
the movement of this species. The spaces
between the potting medium, plant roots
and the wall of plant conta iners are
convenient nesting sites, and forms a
moisture gradient that optimizes brood
development (Holldobler and Wilson 1990
p374). W. auropunctata colonies are small,
interconnected and typically possess a
worker:queen ratio between 250 and 500
(Ulloa-Chacon and Cherix 1990). This
virtually assures every plant within an
infested nursery houses a viable W. auro-
punctata colony which can remain largely
undetected. Further, by their nature, plant
nurseries are effective distribution points.
Together, these factors contributed to the
rapid spread of this species within Hawaii
Island, mirroring the historical spread of
this species through southern Florida via
the movement of potted plants and balled
citrus seedlings (Spencer 1941).
The pathways for movement of W.
au ropu nctat a betwe en the Hawai ian
islands have become more diverse as this
species became increasingly ubiquitous.
After the initial discovery in 1999, HDOA
further regulated the movement of plants
and propagative plant materials between
islands. Regulatory intervention included
a requirement for exporting nurseries to
be certied by HDOA, or for each ship-
ment to neighbor islands to be inspected
before shipment. Without this increased
watchfulness, the inter-island movement
of W. auropunctata would undoubtedly
have been much more rapid. However, at
least some of the multiple infestations de-
tected on Maui and Oahu are not linked to
the nursery trade in any way. For example,
no links between the purchase of potted
plants and infestations in Nahiku, Huelo,
Waihee and Mililani could be found.
The majority of ant-infested agricul-
tural commodities shipped between Ha-
waii Island and other islands is detected
and prevented from arriving by means
of a thorough and caref ul system of
regulation and inspection implemented
by HDOA. Inspection systems are based
on a risk-ma nagement approach that
utilize available resources to optimize
risk reduction. However, not all infested
commodities are (or can be) detected at
the border. As W. auropunctata become
increasingly ubiquitous on Hawaii island,
the variety and proportion of infested
cargoes increases beyond simply “nursery
plants” to include non-agricultural items
such as general cargo, household items
and vehicles. A percentage of infested
plants and other non-regulated material
will continue to arrive as a result of slip-
page (Whyte 2006)—infested goods that
bypass regulated pathways, escape detec-
tion or are in commodity categories that
are not inspected.
By its very nature, slippage is difcult
to quantify, and occurs in four commodity
classes: those that bypass the biosecurity
system, false negatives (infested material
inspected and cleared), commodities ex-
cluded from inspection and commodities
that do not fall within the HDOA man-
date (Government of Hawaii 1973). Not
all pathways are adequately regulated.
Air passengers carrying plants and other
propagative material between islands are
not inspected due to a lack of resources.
The rate of false negatives is likely to be
very low, but remains largely unknown.
Hawaii Administrative Rules (Hawaii Ad-
ministrative Rules 2012) limit commodity
48 Vanderwoude et al.
inspections to “plants and propagative
material.” The rules also acknowledge that
HDOA has legislative authority to inspect
a wider range of commodities such as foli-
age, cut owers and produce, but self-limits
activities to “periodic random inspec-
tions.” Finally, there are no systematic
inspections of other commodity classes
(used vehicles, machinery, household ef-
fects etc.) because HDOA does not have
legislative authority to do so.
Detection and response to these intro-
ductions demonstrates the complementary
roles of prevention through regulation
and inspection; early detection through
increased awareness and surveillance, and
rapid response through multi-agency col-
laboration. These elements of the Hawaii
biosecurity framework are performed by
different and sometimes multiple agencies
(Kraus and Duffy 2010) often through
semi-formal or ad hoc collaborations. Re-
gardless of the multitude of funding part-
ners, agency governance issues, obstacles
to data sharing, complex legal consider-
ations, and the often difcult operational
impediments, these collaborations can be
startlingly effective, as evidenced by the
rapid detection, response, and treatment
of multiple W. auropunctata infestations
throughout Hawaii. Of the eight infesta-
tions on the neighbor islands of Oahu,
Kauai and Maui, ve sites are putatively
free of W. auropunctata and the remain-
ing three are contained and continue to
be treated. A biosecurity plan that brings
these agencies closer and recognizes these
collaborations, is currently being drafted
by the State of Hawaii (Anon 2016), and
will serve as a blueprint for biosecurity
activities in the next decade.
