Seasonal variations in active dispersal of natural populations of Triatoma infestans in rural north-western Argentina

The flight dispersal of Triatoma infestans Klug (Hemiptera: Reduviidae) is one of the main mechanisms determining community re-infestation after control interventions. An empirical model of flight initiation coupled with data from a longitudinal study predicted that the flight dispersal of T. infestans would peak in summer. To test this prediction, longitudinal light trap collections were conducted during 3-8 nights in March (late summer), July (winter) and November (spring) 2003, and in March 2004 in a rural community in north-west Argentina. Following each light-trapping collection date, all peridomestic sites around light traps were inspected to assess the relative abundance and nutritional status of T. infestans at each site. A total of 21 adult and five nymph T. infestans, six Triatoma guasayana Wygodzinsky & Abalos, and nine Triatoma garciabesi Carcavallo et al. were collected in 96 light-trapping nights, whereas 696 T. infestans were collected from the peridomestic sites that surrounded the light traps. The arrival of T. infestans in the light traps occurred in 64% of catch stations and peaked in the summer surveys (10-14 bugs) compared with spring and winter surveys. When winds were < 5 km/h, the arrival of adult T. infestans at the light traps was significantly associated with maximum temperature and relative humidity. This is the first field report of seasonal variations in the flight dispersal activity of T. infestans.     

Effects of chickens on the prevalence of infestation and population density of Triatoma infestans in rural houses of north-west Argentina

Abstract Effects of the presence of chickens on population density of the bug Triatoma infestans , principal vector of Chagas disease, were investigated by standardized sampling (indoors and peridomestically) from sixty-eight houses of three rural communities in north-west Argentina, during March 1992.
The domiciliary density of T. infestans increased linearly with the percentage of bugs that fed on chickens, as identified by agar double-diffusion tests. Bug density was significantly higher in houses where hens usually nested indoors than in those where they did not, as determined by concurrent direct observations and interviews of householders. Multiple linear regression analysis of domiciliary bug density on (a) the total number of people, dogs and cats per house; (b) the percentage of domiciliary bugs that fed on chickens, or (c) the indoor-brooding habit of hens, showed the two variables (b, c) related to chickens as significant predictors in each regression model. Inclusion both variables representing chickens increased the fit significantly. Addition of other potentially confounding factors (domestic insecticide use, type of roof and walls of house) did not affect the significant variables retained in the best-fitting regression model.
Peridomestic infestation was positively associated with the household number of fowls. Chickens were the main bloodmeal source of peridomestic T.infestans populations. Human-fed bugs were detected in peridomestic sites of sixteen houses, indicating active dispersal of adults and large nymphal instars from bedroom areas.
Exclusion of hens from domiciliary areas and promotion of chicken sheds, of an appropriate design that would not harbour bug populations, should limit the triatomine population growth rate and reduce the risk of infestation.     

Infestation of rural houses by Triatoma infestans in the region of Los Llanos (La Rioja, Argentina)

Vectorial transmission of Chagas disease has been strongly reduced in most parts of the Southern Cone countries of South America, except in the Gran Chaco region of Argentina, Bolivia, and Paraguay. Given periodical interruptions of the vector control programmes in the endemic region of the Gran Chaco of Argentina, the vectorial transmission of the disease has been increasing during the last years. From the beginning of 2004, the provincial Ministry of Health of La Rioja, Argentina, started a vector control programme to cover the rural houses of the Los Llanos area in the southwestern area of the Gran Chaco region. This article reports the result of a standardized entomological survey and insecticide application against Chagas disease vectors in the intra and peridomestic structures of the rural houses of Los Llanos. A total of 4062 houses were inspected, of which 46.8% were found to be infested by Triatoma infestans. Infestation by vector species other than T. infestans was less than 0.5%(T. eratyrusiformis and T. platensis). Intradomestic infestation was found in 27.2%, whereas peridomestic infestation was found in 39.3% of the houses. The lowest figure of intradomestic infestation was 6.6% (Department F Varela), and the highest value of intradomestic infestation was 45.1% (Department Independencia). In spite of the demonstrated success of vector control elsewhere, this study shows that the vector populations are susceptible to pyrethroid insecticides in the southern area of the Gran Chaco of Argentina, that there still are regions where rural houses show heavy infestation by T. infestans associated with big peridomestic structures and that the vectorial transmission of the Chagas disease will continue, unless a sustained and well organized vector control effort is installed in the region.     

