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Host-finding of Triatomine bugs

 

 

 

 

 

 

 

Triatomine bugs usually leave their refuge during the night to search for their host (Lent & Wygodzinsky 1979; Schofield 1979; Núñez 1987; Schofield & Dolling 1993; Schofield 1994). In different experimental setups Triatomine bugs were attracted using potential hosts such as a hamster (Núñez 1982), mice (Taneja & Guerin 1995, Rose & Boeckh 1996b), and humans (Rose & Boeckh 1996a/b). However, the role of individual stimuli such as heat and host odors, including carbon dioxide, is not entirely understood. Rose & Boeckh (1996a) demonstrated that breath is a major stimulus used in the orientation toward the host in Triatoma infestans. The work published so far has been conducted only in the laboratory.

"The olfactory and thermal senses reside chiefly in the antennae, which serve also to perceive air currents and contact" (Wiggelsworth & Gillet 1934). Mayer (1968) successfully recorded electrophysiological responses of singele cells in olfactory receptors on the antennae of Triatoma infestans towards breath, Bernard (1974) towards other host odors.

 

 

Warmth

 

 

 

 

 

 

 

 

 


 

Early findings by Hase (1932) with different species from Venezuela (Panstrongylus geniculatus, Rhodnius pictipes, and Eratyrus cuspidatus) already indicated that warmth is a major reason for the extension of the proboscis. Wiggelsworth & Gillet (1934) confirmed the dominant role of warmth for short distance orientation for Rhodnius prolixus. A warm test tube alone elicited probing.

Nicolle & Mathis (1941) also reported probing responses towards warm bodies by Triatoma infestans and Rhodnius prolixus. Over a short distance, a warm current of air was shown to be attractive for already active Triatoma infestans and to elicit probing (Wiesinger, 1956). However, it did not activate resting animals.

Núñez (1982) reported that nymphs of Rhodnius prolixus were not activated by warmth. In an olfactometer, they were only slightly attracted, compared to other host odors and carbon dioxide. This was interpreted as an indication that warmth plays only a smaller role in the orientation towards the host over longer distances. Lazzari & Núñez (1989) showed that Triatoma infestans nymphs are able to perceive radiant head and to distinguish between different temperatures of radiant heat sources. +++

During his studies of olfactory sensilla of Triatoma infestans, Mayer (1968) did not find any response when he increased or decreased the temperature near the receptor. Lazzari & Wicklein (1994) recorded electrophsysiological activity of the so-called cave-like sense organ in the antennae of Triatoma infestans in response to thermal stimuli.

     

Carbon dioxide

 

 

 

 

 

 

 

 

 

The role of carbon dioxide was first investigated by Wiesinger (1956). She concluded that a warm (36 - 40 °C) mixture of carbon dioxide and air is more attractive for T. infestans than warm air alone, both in the activation and orientation responses towards the stimulus source.

Núñez (1982) attracted nymphs of Rhodnius prolixus in an olfactometer with carbon dioxide. Rose & Boeckh (1996b) report similar findings for second instar Triatoma infestans. Both Triatoma infestans and Rhodnius prolixus also showed oriented responses towards carbon dioxide on a servosphere (Taneja & Guerin 1995).

Guerenstein et al. (1995) were able to attract Triatoma infestans using an aerobic cultures of yeast on saccrose. The attraction of these cultures was reduced when the cabon dioxide realesed was partially eliminated using potassium hydroxide. A warm carbon dioxide source was shown to be attractive for nymphs of Triatoma infestans in an enclsure resembling the natural environment of the bugs (Rose & Boeckh 1996a).

Mayer (1968) reports responses of olfactory sensilla towards carbon dioxide and carbon monoxide. However, these responses were not as strong as those towards breath.

     

 

Other host odors

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Other host odors also seem to play a role in host orientation. Wiggelsworth & Gillet (1934) state that during their experiments, some bugs also oriented towards the test tube at room temperature when it was covered with a fresh mouse skin. However, they failed to probe it. No evidence was obtained of either attraction or repulsion by moisture.

Núñez (1982) attracted nymphs of Rhodnius prolixus in an olfactometer using his fore arm. Hamster odors were still attractive when they were bubbled through a mixture of potassium hydroxide and water, thus removing both carbon dioxide and lactic acid. Indications that mice give off attractive odors are given by Torres-Estrada & Martínez-Ibarra (1993): They report that starving nymphs of Triatoma gerstaeckeri chose mice nests as a hiding-place, whereas fed animals preferred stone walls.

Taneja & Guerin (1995) showed oriented responses of nymphs of Rhodnius prolixus and Triatoma infestans on a servosphere towards rabbit urine odors. Rose & Boeckh (1996b) attracted second instar Triatoma infestans using worn socks as a stimulus source. In 1997, Taneja & Guerin reported that ammonia at doses of 3 to 17 ppb attracted Triatoma infestans nymphs on a servosphere. They had detected ammonia both in stale rabbit urine odors as well as in wetted papers with triatomine feces.

The olfactory sensilla studied by Mayer (1968) also showed responses to some chemicals associated with human breath odors (methanol, methane, furan, pyridine). However, these responses were not as strong as those towards breath. Bernard (1974) also reports electrophsiological responses of sensilla on the antenna of Triatoma infestans towards complex host odors (a finger, sweat), as well as individual chemicals such as lactic acid or butyric acid.

Taneja & Guerin (1997) recorded electroantennograms as well as electrophysiological responses of single receptor cells in Triatoma infestans nymphs towards ammonia.