Haematophagy and cleptohaematophagy of Clerada apicicornis (Hemiptera: Lygaeidae), a potential biological control agent of Rhodnius prolixus (Hemiptera: Reduviidae)

Because of its ability to prey on Triatominae in rural houses, Clerada apicicornis has been suggested as a potential biological control agent of Rhodnius prolixus. It has also been suggested as a potential vector of mammalian trypanosomes such as Trypanosoma cruzi, because of its ability to take blood directly from mammals. To help resolve these conflicting ideas, we assessed the haematophagic behaviour of C. apicicornis by carrying out feeding trials on laboratory animals. Cleptohaematophagic behaviour was also assessed by allowing C. apicicornis to feed on R. prolixus previously engorged with avian blood. The low proportion of blood meals taken directly from laboratory animals indicates a facultative haematophagy in this species, whereas a greater proportion of nymphs and adults were able to obtain vertebrate blood by predation on engorged R. prolixus. The results suggest that C. apicicornis is unlikely to be effective as a biological control agent, but is also unlikely to have a significant role in the transmission of vertebrate pathogens.

Comparison of polymerase chain reaction on fresh tissue samples and fecal drops on filter paper for detection of Trypanosoma cruzi in Rhodnius prolixus

PCR detection of Trypanosoma cruzi in Rhodnius prolixus using fresh tissue or fecal drops on filter paper showed comparable results: 38.7% infection rate using the fresh tissue sample and 37.9% by dried fecal drop.

Rhodnius robustus in Bolivia identified by its wings

Wings of a Rhodnius specimen from Alto Beni (Bolivia) was examined for identification and compared with R. stali, R. robustus, (certified Bolivian species), R. pictipes and R. prolixus (suspected Bolivian species). A projection of the unidentified wings as supplementary data into a discriminant analysis of shape revealed clear cut differences with R. stali and R. pictipes, less differences with R. prolixus, and none with R. robustus. Combining global size and shape of the wings, the unknown specimen was identified as R. robustus. Thus, this study confirmed the presence of R. robustus in Bolivia. It also highlighted the possibility of morphometrics to taxonomically interpret one individual, or even one piece of an individual, when related species data are available for comparison.

Differentiation and genetic analysis of Rhodnius prolixus and Rhodnius colombiensis by rDNA and RAPD amplification

Domiciliated Rhodnius prolixus and sylvatic R. colombiensis were analyzed in order to confirm their genetic divergence and verify the risk that the latter represents in the domiciliation process, and to provide tools for identifying the sources of possible reinfestation by triatomines in human dwellings allowing control programs to be undertaken. Comparison of random amplified polymorphic DNA amplification patterns and cluster analysis suggests reproductive discontinuity between the two species. The calculated statistical F value of 0.24 and effective migration rate of 0.6 individuals per generation are insufficient to maintain genetic homogeneity between them and confirm the absence of present genetic flow. R. colombiensis presents higher intrapopulation variability. Polymerase chain reaction of ribosomal DNA supports these findings. The low genetic flow between the two species implies that R. colombiensis do not represent an epidemiological risk for the domiciliary transmission of Trypanosoma cruzi in the Tolima Department. The lower variability of the domiciliated R. prolixus could result in greater susceptibility to the use of pesticides in control programs.

Rhodnius amazonicus Almeida, Santos & Sposina, 1973, Bona Species, Close to R. pictipes Stål, 1872 (Heteroptera, Reduviidae, Triatominae)

The discovery of two atypical specimens of Rhodnius pictipes Stål, 1872 in French Guiana and the examination of the female holotype of R. amazonicus Almeida, Santos & Sposina, 1973, the only specimen of this species so far known, lead us to propose the rehabilitation of R. amazonicus synonymized with R. pictipes. The male is described for the first time and the female redescribed. Both external characters and genitalia distinguish R. amazonicus from R. pictipes. R. amazonicus shows affinities not only with pictipes but also with R. stali Lent, Jurberg & Galvão, 1993 and R. paraensis Sherlock, Guitton & Miles, 1977. A key is provided for these four species forming, in all likelihood, a natural group, i.e. the "pictipes group".

