Liléia Diotaiuti

THE PROCESS OF DOMESTICATION IN TRIATOMINAE

The Triatominae represent a subfamily of the Reduviidae defined on the basis of their bloodsucking habit and associated characteristics. At present, 128 species are formally recognised, grouped into 17 genera in 5 tribes. The majority are silvatic, associated with a wide variety of vertebrate hosts -particularly nest-building mammals and birds. Others occupy silvatic and peridomestic habitats such as chicken coops and goat corrals, and a few have completed the transition to domestic habitats where they may become important as domestic vectors of human Chagas disease. The most highly domesticated species, such as Triatoma infestans in Southem Cone countries, and Rhodniusprolixus in parts of the Andean Pact and Central America, are now being progressively controlled through regional and national initiatives designed to eliminate domestic populations by residual insecticide spraying. In recent years however, there have been increasing reports of other species establishing domestic colonies, and some, such as T. dimidiata, have even invaded urban and periurban residences. In many cases, the new infestations involve little-known species previously considered to be exclusively silvatic in habit, such as Paizstrongylus rufotuberculatus, RIiodnius stali, and Eragrus inucronatus in Bolivia (Noireau et al. 1995, Dujardin et al. 1998a), and Pgeniculatus in the Amazon region (Valente et al. 1998). It seems clear therefore, that the process of domestication in Triatominae is not only a historical event, but may be a generalised current trend within the subfamily (cf. Diotaiuti 1997). Here we present a general description of the evolutionary process, as a basis for discussion of the possible mechanisms involved and their likely consequences.

Ecology, evolution, and the long-term surveillance of vector-borne Chagas disease: a multi-scale appraisal of the tribe Rhodniini (Triatominae).

Chagas disease incidence has sharply declined over the last decade. Long-term disease control will, however, require extensive, longitudinal surveillance systems capable of detecting (and dealing with) reinvasion-reinfestation of insecticide-treated dwellings by non-domiciliated triatomines. Sound surveillance design calls for reliable data on vector ecology, and these data must cover different spatial scales. We conducted a multi-scale assessment of ecological and evolutionary trends in members of the tribe Rhodniini, including (i) a macroscale analysis of Rhodniini species richness and composition patterns across the Americas, and (ii) a detailed, mesoscale case-study of ecological and behavioural trends in Rhodnius neglectus and R. nasutus. Our macroscale overview provides some comprehensive insights about key mechanisms/processes probably underlying ecological and genetic diversification in the Rhodniini. These insights translate into a series of testable hypotheses about current species distributions and their likely causes. At the landscape scale, we used geometric morphometrics to identify dubious specimens as either R. neglectus or R. nasutus (two near-sibling species), and studied palm tree populations of these two vector taxa in five geographical areas. The data suggest that deforestation and the associated loss of habitat and host diversity might increase the frequency of vector-human contact (and perhaps Trypanosoma cruzi infection rates in vectors). Surveillance in central-northeastern Brazil should prioritise deforested landscapes where large palm trees (e.g., Attalea, Mauritia, Copernicia, Acrocomia or Syagrus) occur near houses. We anticipate that, by helping define the distribution patterns and ecological preferences of each species, multi-scale research will significantly strengthen vector surveillance systems across Latin America.

Operational aspects of Triatoma brasiliensis control

Vector control strategies against indigenous species is not easy, due to their capacity to reinvade treated premises from sylvatic ecotopes. Between August 1996 and December 1997 we conducted a study on reinfestation of houses after spraying in a county in the State of Ceará. Of 277 houses examined, 113 (40.8%) were infested (21.7% intradomiciliary and 35.4% peridomiciliary). Of the 433 Triatominae collected, 207 were Triatoma brasiliensis (49% of which intradomiciliary, with a mean of 1.8 insects/house) and 226 were Triatoma pseudomaculata (97% peridomiciliary). The age structure of the two indicated a univoltine development cycle for T. brasiliensis and two cycles per year for T. pseudomaculata. Four months after spraying with deltamethrin SC 25mg ia/m2, 9.7% of the houses were still positive, mainly with peridomestic infestations. Intradomiciliary wall bioassays showed persistence of the insecticide up to 9 months after spraying. Considering the high potential for recolonization of treated premises from sylvatic foci, we propose an operational strategy combining traditional evaluations and community-based surveillance with increased selective interventions and community education.

