Gabriel Manrique

The role of water vapour in the orientation behaviour of the blood-sucking bug Triatoma infestans (Hemiptera, Reduviidae).

The behavioural response to water vapour of the haematophagous bug Triatoma infestans was analysed. Dry or humid discrete sources at different temperatures were used as stimuli for insects walking on a locomotion compensator. Humidity significantly increased the tendency of these bugs to orientate towards thermal sources. Furthermore, humid sources at room temperature were attractive to T. infestans, but this effect was limited to short-range distances. On the other hand, dynamic sources, i.e. airstreams carrying different water vapour contents did not affect the spontaneous anemotactic behaviour of this species, neither in sign (positive) nor in intensity. The anemotactic behaviour was also not influenced by the physiological water balance state of the bugs. Results are discussed in relation to the cues released by living hosts of triatomine bugs and in relation to their responses to air-currents.

Comparison of disturbance stridulations in five species of triatominae bugs

It has been observed that Triatoma infestans and Rhodnius prolixus females stridulate to reject copulatory attempts performed by males. In addition, triatomines stridulate when disturbed or handled. In the present study, the temporal structure and frequency spectra of vibrational signals produced by mechanically disturbed T. infestans, T. sordida, T. guasayana, R. prolixus and Dipetalogaster maxima were analysed and compared. The inter-ridge distances of the prosternal stridulatory organ of the same species were also measured. The frequency spectra and repetition rates were similar, despite individuals of these five species have different sizes, their stridulatory grooves have different inter-ridge distances, and also their vibratory signals exhibited different temporal patterns. The hypothesis that disturbance stridulations are non-specific signals and could function to deter predators was discussed.

Different stridulatory vibrations during sexual behaviour and disturbance in the blood-sucking bug Triatoma infestans (Hemiptera: Reduviidae)

Abstract Stridulatory vibrations produced by Triatoma infestans females were recorded for the first time as substrate-borne waves and under unrestrained conditions. In the context of sexual behaviour, non-receptive females stridulated to reject male copulatory attempts. Male-deterring stridulations consisted of long series of repetitive syllables, each composed of two chirps: rubbing the tip of the proboscis against the groove with a postero-anterior movement produced the upward chirp, and, with an antero-posterior movement, the downward chirp. Stridulations were also produced under restrained conditions, when bugs were clasped with forceps. Both male-deterring and disturbance stridulations were observed to differ in their syllable duration, repetition rate as well as in their main carrier frequency. Measurements of the inter-ridge distances along the whole stridulatory organ made it unlikely that differences in carrier frequency resulted from the use of distinct regions along the organ. More probable, bugs rub their proboscis at different speeds in order to produce either male-deterring or disturbance stridulations. For disturbance stridulations, the possibility that the frequency of highest vibration energy lies beyond the maximal sensitivity range of the receptors is discussed, and it is speculated that they have been shaped during evolution to deter predators.

Yeast culture volatiles as attractants for Rhodnius prolixus: electroantennogram responses and captures in yeast-baited traps

Responses to air currents carrying volatiles from yeast cultures were measured by means of electroantennograms (EAGs) in the haematophagous bug Rhodnius prolixus and we tested yeast-baited traps in the laboratory. The volatiles liberated by yeast cultures generated a clear electrophysiological response, much higher than that obtained during stimulation with clean air. The addition of yeast cultures to the traps dramatically increased overnight capture. A modification performed on the traps was effective for this species, as the bugs were immobilised once they fell into the device. Our results demonstrate that yeast culture volatiles are attractive for R. prolixus. The results obtained by means of electroantennogram techniques represent the first electrophysiological evidence of the perception of yeast volatiles by the antennae of a triatomine bug. We discuss the relevance of our results in view of currently used sampling techniques and control strategies.

Two different vibratory signals in Rhodnius prolixus (Hemiptera: Reduviidae)

In this study the substrate-borne stridulatory vibrations produced by Rhodnius prolixus females were recorded and analysed in two different behavioural contexts. In the context of sexual communication females spontaneously stridulated to reject copulatory attempts performed by males. These male-deterring stridulations were fully effective: out of 61 attempts, no copulation occurred. These stridulations consisted of short series of repetitive syllables, each one composed by a single chirp. In the context of defensive behaviour, bugs stridulated if they were clasped or restrained. These disturbance stridulations consisted of long series of repetitive syllables, each one composed by a series of short chirps and a long one. Male-deterring and disturbance stridulations differed in their temporal pattern and frequency spectra, having a main carrier frequency of about 1500 and 2200 Hz, respectively. As no differences in the inter-ridge distances along the whole stridulatory organ were found, the differences in the frequency between both signals could be explained on the basis of a different velocity of rubbing of the proboscis against the prosternal stridulatory organ. It was found that R. prolixus and the related species Triatoma infestans rubbed only the central region of the stridulatory groove (around 1/3 of the total length) to produce disturbance stridulations. The results are discussed in relation to previous work on vibrational sensitivity in R. prolixus and are also compared with results reported for T. infestans.

Feeding is not necessary for triggering plasticization of the abdominal cuticle in haematophagous bugs.