Comparative study of sensitivity and mortality of Triatoma infestan nymphs III and IV used in the xenodiagnosis of chronic chagasic patients]

Triatoma infestans nymphs have shown a good sensitivity for detecting Trypanosoma cruzi in the blood stream of infected hosts when are used in the xenodiagnosis (XD). This method, with its natural limitations, using seven nymphs III of T. infestans, has been routinely utilized with a satisfactory yield. With the aim of an eventual improving of the yield of XD (with 7 nymphs), two series of 54 XD boxes each, containing a total of 378 nymphs III and 378 nymphs IV respectively, were applied--one of each during three consecutive days--to nine chronic chagasic patients. Each of the nymphs was weighted before and after the application of the boxes, and the intestinal content of them was examined 30, 60 and 90 days later. The main comparative results obtained with nymphs III and IV of T. infestans were: blood ingestion 40 versus 107 mg (2.7 higher), positivity of insects 35.8% versus 50.6% (15.8% higher), positivity of XD boxes (7 nymphs each) 46.3% versus 55.6% (9.3% higher), and mortality rates 28.6% versus 12.2% (16.4% lower). All these results demonstrate that nymphs IV of T. infestans, because their higher capacity of ingesting blood and higher tolerance to examination manipulations, are more suitable for been used in XD.     

Ecogenetics of Triatoma sordida and Triatoma guasayana (Hemiptera: reduviidae) in the Bolivian chaco.

Triatoma guasayana and two putative cryptic species pertaining to T. sordida complex (named groups 1 and 2) occur in sympatry in the Bolivian Chaco. Using multilocus enzyme electrophoresis and subsequent genetic analysis, our work assesses their population distribution and dispersal capacity in domestic, peridomestic, and silvatic environments. Our collections by light trap in the silvatic environment indicated a predominance of T. guasayana and T. sordida group 2 and a lesser abundance of T. sordida group 1 ( pound 10% of the total of captures). Their similar distribution in two silvatic areas 80 km apart supports the hypothesis of their homogeneous dispersal through the Bolivian Chaco. The distribution of T. guasayana and T. sordida groups 1 and 2 was similar between silvatic environment and peridomestic ecotopes where 25% of positive places was occupied by two or three species. Bromeliads were confirmed as favorable shelter for T. guasayana but were free of T. sordida. T. sordida group 1 and to a lesser extent T. guasayana would be more invasive vectors for houses than T. sordida group 2. The spatial partition in the three species sampled in two distant sites suggested a reduced dispersive capacity.     

Distribution and pathogenicity of Trypanosoma cruzi isolated from peridomestic populations of Triatoma infestans and Triatoma guasayana from rural Western Argentina

We assessed the distribution of Trypanosoma cruzi infection in peridomestic triatomines collected manually at a district-wide scale in rural villages around Olta, Western Argentina, and typed the isolated strains according to their pathogenicity to laboratory mice. Of 1623 triatomines examined, only 14 (0.9%) were infected with T. cruzi based on microscopical examination of feces. The prevalence of T. cruzi infection was 0.8% in Triatoma infestans, 2.3% in T. guasayana, and nil in T. garciabesi, T. platensis, and T. eratyrusiformis. Local transmission occurred in kitchens, store-rooms and goat corrals or nearby, though at very low levels. T. cruzi was detected by at least one parasitological method in 11 (79%) of 14 microscope-positive bugs. Hemoculture was the most sensitive method (67%) followed by culture of organ homogenates, histopathology or xenodiagnosis of inoculated suckling mice (55-58%), and culture of microscope-positive bug feces (46%). The evidence suggests that most of the isolated T. cruzi strains would be myotropic type III. Our study establishes for the first time that peridomestic, microscope-positive T. guasayana nymphs were actually infected with T. cruzi, and may be implicated as a putative secondary vector of T. cruzi in domestic or peridomestic sites.     