Chemical communication in chagas disease vectors. source, identity, and potential function of volatiles released by the metasternal and Brindley's glands of Triatoma infestans adults

Compounds from the metasternal and Brindleys glands of the blood-sucking bug, Triatoma infestans, were identified by solid phase microextraction (SPME) and gas chromatography-mass spectrometry. Volatile compounds released by adult bugs during copulation or after mechanical disturbance were also characterized. Six compounds were identified and found consistently in all samples from metasternal glands. The most abundant were 3-pentanone, 2-methylbutanol, 3-pentanol, and an unidentified compound. The metasternal gland blends did not differ qualitatively between sexes. Compounds found in Brindleys glands were short chain acids, alcohols, esters, and a ketone with no qualitative differences between sexes. Isobutyric acid was the main component of this blend, and two new confirmed compounds were described as products of these glands: 2-butanone and 2-methylbutyric acid. 3-Pentanone was collected from the headspace over 33% of the copulating pairs of T. infestans. Volatiles found in the headspace of disturbed T. infestans adults included short-chain fatty acids, alcohols, esters, and ketones, with no qualitative differences between sexes. Both types of glands apparently discharge their contents after disturbance. However, most of the volatiles released by bugs after disturbance came from Brindleys glands. The locomotor activity of fourth instars increased significantly after stimulation with the odors emitted by disturbed adults, as compared with larvae stimulated by the odor of undisturbed adults or by clean air. We also studied the directional behavioral response of fifth instars to the disturbance scent in a locomotion compensator. Larvae exposed to volatiles released by disturbed adults walked away from the direction of the odor. The results suggest that this blend or part of it functions as an alarm pheromone for T. infestans. We suggest that the metasternal glands of this species are involved both in the sexual and the alarm contexts, and that the Brindleys glands probably have both alarm and defensive roles.

Controle do Triatoma sordida no peridomicílio rural do município de Porteirinha, Minas Gerais, Brasil

Triatoma sordida, a predominantly peridomestic species, is currently the triatomine species most frequently collected in Brazil. To evaluate the effectiveness of control activities against this species, a survey to determine infestation rates was carried out in October 1993 in 12 rural localities in the municipality of Porteirinha, State of Minas Gerais, Brazil. In the survey, 772 T. sordida were captured, of which 3.6% were infected with Trypanosoma cruzi. Of the 406 dwellings investigated, 34.9% were infested, and 27.6% of 695 peridomiciliar ecotopes contained T. sordida. The area around the dwellings was relatively uniform, with few positive ecotopes per household and low triatomine densities (a maximum of five insects per colony). The study found an association between the presence of insects and wood: 72.8% of the insects were captured in this type of ecotope. The majority of the positive households (62.9%) were close to forests (12 to 299 m); 92.3% of the infested ecotopes were less than 20 m from the house. A census of peridomestic animals revealed that chickens were the most abundant (82.7%). All positive households found in the survey were sprayed immediately with deltamethrin (25 mg a.i./m2). New surveys were carried out 7 months (survey 2) and 12 months (survey 3) after spraying. In survey 2, the number of insects collected corresponded to 52.5% of the original total, and in survey 3, 79.1%. The decrease in population observed in survey 2 was mainly due to a reduction in the population of nymphs. The large proportion of adults captured in that survey supports the idea that T. sordida produces only a single generation per year in this region. In survey 3 the increase in the number of nymphs, attributable to the great availability of chickens as a source of food, resulted in population growth. Despite the difficulties of spraying and the short persistence of the insecticide, the slow population response of T. sordida suggests that one annual spraying is sufficient for effective control of this species. Higher effectiveness could be obtained by eliminating peridomestic hiding places, for example, by replacing wooden annexes with structures made from other materials.

Influence of the Blood Meal Source on the Development of Triatoma infestans, Triatoma brasiliensis, Triatoma sordida, and Triatoma pseudomaculata (Heteroptera, Reduviidae)

Abstract The objective of this study was to determine the influence of the blood meal source on the life cycle and reproductive development of female Triatoma infestans (Klug, 1834), Triatoma brasiliensis Neiva, 1911, Triatoma sordida (Stal, 1859), and Triatoma pseudomaculata Corrêa & Espínola, 1964. In all triatomine species studied the life cycle was shorter for the groups fed on mice than for those fed on pigeons, the range of differences being between 1.5 times (T. pseudomaculata and T. infestans) and 2.4 times (T. brasiliensis). The mortality rate of nymphs during the life cycle tended to be greater in insects fed on pigeons than in those fed on mice, the differences for T. brasiliensis being statistically significant. Females of T. sordida and T. pseudomaculata had a greater fecundity than those of T. infestans and T. brasiliensis independently of the blood meal source. The differences of fecundity observed probably reflect differences in the availability of blood in the silvatic ecotopes of these species, meals being more frequent for T. infestans and T. brasiliensis, which live at high densities in association with rodents in highly stable ecotopes. Because T. sordida and T. pseudomaculata live in more unstable ecotopes with fewer sources of blood they form small sparse colonies and invest more energy in reproduction than maintenance.

