Host-choice experiments were carried out with rodent and bat ectoparasites on Ilha Grande, state of Rio de Janeiro, Brazil. We constructed experimental chambers that enclosed three different rodent or bat host species, and then introduced a selected set of ectoparasitic arthropods. When given the opportunity to choose among host species, the ectoparasites showed a strong tendency to select their primary hosts, and reject novel host species. These kinds of simple experiments can be valuable tools for assessing the ability of ectoparasites to locate and discern differences between host species, and make choices about which hosts to infest, and which hosts to avoid

Bergallo, Helena G.

Bittencourt, Emerson B.

Bossi, David EP

Esbérard, Carlos EL

Fontes, Angélica

Gettinger, Donald

Lareschi, Marcela

Martins-Hatano, Fernanda

Menezes, Vanderlaine

English

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Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of 
11-2005 
A method for testing the host specificity of ectoparasites: give 
them the opportunity to choose 
Carlos EL Esbérard 
Fernanda Martins-Hatano 
Emerson B. Bittencourt 
David EP Bossi 
Angélica Fontes 
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Authors 
Carlos EL Esbérard, Fernanda Martins-Hatano, Emerson B. Bittencourt, David EP Bossi, Angélica Fontes, 
Marcela Lareschi, Vanderlaine Menezes, Helena G. Bergallo, and Donald Gettinger 
761Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 100(7): 761-764, November 2005
A method for testing the host specificity of ectoparasites: give
them the opportunity to choose
Carlos EL Esbérard/+, Fernanda Martins-Hatano, Emerson B Bittencourt*, David EP
Bossi**, Angélica Fontes, Marcela Lareschi***, Vanderlaine Menezes, Helena G Bergallo,
Donald Gettinger****
Departamento de Ecologia, Ibrag, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20559-900 Rio de
Janeiro, RJ, Brasil  *Laboratório de Ixodides, Departamento de Entomologia, Instituto Oswaldo Cruz-Fiocruz, Rio de Janeiro, RJ,
Brasil **Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis-Ibama, Brasília, DF, Brasil ***Centro de
Estudos Parasitológicos y de Vetores, La Plata, Buenos Aires, Argentina  ****Laboratory of Parasitology, Department of Biology,
University of Central Arkansas, Conway, Arkansas, US
Host-choice experiments were carried out with rodent and bat ectoparasites on Ilha Grande, state of Rio de
Janeiro, Brazil.  We constructed experimental chambers that enclosed three different rodent or bat host species, and
then introduced a selected set of ectoparasitic arthropods.  When given the opportunity to choose among host
species, the ectoparasites showed a strong tendency to select their primary hosts, and reject novel host species.
These kinds of simple experiments can be valuable tools for assessing the ability of ectoparasites to locate and
discern differences between host species, and make choices about which hosts to infest, and which hosts to avoid.
Key words:  ectoparasites - host-specificity - experiments - small mammals - neotropics
In the opening address of the “First Symposium on
Host Specificity among Parasites of Vertebrates” in
Neuchatel, France, 1957 (Wenzel & Tipton 1966), Ernst
Mayr posed a number of questions about host specificity
that are still of great importance in the evolutionary biol-
ogy of parasites and vertebrates.  “Where does host speci-
ficity occur?  How strict is it?  What groups of parasites
are most host specific?  Why are some parasites highly
specific, others of rather wide distribution?”  Today, in
studies of neotropical ectoparasites, the answers to these
questions continue to be confounded by the same prob-
lems noted by Mayr and later lamented by Wenzel and
Tipton (1966).  An ectoparasite is considered host spe-
cific when it is associated with a single species of host
(monoxeny) or a group of host species that are closely
related phylogenetically (pleioxeny).  Both vertebrates and
their associated arthropods remain very poorly known in
many parts of the neotropics, and most of our information
is coming from large, extensive faunal surveys.  Without a
sufficient number of samples collected at the population
level, the taxonomy of both vertebrates and ectoparasites