Spatial pattern of reinfestation by Triatoma infestans in Chancanif, Argentina.

We examined the environmental correlates and the spatial pattern of infestation by Triatoma infestans, a vector of Chagas disease, in a rural area of Argentina five years following an insecticidal campaign. Patterns of infestation were identified in an entomological survey, as mapped with high-resolution satellite imagery and analyzed in a geographic information system. Logistic regression was used to relate infestation to observed household characteristics as well as the location and density of households. Location was the most significant predictor of infestation for domiciles. For peridomestic structures surrounding the domiciles, the combination of location and the presence/absence of goat pens was most significant. In considering any infestation, whether domiciliary or peridomestic, the combination of location, presence/absence of animal pens, and the type of household construction were found to be most significant. Using these statistical relationships to back-classify the field data resulted in accuracies between 85% and 87%. A map of infestation probability for the town of Chancaní was developed from the logistic regression.     

IgM-antibody responses of chickens to salivary antigens of Triatoma infestans as early biomarkers for low-level infestation of triatomines

The recombinant form of a highly immunogenic 14.6 kDa protein in Triatoma infestans saliva (rTiSP14.6) is a potential epidemiological marker for the detection of triatomine bug populations using IgG responses in peridomestic chickens. However, the persistence of the IgG response prevents it being of value for several months in areas where triatomine control programmes have been implemented. In this investigation, IgM-antibody reactions to crude salivary antigens or rTiSP14.6 decayed rapidly after exposure of chickens and were measurable for only 18 days after a single challenge with T. infestans. In serial exposure experiments, chickens from low and high exposure groups showed no significant differences in anti-saliva and anti-rTiSP14.6 IgM-antibody titres. Highly immunogenic salivary antigens of 12 and 14 kDa were recognised by all chicken sera. Sera from peridomestic chickens from sites of known T. infestans infestation in Bolivia also recognised these two antigens and no differences in the IgM responses of sera from chickens from low and high infestation households were detected. IgM responses were specific to infested households and could not be detected in sera from non-infested households. Cross-reactivity studies showed that at least four other triatomine species share the 14.6 kDa salivary antigen. No IgM responses were detected against salivary proteins of mosquitoes and sandflies. Thus, we believe that rTiSP14.6 represents a promising epidemiological marker for the detection of low numbers of triatomines in peridomestic habitats, and the comparison of IgM and IgG responses can be used to detect re-infestation soon after insecticide-based control programmes.     

Ecological characteristics of Triatoma patagonica at the southern limit of its distribution (Chubut, Argentina)

This study aimed at identifying the ecological characteristics of Triatoma patagonica Del Ponte 1929 (Hemiptera: Reduviidae) and evaluating the epidemiological importance of this species at its southernmost distribution limit. We carried out two surveys in the Province of Chubut, in summer and in spring, 1998. In each survey, we interviewed local health care agents for triatomine recognition and reports of the bugs, followed by entomological searches in houses and peridomestic and silvatic biotopes. The presence of T. patagonica was confirmed in two of the five localities indicated by interview. In agreement with previous studies, all these positive localities were east of the 11 degrees C isotherm, within the Monte phytogeographic province. Triatomine abundance and infestation levels (in peridomiciles and peridomestic biotopes) were higher in summer than in spring, possibly reflecting adverse environmental conditions such as flood and cold winter weather. In the silvatic environment, we found three adult bugs under rocks in summer. In peridomestic sites bugs were only found associated with chickens, which were also the only blood meal source identified. Infection by Trypanosoma cruzi was not detected. We conclude that T. patagonica at its southernmost distribution limit does not represent a risk to public health due to its low abundance, lack of association with humans, and absence of T. cruzi infection.     