As Wasmannia auropunctata spread
through the islands of Hawaii, the eco-
nomic and ecological impacts are likely to
be catastrophic. The predicted economic
costs to the island of Hawaii alone are
likely to exceed $100 million annually
(Lee et al. 2015). Continued prevention,
early detection and response to new incur-
sions on islands other than Hawaii island
is an invaluable investment in the future
of the unique and fragile ecosystems that
Hawaii has to offer.
The Hawaii Department of Agriculture
and Hawaii Invasive Species Council pro-
vide ongoing funding to the Hawaii Ant
Lab. The authors sincerely acknowledge
the contributions of HISC, HDOA, For-
est and Kim Starr the various Invasive
Species Committees, University of Ha-
waii, the Counties of Hawaii, Maui, and
Kauai, City and County of Honolulu, the
US Geological Survey, Department of
Lands and Natural Resources, the Pacic
Cooperative Studies Unit and all other
agencies and individuals that contribute
to the management of Wasmannia auro-
punctata in Hawaii. We thank P. Conant,
N. Reimer, K. Onuma, D. Arakaki, C.
Kaneshige and others who provided vital
anecdotal information.
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Full-text available
Wasmannia auropunctata (Roger) is an invasive tramp ant species that has been transported globally since [at least] the early twentieth century. It is often claimed that despite the negative impacts associated with this species and its listing among the world’s worst invasive species, very little research attention has been paid to W. auropuntata. Although the need for future research exists, there is currently a considerable body of research from around the world and spanning back to the 1920’s on this species. Here we synthesize over 200 peer reviewed research manuscripts, book chapters, conference presentations, and media reports of new distributions spanning 1929–2022 culminating in a comprehensive literature review on W. auropunctata. This review covers all current knowledge on this species and is intended to serve as a quick reference for future research and provide the reference resources for those seeking more in-depth information on specific topics. Topics included in this review include taxonomic identification, current global distribution and pathways, life history, impacts, detection, and control. We discuss where consensus and ambiguity currently lie within the research community, identify contextual considerations for future researchers when interpreting data, and suggest where we believe more research or clarifications are needed.
Full-text available
Acquisition and retention of two protein markers were tested on little fire ants, Wasmannia auropunctata Roger. Pure (100%) cow's milk and a dilution (10%) of chicken egg whites were applied to W. auropunctata directly by contact spray plus residue or indirectly via residual contact only with protein-marked plant debris. Protein-marked ants were held in plastic shoe-box-sized containers, collected at 0, 24, and 48 h after exposure to their respective marks, and then examined for the presence of the marks by a chicken egg albumin and milk casein-specific enzyme-linked immunosorbent assay. Cross-contamination rates were assessed by allowing ants marked with egg whites to interact with an equal number marked milk for 24 and 48 h, and then collected either individually or in bulk. Results indicated that the egg white biomarker was retained longer than milk and that more ants were successfully marked when the direct spray application method was employed. Cross-contamination rates were highest among bulk-collected ants and lowest among ants collected individually after 24 h. However, the rates of cross-contamination among individually collected ants increased and were similar to that of bulk-collected ants after 48 h. On the basis of our results, external protein marking may not be suitable if mass trapping is required or if the study extends beyond 24 h due to high cross-contamination rates among specimens collected in bulk and reduced marker detection rates.