A simple device was used to quantify changes in the mechanical properties of the cuticle of Rhodnius prolixus and Triatoma infestans that take place when these insects feed, i.e., plasticization. Different stimuli were presented for 1min to test for their ability to trigger plasticization. These were: a blood meal, a Ringer solution meal, contact with a warm surface and thermal stimulation without such contact. Our results supplant any previous hypotheses that have supposed that the presence of food in the alimentary tract is necessary to evoke plasticization. We find that mere contact of the proboscis with a warm surface (without any food intake) is sufficient to trigger plasticization indistinguishable from that produced by a blood meal. Thermal stimulation alone, i.e., without physical contact, was not effective.

Dislodgement effect of natural semiochemicals released by disturbed triatomines: a possible alternative monitoring tool

ABSTRACT: The quick detection of domestic and peridomestic triatomines in their environments becomes difficult without the use of dislodgement substances that flush them out from their shelters. At present, tetramethrin 0.2% is being widely used in control programs. Although it is an efficient dislodging agent, its toxicity might affect the health of captured triatomines, of other insects and, to a lesser extent, of other animals, including humans. Here, we tested if semiochemicals released by disturbed adults of Triatoma infestans and/or Rhodnius prolixus can make larvae of the same species exit from their refuges. In a walking olfactometer we found that: 1) larvae of T. infestans were repelled by the odors released by disturbed adults of their own species and of R. prolixus, 2) larvae of R. prolixus did not change their behavior in the presence of odors released by adults of both species, and 3) activity levels were not modulated by these odors in any of both species. Besides, in pseudonatural conditions we found an increased flushing-out activity of larvae of T. infestans when their shelters were sprayed with isobutyric acid or 3-pentanol, and of larvae of R. prolixus when sprayed with 3-methyl-1-butanol. We succeeded in this work to dislodge larvae of triatomines from artificial shelters using natural volatile compounds, allowing the capture of live bugs for further investigations (e.g., xenodiagnosis or genetic studies) and favoring ecological aspects (e.g., minimizing environmental insecticide-contamination and non-targeted mortality).

Filling dynamics of the Brindley's glands in the blood-sucking bug Triatoma infestans (Hemiptera: Reduviidae).

The filling dynamics of exocrine defensive glands is an important component of the defensive capacity of an insect in its natural environment. We studied the filling state and reloading rate of the Brindleys glands in the haematophagous Chagas disease vector Triatoma infestans (Hemiptera: Reduviidae). Quantitative analyses of isobutyric acid, the main secretion component, were carried out with glands dissected from adults under different scenarios of development, number of discharging events and feeding conditions. The alarm-pheromone function of the gland secretion was also assessed in bioassays with conspecific nymphs. Although pharate adults have their glands completely developed, these were not full until imaginal ecdysis. If kept undisturbed, the adults maintained a constant gland load, and discharged about 75% of the gland contents upon one disturbance event. While the glands can be discharged several times, full replenishing was not complete after one week, unless the insect had access to food. The escape behavior of nymphs in bioassays correlated with the chemical analyses, with nymphs showing significant avoidance only toward gland discharges from undisturbed or disturbed/fed adults. The results are discussed in reference to the feeding frequency and gregarious behavior of T. infestans under natural conditions, which suggest a relevant role of the filling dynamics of the Brindleys glands in the intraspecific communication of the insect.

Compounds released by disturbed adults of the haematophagous bug Triatoma infestans (Hemiptera: Reduviidae): behavioural effects of single compounds and binary mixtures

Adults of the Chagas disease vector Triatoma infestans Klug (Hemiptera: Reduviidae: Triatominae), possess paired exocrine glands: the metasternal and Brindleys glands. Both glands are discharged by disturbed adults, releasing an alarm pheromone that elicits an escape response of larvae. The present study analyzes the individual (or combined) effects of some of the volatiles of the whole pheromone blend released under disturbance, searching for active compounds and for possible interactions (e.g. synergism, additive effects) between them. Using an experimental arena, different doses of components emitted by disturbed adults are tested against larvae. Larvae show escape responses to some of the acids, as well as to one alcohol, but no response to ketones. This is observed with certain doses of compounds from Brindleys glands (isobutyric, butyric and acetic acid; 2‐methyl‐1‐butanol), although the compounds tested in the present study that are produced by metasternal glands are shown to evoke random responses, suggesting that mainly Brindleys glands are involved in the alarm context. Two combinations of two individually repellent compounds (2‐methyl‐1‐butanol with acetic or isobutyric acid) evoke escape responses, although other combinations make the individual effect disappear. A different mixture of two individually repellent compounds (butyric and isobutyric acid) evokes attraction, although these are also host odours. The potential use of the active compounds released by disturbed adults to monitor triatomine populations is discussed.

Female choosiness and mating opportunities in the blood-sucking bug Rhodnius prolixus

We investigated the relationship between female choosiness and mating opportunities in the blood sucking bug Rhodnius prolixus . Rhodnius prolixus females exhibit active discrimination behaviour to male mating attempts which delays or prevents copulation. Female rejection behaviours can be beneficial if mating opportunities are readily available and the pool of males varies in their quality. Thus, the benefits of finding a better quality male may override the cost of rejecting a mating opportunity. Since the availability of mating opportunities is affected by the ratio of sexually active males to females, we randomly assigned focal pairs to arenas with a sex ratio biased toward males, females or without other individuals. More females exhibited rejection behaviour when conspecifics were present, however, no differences were found when the sex ratio was biased toward either males or females. We discuss possible explanations for these results and hypothesize about the adaptive function of female rejection behaviour.