Longitudinal study, by xenodiagnosis, of parasitemia in patients with chronic Trypanosoma cruzi infection]

A 2-5 years follow-up of parasitemia, by the use of xenodiagnosis (XD) was carried out in nine patients with chronic T. cruzi infection who proceeded from chagasic endemic areas of Chile. The patients (mean age 55 years) were hospitalized in the chronic section of a psychiatry institution sited in a permanent triatomines free urban area. Clinical examination, X-rays images (cardiovascular, esophagus and colon) and electrocardiogram resulted normal in all the patients. Basic study unit of parasitemia was a XD box which contained 7 nymphs III of Triatoma infestans which was used in a serial XD consisting in the simultaneous application of a pair of boxes a day during three consecutive days, making a total of six boxes (42 nymphs). The minimal time of duration of infection (M.D.I.) for each patient was estimated that this was adquired close to hospitalization. The M.D.I. varied between 6 and 45 years. The global positivity of XD boxes ranged between 6.3 and 84.7%, being in three patients lower than 12% and in six patients higher than 52%. In considering the yield of XD it is important to stress that during all the study of the nine patients with chronic chagasic infection 1282 XD boxes were applied resulting positive 582 (45.4%). At the end of the follow-up all patients received specific treatment for chagasic infection with nifurtimox at the daily dose of 10 mg/kg of body weight during 60 days. According to the result, two main conclusions arise: 1.--Serial XD has a high efficiency for detecting, evaluate and evolve parasitemia in patients with chronic chagasic infection. 2.--Parasitemia may present low, medium or high levels in different individuals and has a variable and fluctuating character.     

Usefulness of community participation for the fine temporal monitoring of house infestation by non-domiciliated triatomines

The irregular presence and low abundance of wild triatomines inside domiciles make their detection more difficult than that of domiciled species, so that vector surveillance and evaluation of Chagas disease transmission risk are more challenging. We compared timed manual searches, considered as the gold standard, with community-based collections, for their efficacy at monitoring domestic and peridomestic infestation by non-domiciliated Triatoma dimidiata, and community-based collection was the most sensitive and cost effective. Scaling up community participation permitted investigation of fine temporal variations in infestation by T. dimidiata in over 700 houses. We confirmed a large seasonal infestation during March-July, but weekly and daily collections showed a rather stochastic pattern of bug presence in the houses, even during this period. These data are of key importance for the successful implementation of vector control, and community participation is a method of choice for sustained monitoring of infestation by non-domesticated triatomines.     

Residual effect of a micro-encapsulated formulation of organophosphates and piriproxifen on the mortality of deltamethrin resistant Triatoma infestans populations in rural houses of the Bolivian Chaco region

The Bolivian Chaco is part of the endemic region of Chagas disease and an area where pyrethroid resistant Triatoma infestans (Hemiptera: Reduviidae) populations has been reported. The World Health Organization identified these resistant populations as an important focus for research. The objective of this study was to evaluate the residual effect of a micro-encapsulated formulation containing organophosphate active ingredients and a juvenile hormone analogue (Inesfly 5A IGR) on the mortality of T. infestans. Studies took place in rural houses of the Bolivian Chaco that were treated up to 34 months before and evaluated the susceptibility to pyrethroids of the offspring of field collected insects. Thirty houses were randomly selected within three communities to carry out wall bio-assays with T. infestans nymphs. Mortality was recorded 24, 48 and 72 h after wall contact. Eggs laid by females collected in the area were used to obtain first-instar nymphs and carry out pyrethroid susceptibility tests. The wall bio-assays showed that the micro-encapsulated insecticide eliminates T. infestans populations and produces detectable mortality of insects exposed to walls treated 34 months prior to the tests. The discriminant dose of deltamethrin (0.01 mg/mL) showed 65% nymph survival, whereas at the highest tested dose (1.0 mg/mL) 14% of the nymphs survived. These results show that Inesfly 5A IGR is an appropriate tool for the elimination of intradomestic and peridomestic populations of T. infestans resistant to pyrethroids.     