The Triatomines of Northern Peru, with Emphasis on the Ecology and Infection by Trypanosomes of Rhodnius ecuadoriensis (Triatominae)

Information on the distribution and synanthropic behaviour of triatomines is essential for Chagas disease vector control. This work summarises such information from northern Peru, and presents new data on Rhodnius ecuadoriensis - an important local vector infesting 10-35% of dwellings in some zones. Three species are strongly synanthropic and may be suitable targets for chemical control of domestic/peridomestic bug populations. Panstrongylus herreri, the main domestic vector in the area, is probably present in sylvatic ecotopes in the Marañón river system. R. ecuadoriensis and Triatoma dimidiata seem exclusively domestic; biogeographical and ecological data suggest they might have spread in association with humans in northern Peru. Confirmation of this hypothesis would result in a local eradication strategy being recommended. Presence of trypanosome natural infection was assessed in 257 R. ecuadoriensis; Trypanosoma rangeli was detected in 4% of bugs. Six further triatomine species are potential disease vectors in the region (T. carrioni, P. chinai, P. rufotuberculatus, P. geniculatus, R. pictipes, and R. robustus), whilst Eratyrus mucronatus, E. cuspidatus, Cavernicola pilosa, Hermanlentia matsunoi, and Belminus peruvianus have little or no epidemiological significance. A strong community-based entomological surveillance system and collaboration with Ecuadorian public health authorities and researchers are recommended.

Observations on the Domestic Ecology of Rhodnius ecuadoriensis (Triatominae)

Rhodnius ecuadoriensis infests peridomiciles and colonises houses in rural southern Ecuador. Six out of 84 dwellings (7%) surveyed in a rural village were infested (78 bugs/infested domicile; 279 bugs were collected in a single dwelling). Precipitin tests revealed R. ecuadoriensis fed on birds (65%), rodents (31%), marsupials (8%), and humans (15%) - mixed bloodmeals detected in 37.5% of individual samples. Trypanosoma cruzi from opossums and rodents may thus be introduced into the domestic cycle. Wasp parasitoidism was detected in 6.5% of 995 R. ecuadoriensis eggs (only in peridomestic habitats). Control strategies should integrate insecticide spraying (indoors and peridomestic), better management of poultry, and housing improvements. A possible inefficacy of Malathion is reported.

Activity and Residual Effect of Two Formulations of Lambdacyhalothrin Sprayed on Palm Leaves to Rhodnius prolixus

The insecticidal activity and residual effect of two formulations of lambdacyhalothrin were evaluated with Rhodnius prolixus;laboratory and field tests were conducted in the State of Chiapas, Mexico. The results indicate that the lethal concentrations of the active ingredient of SC (LC50 = 2.37 and LC90 = 8.5 mg, a.i./m²) were 4-8 times than those with the insecticide WP applied on R. prolixus bugs in palm leaves, a common building material for thatched roofs. Other investigators in South America recommended applying 30 mg a.i./m² in porous materials; we obtained that the products WP and SC were 3.5 and 16 times more effective on palm leaves. Regarding the evaluation of the residual effects in field spraying, there was up to 15 months persistence after the application of WP in two doses (8.6 mg a.i./m² and 3.752 mg a.i./m²) with SC. We consider R. prolixus highly susceptible to the employed pyrethroids; they could be used to control this vector in the state of Chiapas, Mexico.

Aggregation Behaviour and Interspecific Responses in Rhodnius prolixus Stål

The response to intra- and interspecific faecal assembling signals was tested in Rhodnius prolixus. Papers impregnated with excrement of R. prolixus induced the aggregation of larvae of this species, but also of those of Triatoma infestans. However, faeces belonging to T. infestans were not able to assemble larvae of R. prolixus. On the other hand, there was no response of R. prolixus to putative chemical factors from their cuticle (footprints), in contrast to T. infestans. Results are discussed as related to the ecology of both species.

Impact of residual spraying on Rhodnius prolixus and Triatoma dimidiata in the department of Zacapa in Guatemala

As a vector control program to control Chagas disease in Guatemala, residual spraying of Rhodnius prolixus and Triatoma dimidiata was performed, and its impact was measured in the department of Zacapa. In order to identify infested villages and determine the degree of infestation, a baseline entomological survey to identify municipalities infested with vectors followed by an additional vector survey in areas known to be infested was conducted. Residual spraying using pyrethroid insecticides was performed at all the villages identified as being infested with the vectors. The residual spraying was shown to be highly effective against both vectors by the decrease in infestation indices after spraying. Analysis of the cost-effectiveness of the spraying showed that the average cost of insecticides per house is high when compared with that in Southern Cone countries.

