Triatominae

The members of Triatominae (trī·ə′täm·ə′nē), a subfamily of Reduviidae, are also known as conenose bugs, kissing bugs or triatomines. Most of the 130 or more species of this subfamily are haematophagous, i.e. feed on vertebrate blood; exceptionally some species feed on other invertebrates (Sandoval et al. 2000, 2004). They are mainly found and widespread in America, with a few species present in Asia, Africa and Australia. These bugs usually share shelter with nesting vertebrates, from which they suck blood. All triatomine species are potential vectors of Chagas disease, but only those species (such as Triatoma infestans and Rhodnius prolixus) that are well adapted to live with humans are considered important vectors of the Chagas disease parasite Trypanosoma cruzi.

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The discovery

At the beginning of the 19th century Charles Darwin made one of the first to report the existence of triatomines in America in his Journal and Remarks, commonly known as The Voyage of the Beagle. The following is an extract of what he wrote on 25 March 1835:

"We crossed the Luxan, which is a river of considerable size, though its course towards the sea-coast is very imperfectly known: it is even doubtful whether, in passing over the plains, it is not evaporated and lost. We slept in the village of Luxan, which is a small place surrounded by gardens, and forms the most southern cultivated district in the Province of Mendoza; it is five leagues south of the capital. At night I experienced an attack (for it deserves no less a name) of the Benchuca, a species of Reduvius, the great black bug of the Pampas. It is most disgusting to feel soft wingless insects, about an inch long, crawling over one's body. Before sucking they are quite thin, but afterwards they become round and bloated with blood, and in this state are easily crushed. One which I caught at Iquique, (for they are found in Chile and Peru,) was very empty. When placed on a table, and though surrounded by people, if a finger was presented, the bold insect would immediately protrude its sucker, make a charge, and if allowed, draw blood. No pain was caused by the wound. It was curious to watch its body during the act of sucking, as in less than ten minutes it changed from being as flat as a wafer to a globular form. This one feast, for which the benchuca was indebted to one of the officers, kept it fat during four whole months; but, after the first fortnight, it was quite ready to have another suck." --- Note: Luxan is Luján de Cuyo.

There has been considerable medical speculation as to whether or not Darwin's contact with triatomines in Argentina was related to his later bouts of long term illness.

Discovery of triatomines relation with Chagas disease

"Knowing the domiciliary habits of the insect, and its abundance in all the human habitations of the region, we immediately stayed on, interested in finding out the exact biology of the barbeiro, and the transmission of some parasite to man or to another vertebrate".

Biological aspects

• Cycle:

Triatomines undergo incomplete metamorphosis. A wingless first instar nymph hatches from an egg and passes successively through 2nd, 3rd, 4th and 5th instars. Finally, the fifth instar turns into an adult, acquiring two pair of wings.

• Ecology:

All triatomine nymph instars and adults are haematophagous and require the stability of a sheltered environment where they aggregate. Most species are associated with wild nesting vertebrates and are named "sylvatic" triatomines. These live in ground burrows with rodents or armadillos, or in tree-dwellings with bats, birds, sloths or opossums. Few species (5%) live in human dwellings or in the surroundings of human houses (peridomicile) in the shelters of domestic animals, these are named "domestic" species. Many sylvatic species are in process of domiciliation ("semidomestic").

• Behavior:

Most triatomines aggregate in refuges during day and search for blood during night when the host is asleep and the air is cooler. Odors as well as heat guide these insects to the host. Carbon dioxide emanating from breath, as well as ammonia, short chain amines and carboxylic acids from skin, hair and exocrine glands from vertebrate animals, are among the volatiles that attract triatomines. Vision also serves triatomines for orientation. During night, adults of diverse species fly to houses attracted by light.

Adults produce a pungent odour (isobutyric acid) when disturbed, and are also capable to produce a particular sound by rubbing the rostrum over a stridulatory sulcus under the head (stridulation).

• Epidemiology:

Domestic and sylvatic species can carry the Chagas parasite to humans and wild mammals; birds are immune to the parasite. T. cruzi transmission is carried mainly from human to human by domestic kissing bugs; from the vertebrate to the bug by blood, and from the bug to the vertebrate by the insect's feces and not by its saliva as occurs in most bloodsucking arthropod vectors such as Malaria mosquitoes.