Feeding behaviour of morphologically similar Rhodnius species: influence of mechanical characteristics and salivary function.

Despite their morphological similarities, very similar Rhodnius species (R. prolixus, R. robustus, R. nasutus and R. neglectus) displayed a distinct feeding behaviour when fed on artificial feeder, pigeon or mouse. On pigeon hosts, these species showed distinct groups in terms of cumulative probing time - quicker species (R. prolixus and R. neglectus) followed by R. nasutus and finally a much slower species (R. robustus). On mouse hosts, R. nasutus showed quicker probing time compared to the other three species. Moreover, R. prolixus displayed quicker probing time compared to R. robustus and R. neglectus. Except for R. nasutus, the mean total ingestion rate tended to have different values between feeding sources (artificial feeder>pigeon>mouse). The volume ingested by each cibarial pump contraction and maximum frequency obtained using the artificial feeder are expected to be related to intrinsic mechanical characteristics of the insect feeding apparatus. However, probing time and the modulation of cibarial pump frequency on live hosts may be related to salivary function. R. prolixus showed high mechanical and salivary efficiency, achieving high values of total ingestion rate when fed on artificial feeder or either of the hosts. Comparative analysis suggests that species which possess higher total ingestion rates tend to achieve higher nutritional status, allowing them to reach higher densities.

Comparison of feeding behaviour of Triatoma infestans, Triatoma brasiliensis and Triatoma pseudomaculata in different hosts by electronic monitoring of the cibarial pump

Feeding behaviour of Triatoma infestans, T. brasiliensis and T. pseudomaculata on pigeons and mice was compared by electronic monitoring of the cibarial pump. The methodology developed permits the study detailed of triatomine feeding behaviour using an artificial feeder as well as on live hosts. T. infestans was the species that fed most rapidly on the two hosts tested (28.03+/-1.6 mg/min for pigeon and 21.33+/-1.7 mg/min for mouse), followed by T. brasiliensis (17.09+/-1.4 mg/min and 13.1+/-1.5 mg/min for pigeon and mouse, respectively) and T. pseudomaculata, (5.23+/-0.6 mg/min and 4.09+/-0.4 mg/min for pigeon and mouse, respectively). The quantity of liquid ingested per stroke of the cibarial pump was 100.7+/-4.1 nl for T. infestans, 69.1+/-2.7 nl for T. brasiliensis and 26.8+/-1.5 nl for T. pseudomaculata. The rate of engorgement in pigeons tended to be greater than that obtained for mice in the three species studied. In the experiments carried out using mice, probing times tended to be longer and interruptions during the meal more prolonged. This reinforces the idea that feeding on mice is more difficult than on pigeons, requiring more contact time to obtain the similar quantity of blood.

Some considerations about the ecology of Triatominae

Observations on the ecology of silvatic Triatominae are still fragmentary, principally because target species in control process are almost exclusively domestic. Report of silvatic species invading human dwellings must lead research to be focused on their original ecology, in order to assist in understanding their process of domestication and devising strategies for surveillance.

The effect of relative humidity on the behaviour and development of Triatoma brasiliensis

Abstract The preference for relative humidity (RH) and suitability of different levels of this environmental parameter were investigated in the haematophagous bug Triatoma brasiliensis Neiva, 1911 (Hemiptera, Reduviidae). The hygropreference of T. brasiliensis was studied using a RH gradient and the effect of different RHs on the egg hatching, nymph mortality and moulting success was also analysed. The results show that egg hatching in first‐instar nymphs of T. brasiliensis was lower at extreme RHs and, particularly, it was lowest at 9.3% RH. The survival of starved nymphs was not affected by RH, but the percentage of engorged nymphs and the ecdysis success of these nymphs once fed was diminished strongly by high humidity. Fourth‐instar nymphs preferred to stay at the lowest RH during the first 5 days after feeding and during ecdysis. This preference changed markedly during starvation. Fifteen days after ecdysis, the bugs moved towards intermediate humidities, and 30 days after ecdysis they even preferred the most humid sectors of the gradient. Females preferred to lay eggs in dry environments, suggesting that they may not have a particular hygropreference for oviposition, but that they simply lay their eggs at the RHs where they prefer to stay.