Vectorial capacity of Triatoma guasayana (Wygodzinsky & Abalos) (Hemiptera: Reduviidae) compared with two other species of epidemic importance

Triatoma guasayana (Wygodzinsky & Abalos) is a peridomestic triatomine with epidemiological importance in Bolivia, that may play an important role in the transmission of Trypanosoma cruzi (Chagas). In this study, two parameters of vectorial capacity were evaluated: the interval of feeding-defecation time and metacyclogenesis, in adult males and females and nymphal instars II to V of T. guasayana with comparisons with Triatoma infestans (Klug) and T. sordida (Stal). The results showed a close relationship between ingestion of blood and beginning of defecation. Values were negative in T. infestans, and T. sordida for instars II, III, IV, and V and also males and females but were positive in female T. sordida. Triatoma guasayana showed only negative values for instar II. Adults and nymphs began defecation as soon as they had finished feeding and required an average of 29.8 min. The analysis of metacyclogenesis showed that T. guasayana was superior to T. infestans and T. sordida. However, the vectorial effectiveness of T. guasayana was significantly affected regarding the percentage of metacyclic trypomastigotes during instars III to V and showed a progressive increase. Females had higher proportions despite their ingestion being half that of T. infestans. The different instars of T. guasayana had a higher parasitic load than those of T. sordida and, although ingestion was 1/3 of that of female T. infestans, there was a progressive increase in metacyclic trypomastigotes in the different nymphal stages of T. guasayana that decreased in adults.     

Factors associated with the occurrence of Triatoma sordida (Hemiptera: Reduviidae) in rural localities of Central-West Brazil

This study estimates the factors of artificial environments (houses and peridomestic areas) associated with Triatoma sordida occurrence. Manual searches for triatomines were performed in 136 domiciliary units (DUs) in two rural localities of Central-West Brazil. For each DU, 32 structural, 23 biotic and 28 management variables were obtained. Multiple logistic regression analysis was performed in order to identify statistically significant variables associated with occurrence of T. sordida in the study areas. A total of 1,057 specimens (99% in peridomiciles, mainly chicken coops) of T. sordida were collected from 63 DUs (infestation: 47%; density: ~8 specimens/DU; crowding: ~17 specimens/infested DU; colonisation: 81%). Only six (0.6%) out of 945 specimens examined were infected with Trypanosoma cruzi. The final adjusted logistic regression model indicated that the probability of T. sordida occurrence was higher in DU with wooden chicken coops, presence of > 30 animals in wooden corrals, presence of wood piles and presence of food storeroom. The results show the persistence of T. sordida in peridomestic habitats in rural localities of Central-West Brazil. However, the observed low intradomestic colonisation and minimal triatomine infection rates indicate that T. sordida has low potential to sustain high rates of T. cruzi transmission to residents of these localities.     

Microsatellite analysis of genetic structure in natural Triatoma infestans (Hemiptera: Reduviidae) populations from Argentina: its implication in assessing the effectiveness of Chagas' disease vector control programmes