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Biological invasions are largely thought to be contemporary, having recently increased sharply in the wake of globalization. However, human commerce had already become global by the mid-16th century when the Spanish connected the New World with Europe and Asia via their Manila galleon and West Indies trade routes. We use genetic data to trace the global invasion of one of the world's most widespread and invasive pest ants, the Tropical Fire Ant, Solenopsis geminata. Our results reveal a pattern of introduction of Old World populations that is highly consistent with historic trading routes suggesting that Spanish trade introduced the Tropical Fire Ant to Asia in the 16th century. We identify southwestern Mexico as the most likely source for the invasive populations, which is consistent with the use of Acapulco as the major Spanish port on the Pacific Ocean. From there, the Spanish galleons brought silver to Manila, which served as a hub for trade with China. The genetic data document a corresponding spread of S. geminata from Mexico via Manila to Taiwan and from there, throughout the Old World. Our descriptions of the worldwide spread of S. geminata represent a rare documented case of a biological invasion of a highly invasive and globally distributed pest species due to the earliest stages of global commerce.This article is protected by copyright. All rights reserved.
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Biological invasions are generally thought to occur after human aided migration to a new range. However, human activities prior to migration may also play a role. We studied here the evolutionary genetics of introduced populations of the invasive ant Wasmannia auropunctata at a worldwide scale. Using microsatellite markers, we reconstructed the main routes of introduction of the species. We found three main routes of introduction, each of them strongly associated to human history and trading routes. We also demonstrate the overwhelming occurrence of male and female clonality in introduced populations of W. auropunctata, and suggest that this particular reproduction system is under selection in human-modified habitats. Together with previous researches focused on native populations, our results suggest that invasive clonal populations may have evolved within human modified habitats in the native range, and spread further from there. The evolutionarily most parsimonious scenario for the emergence of invasive populations of the little fire ant might thus be a two-step process. The W. auropunctata case illustrates the central role of humans in biological change, not only due to changes in migration patterns, but also in selective pressures over species.
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The little fire ant, Wasmannia auropunctata, has been increasing in importance as an exotic pest. Here we review published and unpublished information on its distribution, ecology, impact, and control. Wasmannia auropunctata occurs throughout most of the warmer parts of the New World, from subtropical Argentina to subtropical Mexico and through much of the Caribbean, though it is not clear whether this species is native to this entire region. During the past century, exotic populations of W. auropunctata have become established in numerous other places, including the Galapagos Islands, West Africa (Gabon, Cameroon, and possibly the Republic of Congo and the Democratic Republic of Congo), Melanesia (New Caledonia, Solomon Islands, Vanuatu, and possibly Tuvalu), Polynesia (Wallis and Futuna and Hawaii), the mainland US (Florida and possibly California), and on subtropical Atlantic islands (the Bahamas and Bermuda). The latitudinal range of known outdoors populations of W. auropunctata is from 32o40'S in Argentina to 32o20'N in Bermuda. Wasmannia auropunctata is also a greenhouse pest in more temperate regions, such as England and Canada. In many areas, W. auropunctata can be a significant agricultural pest, not only stinging agricultural workers, but also enhancing populations of Homoptera. Homoptera cause damage both through sapping plants of nutrients and by increasing the occurrence of diseases, including viral and fungal infections. In addition, W. auropunctata has negative impacts on many animals, both invertebrates and vertebrates, though most reports on such impact have been anecdotal. The impacts of W. auropunctata populations seem to be most severe on tropical islands where it is not native, such as the Galapagos, New Caledonia, and the Solomon Islands. Reports of widespread blindness in both domestic and native mammals caused by W. auropunctata stings deserve serious attention. Chemical control of W. auropunctata may be possible for small exotic populations spread over a few dozen hectares or less. For large exotic infestations, the only hope for long-term control appears to be classical biocontrol.
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Control of invasive ant species has predominantly been through the use of granular baits. These baits are not suitable for ant species that nest in trees and vegetation such as Wasmannia auropunctata, recently introduced to the Big Island and Kauai, Hawaii. In recent years there has been an increasing interest in the use of gel and paste baits for control of some invasive ant species. However, application of these bait types is difficult and time consuming. Here we describe new application methods for gel and paste baits in arboreal situations.
