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data and nuclear microsatellite and
allozyme markers, Caldera et al . (2008)
showed convincingly that the source of S.
invicta in the southern USA was northern
Argentina near the city of Formosa. Using a
large panel of 66 microsatellites and mtDNA
markers, Ascunce et al . (2011) found evi-
dence for at least nine separate introductions
from the southern USA to Australia, Taiwan
and China. Thus, the southern USA has
served as an invasive bridgehead for the
spread of fi re ants into many new areas in
the last 10-20 years. And similar, although
less extensive, genetic work on the
Argentine ant, Linepithema humile , points
to northern Argentina as the source of USA
populations (Tsutsui et al. , 2001).
The odorous house ant, Tapinoma
sessile , is the most widespread native ant
across the USA where it is also one the most
common ants, infesting structures in many
regions of the country (Hedges, 1998).
Menke et al . (2010) conducted a large-scale
study of populations in both undisturbed
and urban habitats to determine whether
the urban pest populations were all
descended from the same source population.
Using mtDNA sequence data, these authors
determined that urban populations were
derived from local populations residing in
'natural' undisturbed habitats. There was
strong genetic differentiation across the
country, suggesting that T. sessile may be
composed of a number of different species
or subspecies. In addition, Menke et al .
(2010) showed that in both urban and
natural areas colonies exhibited variation in
their social structure, with small monogyne
(single queen per nest) colonies and larger
polygyne (multiple queens per nest) col-
onies occurring in both natural and urban
areas, although many colonies in urban resi-
dential areas had very large polygyne col-
onies with millions of workers and
thousands of queens. Thus it seems that
multiple lineages of T. sessile have invaded
urban habitats independently and this may
be due to the plastic nature of their colony
social structure in which colonies can have
one or many queens.
As mentioned previously, French popu-
lations of the subterranean termite R.
fl avipes were thought to be a distinct species
( R. santonensis ). Using both sequence data
from mitochondrial genes and microsatellite
markers, Perdereau et al . (2013) showed
that the most likely source of populations in
France was from southern Louisiana, prob-
ably introduced into France with the timber
trade during the 17th and 18th centuries
when this region was under French rule.
Studies of potential sources of invasive C.
formosanus in the USA using microsatellites
(Husseneder et al. , 2012) and mtDNA
sequence data (Austin et al. , 2006) have
pointed to southern China where this
species is native as potential sources but so
far no specifi c location has been conclusively
identifi ed. Using mtDNA data, Jenkins et al .
(2007) concluded that introduced popu-
lations of the invasive species C. gestroi in
the USA probably came from Singapore and
Malaysia.
Advancements in genotyping methods,
such as single nucleotide polymorphisms
(SNP) and in the statistical analyses of
phylogeographic data, can greatly improve
the understanding of the sources and
patterns of spread of invasive urban pests.
Such information should contribute to
existing knowledge of the routes through
which certain pests are moved around and
the factors underlying the spread of some
species. For example, identifi cation of the
source of current bed bug populations
should shed light on the factors promoting
insecticide resistance that has allowed this
pest to resurge worldwide. As described
above, studies of the population genetic
structure of urban pests can play an
important role in helping to determine
potential sources of invasive species. The
next section focuses on studies of the
population structure of urban pests and
their importance in shedding light on dis-
persal and reproductive biology.
Understanding Population Structure
Termites
Understanding the genetic structure of
populations is important in inferring
 
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