The genetic structure in populations of the Chagas' disease vector Triatoma infestans was examined. Comparisons of the levels of genetic variability in populations of this species from areas with different periods since last insecticide treatment and from areas that never received treatment were also carried out. A total of 598 insects from 19 populations were typed for 10 polymorphic microsatellite loci. The average observed and expected heterozygosities ranged from 0.186 to 0.625 and from 0.173 to 0.787, respectively. Genetic drift and limited gene flow appear to have generated a substantial degree of genetic differentiation among the populations of T. infestans. Departures from Hardy-Weinberg expectations due to an excess of homozygotes suggested the presence of null alleles and population subdivision. Microgeographical analysis supports the existence of subdivision in T. infestans populations. Levels of genetic diversity in the majority of the populations of T. infestans from insecticide-treated localities were similar or higher than those detected in populations from areas without treatment. Since the populations of T. infestans are subdivided, a population bottleneck would result in independent genetic drift effects that could randomly preserve different combinations of alleles in each subpopulation. These events followed by a rapid population growth could have preserved high levels of genetic diversity. This study supports the hypothesis of vector population recovery from survivors of the insecticide-treated areas and therefore highlights the value of population genetic analyses in assessing the effectiveness of Chagas' disease vector control programmes.     

Dispersal of Triatoma infestans and other Triatominae species in the arid Chaco of Argentina: flying, walking or passive carriage? The importance of walking females

The aim of this paper was to analyse the active dispersal of Triatoma infestans and the role of chickens as passive carriers of this insect in peridomestic areas of La Rioja, Argentina. To measure active dispersal, monthly catches were made on six consecutive nights for five months (in the warm season) using light traps (for flying insects) and sticky dispersal barriers (for walking insects). The nutritional and reproductive states of adults were evaluated. Over the course of the sampling period, a total of eight flying adults, six walking nymphs and 10 walking adults of the species T. infestans were captured, as well as specimens of Triatoma guasayana, Triatoma eratyrusiformis and Triatoma platensis. Our data demonstrate for the first time that females of T. infestans can disperse by walking. This may be an adaptive strategy because it allows them to move with eggs and/or with good blood reserves, which are not possible when flying. All flying and walking individuals of both genders were of an appropriate physiological state that would allow for colonisation of the target habitat. However, manual inspection of 122 chickens suggests that it is unlikely that these animals passively transport T. infestans. Finally, the dispersal activity of T. infestans was compared with other triatomines using a dispersion index.     

Yielding of xenodiagnosis, according to the number of boxes used in 1,181 persons with chronic chagasic infection diagnosed with indirect hemagglutination reaction]

A study for evaluation of the yielding of xenodiagnosis (XD) in 1,181 persons with a previous positive indirect hemagglutination test (IHAT) for Trypanosoma cruzi infection was carried out. The infection of these people was detected during epidemiological surveys performed in rural-periurban and urban sections of the endemo-enzootic area of Chagas' disease in Chile, which involves the first seven, out of the thirteen political-administrative regions of the country. The sex distribution was 75.0% females and 25.0% males, varying the ages between 2 and 80 years. According to individual and geographical possibilities each person was submitted to 1-8 XD, which consisted in cylindrical wooden boxes containing seven third instar nymphs, laboratory reared, of Triatoma infestans. The boxes, covered with a piece of tulle fixed with a rubber band were applied on the skin of the posterior side of the arm of the subject to be examined, held with a linen bracelet during 25-30 min. After the insects were fed the boxes were maintained in the laboratory at 27 degrees C and 85% relative environmental humidity. Posteriorly, all the nymphs of each box were examined at 30, 60 and 90 days after the application. A drop of abdominal content of each of them, homogenized with a drop of saline, was examined at the microscope looking for T. cruzi. XD resulted positive in 503 (42.6%) people. The positiveness of XD showed a trend of increasing according to the number of boxes used, from 11.4% with one to 51.6% with six. Under a practical point of view, the simultaneous application of four XD boxes seems to be advisable.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of some non-invasive approaches for the detection of red palm weevil infestation