is inadequate for many kinds of biological studies.  When
ectoparasites are collected from novel hosts, it can be the
result of unreliable host or ectoparasite identifications,
contamination of samples, or real biological events in eco-
logical or evolutionary time.
But survey data alone cannot be applied to the ques-
tion of whether strict host specificity is due to an inability
of the ectoparasite to survive on other host species, or
Corresponding author. E-mail: cesberard@terra.com.br
Received 12 July 2005
Accepted 21 October 2005
simply an inability to locate and disperse to another host.
An experimental approach is needed.  Reed and Hafner
(1997) conducted transfer experiments in the laboratory
to determine if mallophagan lice can survive and repro-
duce on non-related gophers, and found that these per-
manent ectoparasites can, in fact, establish on other hosts.
They concluded that host specificity was maintained by
a lack of opportunity for lice to colonize new hosts.
Tomkins and Clayton (1999) transferred host-specific
mallophagan lice reciprocally among the nestlings of four
species of cave swiftlets in the field in Borneo.  Because
the transferred lice did not survive well on new hosts,
they concluded that even if lice could colonize new hosts,
they could not acquire the resources for successful es-
tablishment.  However, many ectoparasitic arthropods are
more vagile than mallophagan lice, and may have better
opportunities to come in contact with novel hosts.  We
wanted to develop an operational experimental strategy
to evaluate the ability of ectoparasites to locate and dis-
cern differences between host species, and make choices
about which hosts to infest, and which hosts to avoid.  If
host specificity occurs because of a limited capability to
disperse among novel host species, when the barriers that
impede them are removed, ectoparasites should colonize
other hosts. However, if specificity occurs because of
adaptive constraints, (i.e., a reduction of parasite fitness
on atypical host species), then ectoparasites should pre-
fer their typical hosts. The objective of this paper is to
present a simple and original experimental method, easily
replicated, for testing the host choice preferences of ec-
toparasitic arthropods.
MATERIALS  AND  METHODS
The experiments were carried out from November 8-
14, 2002, in an area of Atlantic forest located on Ilha
Grande, a large island off the mainland of the coast in the
state of Rio de Janeiro (23° 05’ to 23°  15’S, 44°  06’ to 44°
762 Testing host specificity of parasites • Carlos EL Esbérard et al.
23’W), at a research facility, Centro de Estudos Ambientais
e Desenvolvimento Sustentável (Ceads) of the Univer-
sidade do Estado do Rio de Janeiro  A transect of 100-130
livetraps, and 5 or 6 mist nets set along an Atlantic Forest
stream provided, respectively, a daily supply of rodents
and bats.  We constructed closed experimental chambers,
where ectoparasitic arthropods were introduced and of-
fered a choice of three different vertebrate hosts, which
were placed in close proximity within the chambers, and
connected by a common nest substrate (rodents) or roost-
ing surface (bats).  The chambers were plastic garbage
buckets of 30 l capacity, each of which enclosed three
screen cages (3/4" mesh) that fit tightly within the bucket
(Fig. 1).  The edges of the lids were sealed with Tac-trap
to prevent the escape of ectoparasites, and small holes
were cut in the lids to provide some circulation of air within
the bucket.
placed into the bucket and the lid was secured.  After 10-
12 h, the rodents were removed from the holding cages,
etherized, and brushed.  The ectoparasites from each of
the three experimental hosts were collected and placed in
individual vials of 70% ethyl alcohol.
Bat experiments - Three phyllostomid bats that are
common in the study area,  Artibeus fimbriatus Gray, 1838,
Sturnira lilium (E. Geoffroy 1810), and Carollia perspi-
cillata (Linnaeus 1758), were used in the experiments.   Bat
nets were opened at dusk and captured bats were trans-
ported to the laboratory within individual cloth bags, trans-
ferred into the small plastic box, and lightly etherized.  The
streblid flies (Megistopoda aranea (Coquillet 1899),
Megistopoda proxima (Séguy 1926), and Strebla guajiro