Triatomine infestation especially affects unkempt dwellings. One can recognize the presence of triatomines in a house by its feces, exuviae, eggs and individuals themselves. Triatomines characteristically leave 2 kinds of feces like strikes on walls of infected houses; one is white with uric acid, the other is dark (black) containing haem. Whitish or pinkish eggs can be seen in wall crevices. After having had a blood meal the insects sometimes show a limited mobility and can be identified easily.

Tribes, Genera and numbers of described species

• Alberproseniini
  • Alberprosenia 2
• Bolboderini
  • Belminus 9
  • Bolbodera 1
  • Microtriatoma 2
  • Parabelminus 2
• Cavernicolini
  • Cavernicola 2
• Linshcosteusinii
  • Linshcosteus 6
• Rhodniini
  • Psammolestes 3
  • Rhodnius 16
• Triatomini
  • Dipetalogaster 1
  • Eratyrus 2
  • Hermanlentia 1
  • Meccus 6
  • Mepraia 2
  • Nesotriatoma 3
  • Panstrongylus 13
  • Paratriatoma 1
  • Triatoma 67

Note: For a complete list of species see Galvão et al (2004)

Most important vectors

All 138 Triatominae species are potentially able to transmit T. cruzi to humans but the following five species are the most epidemiologically important vectors of Chagas disease.

• Triatoma infestans
• Rhodnius prolixus
• Triatoma dimidiata
• Triatoma brasiliensis
• Panstrongylus megistus

References

• Brenner RR,Stoka AM (1987) Chagas’ disease vectors. I, II and III. CRC Press. Boca Ratón

• Dujardin JP, Schofield CJ, Panzera F (2000) "Les vecteurs de la maladie de Chagas: recherches taxonomiques, biologiques et génétiques". Academie Royale des Sciences d'Ultre-Mer. Belgium.

• Dunston PA (1999) Assassin Bugs. Science Publishers Inc., Enfield, New Hampshire. 337 pp.

• ECLAT = European Community Latin American Network for Research on the Biology and Control of Triatominae

• Galvão C, Carcavallo R, da Silva Rorcha D, Jurberg J (2004) "A checklist of the current valid species of the subfamily Triatominae Jeannel, 1919 (Hemiptera, Reduviidae) and their geographical distribution, with nomenclatural and taxonomic notes". Zootaxa 202: 1-36 First pages

• Lent H, Wygodzinsky P (1979) "Revision of the Triatominae (Hemiptera, Reduviidae), and their significance as vectors of Chagas disease". Bull Am Mus Nat Hist 163:123–520

• Maldonado-Capriles, Jenaro (1990) "Systematic Catalogue of the Reduviidae of the World". Special Edition of the Caribbean Journal of Science. University of Puerto Rico, Mayaguez, Puerto Rico. 694 pp.

• Otálora-Luna F (2006) Chemosensory and behavioural adaptations for haematophagy in triatomine bugs (Heteroptera: Reduviidae). Université de Neuchâtel. Available from World Wide Web

• Rodrigues Coura J (2001) "In Honor to Herman Lent’s 90 Years and to his Major Contribuitions to the Memórias do Instituto Oswaldo Cruz". Mem Inst Oswaldo Cruz 96:1029-1032 Available from World Wide Web

• Sandoval CM, Duarte R, Gutiérrez R, Rocha DS, Angulo VM, Esteban L, Reyes M, Jurberg J, Galvão C (2004) Feeding sources and natural infection of Belminus herreri (Hemiptera, Reduviidae, Triatominae) from dwellings in Cesar, Colombia. Mem Inst Oswaldo Cruz 99(2):137-140 Available from World Wide Web

• Sandoval CM, Joya M, Gutiérrez M, Angulo VM (2000) Cleptohaematophagy of the Triatominae bug Belminus herreri. Med Vet Entomol 14(1):100-101

• Schofield CJ (1994) Triatominae: biology & control. Eurocommunica Publications. West Sussex. UK 80 pp.

• Schofield CJ (2000) "Biosystematics and evolution of the Triatominae". Cad. Saúde Pública. [online]. vol.16 suppl.2 [cited 06 May 2005], p.89-92. ISSN 0102-311X. Available from World Wide Web.

• Zeledón R (1981) El Triatoma dimidiata (Latreille, 1811) y su relación con la enfermedad de Chagas. Editorial Universidad Estatal a Distancia. Costa Rica

• Zeledón R, Rabinovich (1981) "Chagas' disease: an ecological appraisal with special emphasis on its insect vectors". Annu Rev Entomol 26:101-33 Available from World Wide Web