Epidemiology of Chagas disease in Guatemala: infection rate of Triatoma dimidiata, Triatoma nitida and Rhodnius prolixus (Hemiptera, Reduviidae) with Trypanosoma cruzi and Trypanosoma rangeli (Kinetoplastida, Trypanosomatidae)

A five-year domiciliary collection in the 22 departments of Guatemala showed that out of 4,128 triatomines collected, 1,675 were Triatoma dimidiata (Latreille, 1811), 2,344 were Rhodnius prolixus Stal 1859, and only 109 were T. nitida Usinger 1939. The Chagas disease parasite, Trypanosoma cruzi, was found in all three species. Their natural infection rates were similar in the first two species (20.6%; 19.1%) and slightly lower in T. nitida(13.8%). However there was no significant difference in the infection rates in the three species (p = 0.131). T. dimidiata males have higher infection rates than females (p = 0.030), whereas for R. prolixus there is no difference in infection rates between males and females (p = 0.114). The sex ratios for all three species were significantly skewed. More males than females were found inside houses for T. dimidiata (p < 0.0001) and T. nitida (p = 0.011); a different pattern was seen for R. prolixus (p = 0.037) where more females were found. Sex ratio is proposed as an index to show the mobility of T. dimidiata in different populations. T. dimidiata is widely distributed in the country, and is also the main vector in at least ten departments, but R. prolixus with higher vectorial capacity is an important vector in at least two departments.

Redescription of Nyssomyia intermedia (Lutz & Neiva, 1912) and Nyssomyia neivai (Pinto, 1926) (Diptera: Psychodidae)

The phlebotomine sand flies Nyssomyia intermedia and Nyssomyia neivai are the probable vectors of American tegumentary leishmaniasis in the Southern and Southeastern regions of Brazil. These species form a complex, being difficult to separate between either females or males of the two members based on recognized morphological characteristics. Both N. intermedia and N. neivai are redescribed here in the search for characters that facilitate their correct identification. It was possible to differentiate females by means of spermathecal characteristics. Males could be separated with confidence by the tips of the genital filaments, which have the form of a deep spoon, the angle of the concavity being well accentuated in N. intermedia and much shallower in N. neivai.

Changes associated with laboratory rearing in antennal sensilla patterns of Triatoma infestans, Rhodnius prolixus, and Rhodnius pallescens (Hemiptera, Reduviidae, Triatominae)

We examined changes in the array of antennal sensilla of three species of Triatominae (Triatoma infestans, Rhodnius prolixus, and R. pallescens) following their establishment for different periods in laboratory culture. In each case, the laboratory colonies were compared with conspecific samples taken directly from the field, by quantitative analysis of the sensilla arrays on the three distal segments of the antenna in terms of the densities of three types of chemoreceptors (basiconics and thick and thin walled trichoids) and one type of mechanoreceptor (bristles). Sensilla densities were compared by ANOVA or non-parametric tests, and by multivariate discriminant analysis. Strains of the same species reared in different laboratories showed significant differences in their sensilla arrays, especially when compared to field-collected material from the same geographic origin. A Bolivian strain of T. infestans reared in the laboratory for 15 years and fed at monthly intervals, showed greatest differences from its conspecific wild forms, especially in terms of reductions in the number of chemoreceptors. By contrast, an Argentine strain of T. infestans reared for 25 years in the laboratory and fed weekly, showed a relative increase in the density of mechanoreceptors. A Colombian strain of R. prolixus reared for 20 years and fed weekly or fortnightly, showed only modest differences in the sensilla array when compared to its wild populations from the same area. However, a Colombian strain of R. pallescens reared for 12 years and fed fortnightly, did show highly significant reductions in one form of chemoreceptor compared to its conspecific wild populations. For all populations, multivariate analysis clearly discriminated between laboratory and field collected specimens, suggesting that artificial rearing can lead to modifications in the sensory array. This not only supports the idea of morphological plasticity in these species, but also suggests caution in the use of long-established laboratory material for experimental studies designed to extrapolate the natural behaviour and physiology of these species.