(Garcia & Casal 1965) were then collected manually and
placed temporarily in small plastic vials.  Each bat was
thoroughly searched until all the flies were captured, then
were given a sugar solution orally.  The three experimen-
tal bat hosts (A. fimbriatus, S. lilium, and C. perspicillata)
were placed in the buckets first, and then the captured
flies were introduced through a hole in the top of the
bucket.  Because some streblids can fly (others are brac-
hypterous and apterous), we covered the entrance hole
with fine screening.  After 10-12 h, the bats were removed
from the holding cages, etherized, and brushed.  The
streblid batflies collected from the three experimental bats
were placed in vials of 70% alcohol.
Because we wanted to be sure that all the arthropod
individuals were removed from the host both before and
after the experiments, we chose to work with large
arthropods.  For rodents, we used laelapid mites of the
genus Gigantolaelaps and amblyopinine beetles; with
bats, we used streblid batflies.  Previous studies of the
rodent and ectoparasite fauna of Ilha Grande (Guitton et
al. 1986, Martins-Hatano et al. 2002, Bittencourt & Rocha
2002) have provided evidence of strong specificity of these
ectoparasites for their small mammal hosts.  G. goyanensis
is a host-specific ectoparasite of N. squamipes (also see
Furman 1972, Gettinger 1987); Amblyopinus sp. is spe-
cific to T. dimidiatus; Amblyopinodes sp. to O. dasy-
trichus.   For bats, we relied on the host records from large
ectoparasite surveys in Venezuela (Wenzel 1976), and stud-
ies of other areas in the Atlantic Forest Region that have
quantified the host associations of the arthropods uti-
lized in our experiments (Bertola et al. 2005).  Megistopoda
aranae is a host-specific ectoparasite of A. fimbriatus; M.
proxima is specific to S. lilium, and Strebla guajiro to C.
perspicillata.
RESULTS AND DISCUSSION
Over a five day field trip, we carried out six experimen-
tal runs with the rodents and their ectoparasites, and two
experimental runs with the bats and their ectoparasites
(Table). All groups of ectoparasites consistently chose
their natural hosts (i.e., the preferred host species as in
the literature) (Fig. 2).  In fact, they chose their natural
hosts at about the same percentage as is registered in the
literature (between 90 and 100% of the time).  Hence, it
was observed that most of the ectoparasite individuals,
when given an equal chance to choose between the three
Rodent experiments - Three small mammals common
to the study area, two murid rodents, Nectomys squamipes
(Brants 1827), Oxymycterus dasytrichus (Fischer 1814),
and the echimyid rodent, Trinomys dimidiatus (Gunther
1877), were used in the experiments.  During the early
morning, rodents captured in the field were brought into
the laboratory, placed in a small plastic box and
anesthesized with ether.  Each animal was brushed thor-
oughly with a toothbrush to remove the ectoparasites
(see Martins-Hatano et al. 2002 for further information on
ectoparasite collection).  An artificial nest substrate made
of strips of paper towels was placed in the bottom of the
bucket, and in the bottom of the wire holding cages, pro-
viding easy access for crawling ectoparasites to move
from nest to the rodent of choice. The removed ectopara-
sites were introduced into the bottom of the bucket, then
the wire cages, each holding a different species of rodent
(N. squamipes, O. dasytrichus, and T. dimidiatus), were
Fig. 1: experimental chambers, each of which enclosed three screen
cages that fit tightly within the bucket.  The edges of the lids were
sealed with Tac-trap to prevent the escape of ectoparasites, and
small holes were cut in the lids to provide some circulation of air
within the bucket.
763Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 100(7), November 2005
hosts, returned to the original host species.  These data
support the larger body of evidence coming from exten-
sive faunal surveys of neotropical ectoparasites and their
mammalian hosts, and indicate that the described experi-
ments can be used to evaluate the capacity of ectopara-
sites to distinguish among hosts in ecological time.
New experiments could be performed, testing the pref-
erences of ectoparasites for hosts of different sexes, age,