Red palm weevil (RPW) causes severe damage to date palm trees, leading to the death of trees if not detected and treated in time. A major obstacle in RPW control is the difficulty in identifying an early stage infestation In the present study, we measured the efficacy of some non-invasive optical devices including cameras (digital camera and thermal camera), TreeRadarUnit™ (TRU) (Radar 2000, Radar 900), resistograph, magnetic DNA biosensor, and Near-infrared Spectroscopy (NIRS) to detect RPW infestation in date palm trees under field conditions at Riyadh, Saudi Arabia. Date palm trees used in these experiments were selected based on visual observations. After inspection of date palm trees with different devices to detect RPW infestation, each tree was taken down and dissected in detail to validate the accuracy of each device. Results indicated that the visual RPW detection approach presented the highest accuracy (87%) followed by Radar 2000 (77%), Radar 900 (73%), resistograph (73%), thermal camera (61%), and digital camera (52%).Moreover, different stages of RPW placed in plastic cups were fastened onto the healthy date palm trunks to judge RPW presence, the magnetic DNA biosensor correctly detected RPW eggs 75% of the time, followed by detection of larvae (64%) and the control (empty cup) (54%). In another experiment where determinations were made in an open area, the efficiency of the DNA biosensor for detecting adults was 100%, followed by 83%, 63%, 60%, and 39% for pupae, larvae, eggs, and control, respectively. Absorption spectra generated through NIRS for infested, wounded, and control samples of date palm tissue showed a remarkable variation in the gradient of the corresponding peaks between 1850 nm and 1950 nm. Based on the detection efficiency of the tested devices, the resistograph and NIRS have the best potential to detect RPW infestation in date palm trees.     

First report of colonies of sylvatic Triatoma infestans (Hemiptera: Reduviidae) in the Paraguayan Chaco, using a trained dog

In the Gran Chaco region, control of Triatoma infestans has been limited by persistent domestic infestations despite the efforts of the Vector Control Services. In Paraguay, this region is the highest endemic area in the country, showing high levels of indoor and outdoor infestation. Although sylvatic T. infestans have been found in the Bolivian and Argentine Chaco, similar searches for sylvatic populations of this species in Paraguay had been unsuccessful over the last 20 years. Here we present a new approach to detecting sylvatic Triatominae, using a trained dog, which has successfully confirmed sylvatic populations of T. infestans and other triatomine species in Paraguay. A total of 22 specimens corresponding to dark morph forms of T. infestans were collected, and 14 were confirmed as T. infestans by the mitochondrial cytochrome B gene analysis. Through this analysis, one of which were previously reported and a second that was a new haplotype. Triatomines were captured from amongst vegetation such as dry branches and hollows trees of different species such Aspidosperma quebracho-blanco, Bulnesia sarmientoi and Stetsonia coryne. The colonies found have been small and without apparent infection with Trypanosoma cruzi. During the study, Triatoma sordida and Triatoma guasayana have also been found in ecotopes close to those of T. infestans.     

Presence of triatominae (Hemiptera, Reduviidae) and risk of transmission of Chagas disease in Colima, México

With the purpose of evaluating the risk of transmission of the Chagas disease in the State of Colima, México, an entomological survey was performed to obtain triatominae and the rate of infection by Trypanosoma cruzi determined by examination of its dejections. Two hundred eighteen houses located in 16 villages were sampled. In each house the intradomestic and peridomestic habitats were examined by the man-hour-house method, sensor boxes and mouse-baited traps. Also, 12 silvatic places were explored around the same areas using the same techniques as the ones sampled. In total, 456 specimens were captured, of which 139 correspond to Triatoma phyllosoma pallidipennis; 80 to T.p. longipennis; one specimen of T. dimidiata and 236 nymphs of Triatoma sp. Two hundred ninety seven insects were captured in the intradomestic habitat, 132 in the peridomestic and 26 in the silvatic. The index of positive houses was 27%, located in the central area of the state. The rate of natural infection with T. cruzi showed 25.6%. This results confirmed the presence of two important vectors of the Chagas disease in Colima. Its preference for the domestic habitat and its high levels of natural infection with T. cruzi suggested the existence of a significant risk for its transmission in this area of the country.