Native to the Neotropics, Wasmannia auropunctata has spread to numerous other tropical and subtropical areas, where it is can reach extremely high densities and threaten the local biota. To evaluate the worldwide spread of W. auropunctata, I compiled published and unpublished specimen records from > 1700 sites. I documented the earliest known W. auropunctata records for 53 geographic areas (countries, island groups, major West Indian islands, and US states), including many with no previously published records: Anguilla, Antigua, Barbuda, Caicos Islands, El Salvador, Guam, Montserrat, Nevis, St Kitts, St Martin, and Texas. In the New World, W. auropunctata has a seemingly continuous distribution from central Argentina to southernmost Texas, suggesting that it may be native throughout this expanse. Wasmannia auropunctata has also spread throughout the West Indies and to peninsular Florida, though it is unclear which West Indian islands may constitute part of its native range. The earliest Old World reports of W. auropunctata, in the 1890’s, came from West Africa: Sierra Leone and Gabon. Although no additional records have come from Sierra Leone, W. auropunctata has spread broadly across Gabon and into neighboring countries, where it is a serious pest. In Oceania, the earliest records of W. auropunctata date to 1972 from New Caledonia and 1974 from the Solomon Islands. Pacific populations of W. auropunctata are actively spreading within these islands and to many other island groups. In the past decade, first records of W. auropunctata have been reported from several Old World areas, including the Central African Republic, Papua New Guinea, Australia, Guam, Italy, and Israel. Wasmannia auropunctata appears to still have much potential for future spread in the Old World.
Native to much of Central and South America, the little fire ant Wasmannia auropunctata has been rapidly spreading throughout the world. In its introduced range, W. auropunctata is frequently linked with drastic reductions of ant diversity; anecdotal reports of damaging attacks on vertebrates are also common. As it poses an ever-increasing threat to biodiversity, W. auropunctata has emerged as a model system for the study of ecological differences between native and invasive ant populations. These studies have been hampered by a lack of information on the genetic relatedness between native and introduced populations. By investigating the genetic structure of W. auropunctata populations, we provide a framework for conducting phylogenetically independent tests of differences between these ants in their native and invasive ranges. Phylogenetic analyses, based on the cox1/cox2 region of mtDNA, revealed at least three separate source populations of W. auropunctata distributed across two large clades. Much of the Caribbean region, presumably part of the native range, is inhabited by a clade of ants sharing very similar or identical mtDNA haplotypes, suggesting the possibility of multiple introductions or high levels of gene flow across that area. Most invasive populations in the Pacific were closely related to these ants. The invasive populations in Gabon and New Caledonia arise from another, relatively distantly related clade. Phylogenetically independent contrasts confirm McGlynn's (1999) observation that invasive W. auropunctata populations are smaller than native populations. Given the complex phylogeographical structure of W. auropunctata populations, future comparative work should correct for phylogenetic effects.
Islands can serve as model systems for understanding how biological invasions affect community structure and ecosystem function. Here we show invasion by the alien crazy ant Anoplolepis gracilipes causes a rapid, catastrophic shift in the rain forest ecosystem of a tropical oceanic island, affecting at least three trophic levels. In invaded areas, crazy ants extirpate the red land crab, the dominant endemic consumer on the forest floor. In doing so, crazy ants indirectly release seedling recruitment, enhance species richness of seedlings, and slow litter breakdown. In the forest canopy, new associations between this invasive ant and honeydew-secreting scale insects accelerate and diversify impacts. Sustained high densities of foraging ants on canopy trees result in high population densities of host-generalist scale insects and growth of sooty moulds, leading to canopy dieback and even deaths of canopy trees. The indirect fallout from the displacement of a native ‘keystone’ species by an ant invader, itself abetted by introduced/cryptogenic mutualists, produces synergism in impacts to precipitate invasional ‘meltdown’ in this system.