body size, or reproductive activity, as well as preferences
of different combinations of host taxa, perhaps even elimi-
nating the primary, or natural host. These experiments can
provide important supplementary and supportive infor-
mation for both historical and ecological studies of verte-
brates and their ectoparasitic arthropods.  However, some
suggestions can be made:  (i) when utilizing ectoparasites
of small size or with the ability to hold tightly to the host
skin or pelage, we recommend that the host is brushed
repeatedly to guarantee that all arthropods are removed
before the host is placed into the holding cages (another
possibility would be the use of insecticides to make sure
the host is clean before experiments, but this would re-
quire a detoxification period);  (ii) it may be possible to
obtain counts of the number, sex, and/or life stages of the
ectoparasites before placing them into the bucket, then
using a Berlese funnel to determining the number of living
arthropods left in the bottom of the bucket without choos-
ing a host, and the number of arthropods that died during
the experimental process (due to ether, manipulation, or
grooming by the vertebrate hosts); (iii) following the host
choice experiments, it may be possible to maintain the
vertebrates infested with atypical ectoparasites in captiv-
ity to verify the capacity of these arthropods to survive
and reproduce on novel hosts.
Determining the host specificity of a parasite is a very
complex problem, involving anatomical, physiological,
evolutionary, and behavioral adaptations.  Although these
preliminary experiments are simplified, and we have em-
ployed only the most basic treatments (i.e., lumping
laelapine mites and amblyopinine beetles in a single ex-
periment), we believe that the approach is original and
promising.  For example, ectoparasites can also have spa-
tial and temporal infestation preferences, choosing differ-
ent regions of the host body at different times of the day
(Bittencourt & Rocha 2002).  By varying the experimental
design, it may be possible to understand some of the com-
plicating factors that determine host specificity.
Experimental strategies have great potential for ap-
proaching ecological and evolutionary questions about
host specificity, but if they are not carefully planned and
carried out they can be dangerous. We believe that biolo-
gists should take a strong look at the ethics of manipulat-
ing host-ectoparasite associations in the field.  Because
many ectoparasites are vectors, or potential vectors of
zoonotic diseases, the transference of ectoparasites
among host species can have catastrophic consequences
in natural ecosystems.
ACKNOWLEDGMENTS
To the Council for International Exchange of Scholars (CIES),
the J William Fulbright Scholar Program, the interactive faculty
of the Department of Ecology, Universidade do Estado do Rio
de Janeiro, and Centro de Estudos Ambientais e Desen-
volvimento Sustentável (Ceads/Uerj) for bringing the authors
together for a course on vertebrate ectoparasites, and for pro-
viding the opportunity to carry out this research. CEL Esbérard
received a CNPq grant (Process 152910/2004-0) and HG Bergallo
received a productive grant.
TABLE
Host exchange experiments:  host species, n = number of animals brushed; Arthropods  = numbers of ectoparasites
infesting each host
Hosts species  Hosts number Quantity of arthropods tested
Rodents Gigantolaelaps goyanensis Amblyopinodes sp. Amblyopinus sp.
Nectomys squamipes 5 64 1 0
Oxymycterus dasytrichus 3   1 4 0
Trinomys dimidiatus 2   2 0 3
Bats Megistopoda aranae Megistopoda  proxima Strebla guajiro
Artibeus fimbriatus 3 7 0 0
Sturnira lilium 3 0 7 0
Carollia perspicillata 2 0 0 6
Fig. 2: percentage (%) of arthropods of three major taxonomic
groups preferring either their natural hosts, or a new host, when
given the opportunity to choose in experiments carried out with
rodents (Laelapinae and Amblyopinini) and bats on Ilha Grande,
state of Rio de Janeiro, Brazil.
764 Testing host specificity of parasites • Carlos EL Esbérard et al.
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A method for testing the host specificity of ectoparasites: give
them the opportunity to choose

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