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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 97, Num. 1, 2002, pp. 61-63
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Mem Inst Oswaldo Cruz, Rio de
Janeiro, Vol. 97(1) 2002, pp. 61-63
Trapping Triatominae in Silvatic
Habitats
François Noireau/*/+ , Fernando
Abad-Franch**, Sebastião AS Valente***, Artur Dias-Lima****, Catarina
M Lopes, Vanda Cunha, Vera C Valente***, Francisco S Palomeque*****, Carlos
José de Carvalho-Pinto******, Ítalo Sherlock****, Marcelo
Aguilar*******, Mario Steindel******, Edmundo C Grisard******, José Jurberg
Laboratório Nacional e Internacional de
Referência em Taxonomia de Triatomíneos, Departamento de Entomologia,
Instituto Oswaldo Cruz-Fiocruz, Av. Brasil 4365, 21045-900 Rio de Janeiro, RJ,
Brasil *Institut de Recherche pour le Développement UR016, Paris, France
**Pathogen Molecular Biology and Biochemistry Unit, Department of Infectious
and Tropical Diseases, LSHTM, London, UK ***Instituto Evandro Chagas, Programa
de Doença de Chagas, Ananindeua, PA, Brasil ****Centro de Pesquisa Gonçalo
Moniz-Fiocruz, Salvador, BA, Brasil *****Departamento de Biología, Pontifícia
Universidad Católica del Ecuador, Quito, Ecuador ******Departamento de
Microbiologia e Parasitologia, Universidade Federal de Santa Catarina, Florianópolis,
SC, Brasil *******Unidad de Medicina Tropical, Instituto Juan César García,
Quito, Ecuador
+Corresponding author. Fax: +55-21-2573-4468. E-mail: noireauf@ioc.fiocruz.br
Research supported by the CNPq, IRD, UNDP/World
Bank/WHO Special Programme for Research and Training in Tropical Diseases (grants
970195 and A00206), Fiocruz, Funasa, ECLAT network, the Cañada-Blanch
Foundation and the University General Hospital (Valencia, Spain).
Received 8 May 2001
Accepted 16 August 2001
Code Number: oc02010
Large-scale trials of a trapping system designed
to collect silvatic Triatominae are reported. Live-baited adhesive traps were
tested in various ecosystems and different triatomine habitats (arboreal and
terrestrial). The trials were always successful, with a rate of positive habitats
generally over 20% and reaching 48.4% for palm trees of the Amazon basin. Eleven
species of Triatominae belonging to the three genera of public health importance
(Triatoma,
Rhodnius
and Panstrongylus)
were captured. This trapping system provides an effective way to detect the
presence of triatomines in terrestrial and arboreal silvatic habitats and represents
a promising tool for ecological studies. Various lines of research are contemplated
to improve the performance of this trapping system.
Key words: Triatominae - trapping system - silvatic
environment - terrestrial ecotopes - arboreal ecotopes
The control of domestic vector species of Triatominae
is being successfully pursued in most of the Southern Cone countries and is
being developed in the Andean countries and Central America. In areas with successful
control programmes, report of silvatic species invading human dwellings leads
research to be focused on their original habitats. Observations on the ecology
and behaviour of these silvatic triatomines will assist in devising strategies
for control-surveillance in areas where they invade or colonize synanthropic
habitats (Schofield et al. 1999).
Understanding of the ecology and biology of Triatominae
in their natural habitats is fragmentary, principally because collection of
specimens is laborious and time-consuming. Light trapping may be effective in
open vegetation, but only small numbers of starved adults of those species that
are light-attracted can be captured. An alternative is meticulous "habitat
dissection" of the great variety of potential ecotopes where triatomines
breed, including hollow trees, palm tree crowns, bromeliads, rock piles, burrows,
and bird-nests. The few animal-baited trapping devices previously designed to
sample silvatic triatomines have yielded poor results (Rabinovich et al. 1976,
Carcavallo 1985).
Recently, the use of a simple trapping system
to collect silvatic triatomines was reported (Noireau et al. 1999, 2000). Here
we present results of the first trials of this trapping system in various ecosystems
and different triatomine habitats.
MATERIALS AND
METHODS
The traps consisted of small plastic containers
(250 or 500 cm3) closed with wire mesh and partially covered with
double-sided adhesive tape (Figure). They
contained a mouse as bait together with a small quantity of wood shavings and
food. Initially designed for collecting silvatic Triatoma in hollow trees,
the system was later applied to the capture and study of Rhodnius species
in palm tree crowns (Abad-Franch et al. 2000, Palomeque et al. 2000, Valente
et al. 2000).
This trapping system has now been tested in various
ecosystems (Chaco, Caatinga, Amazon basin, and subtropical humid forests) and
in four types of triatomine habitats (hardwood trees, palm trees, rock piles
and crags). Traps were suspended in hollows located in trunks and limbs of hardwood
trees, or were placed in the crown of palm trees, among rocks or inside crevices.
One to four traps were generally used for each site, depending on its dimensions
and the number of accessible triatomine shelters (hollows in the case of trees).
Four traps were usually set in each palm crown. Traps were commonly set in the
afternoon and inspected the next morning, approximately 15 h later, in order
to avoid the midday heat.
RESULTS
With the live-bait traps, some mouse mortality
was recorded (< 2%). It was generally due to the attack by ants and is avoidable
by covering the wire mesh with finer cloth. Results of the different capture
series according to the ecosystem and triatomine habitat are shown in Table
I. Trials performed in favourable habitats known to harbour triatomines
were always successful, with a positivity rate higher than 20% and reaching
33.7% in hardwood trees in the Bolivian Chaco, 38.5% in rock piles of the Caatinga,
and 48.4% in palm trees of the Ecuadorian Amazon basin. The apparent density
of insects per positive habitat was highest for palm trees in the Amazon basin
and West Andean foothills in Ecuador (12.5 and 10.2, respectively), and reached
6.8 in rock piles. Eleven species of Triatominae (six Triatoma, four
Rhodnius, and one Panstrongylus species) have been captured
with this method (Table I).
Results on the efficacy of the trapping system
are shown in Table II. The positivity rate
of traps was higher in palm crowns and rock crevices than in hollow trees. The
number of insects adhered to the tape was usually low (one or two insects) but
could reach high densities (> 10, and up to 51) in some palm tree crowns.
DISCUSSION
The increasing reports of silvatic triatomine
species invading (and sometimes colonizing) peridomestic and domestic habitats
endorse the need for research on their original wild populations and habitats.
The study of these habitats by means of traditional approaches (random manual
searches and dissection) is laborious and destructive, hampering the development
of more detailed studies. Hence, many of the characteristics of triatomine habitats
are often obscure and remain to be more thoroughly investigated (Romaña
et al. 1999, Gaunt & Miles 2000). Live-baited adhesive traps could help
overcome some of these problems.
Results of several independent studies presented
here suggest live-baited trapping provides a quick, simple and inexpensive way
to detect the presence of triatomine populations in silvatic habitats. Four
important triatomine ecotopes were successfully searched by this method. Other
terrestrial (burrows, bromeliads, tree root cavities) and arboreal habitats
(bromeliad epiphytes) remain to be investigated. Eleven species of Triatominae
were captured in various environments, suggesting that the system may be applied
to other species as well. Repeated series of captures in positive habitats increased
the number of bugs captured, allowing for a more accurate assessment of the
density of colonies. Starved bugs were more likely to be attracted by the bait;
thus, the proportion of bugs captured in each ecotope would be inversely correlated
to the nutritional status of the population. This study confirms that the nutritional
status of silvatic bugs is generally very poor and may explain the unsuccessful
results obtained by live-baited trapping in domestic habitat where triatomines
are commonly fed (Tonn et al. 1976, Noireau & Dujardin 2001). Using this
trapping system, the ecological (and economical) damage caused by felling and
dissecting trees to study associated triatomines may be avoided. With regard
to the capture of T. klugi in crag crevices, previous attempts using
light trapping and active searching in crevices were unsuccessful.
Live-baited adhesive traps represent a promising
tool to identify triatomine habitats that may thereafter be studied longitudinally
(including for instance the response of bug populations to variations in microclimatic
conditions or hosts, or to biological control interventions). By allowing the
capture of silvatic specimens, several entomological factors can be investigated
(e.g. geographic range, density and structuring of bug populations or species,
natural infection by trypanosomes etc.). Furthermore, our knowledge on the ecology
of these populations (association to specific habitats, behavioural differences
in relation to vertebrate hosts etc.) may benefit from this sampling technique.
Live-baited traps may help define "high-risk" ecotopes (e.g., containing
dense bug colonies of species displaying synanthropic behaviour and frequently
infected by Trypanosoma cruzi) nearby human dwellings, an important issue
in areas where invasion and re-infestation of houses by silvatic vectors hinder
long-term interruption of vector-borne transmission.
Various lines of research could be explored to
improve the performance of this trapping system. Replacement of the live bait
by a chemical attractant would make traps easier to handle in the field, and
could help reduce their size so that smaller ecotopes (hollow trees and rock
crevices) might be studied. Finally, the design of a trapping system for intra-
and peridomestic habitats could be of use for entomological vigilance after
control interventions.
ACKNOWLEDGEMENTS
To Michael A Miles for the revision of an earlier
version of the manuscript. To Teresa Gutierrez, Rosmary Flores, José
Luis Botetano, Carlos Carpio, Karyna Suárez, José Elson Abud de
Araújo, Carlos Alberto Rodrigues, Gilberto César Rodrigues and
Nélio do Nascimento Farias for their invaluable assistance in the field
work. To Laure Emperaire for reviewing the identification of trees and CJ Schofield
for the useful comments on the manuscript.
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© 2002
Instituto Oswaldo Cruz - Fiocruz
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