Zombie bugs? Manipulation of kissing bug behavior by the parasite Trypanosoma cruzi

Trypanosoma cruzi infection modulates secreted phospholipase A2 expression in the salivary glands of Rhodnius prolixus

Phospholipases A2 (PLA2) comprise a superfamily of enzymes that specifically catalyze hydrolysis of the ester bond at the sn-2 position of glycerophospholipids, generating lysophospholipids and fatty acids. In Rhodnius prolixus, one of the main vectors of the Chagas's disease etiologic agent Trypanosoma cruzi, it was previously shown that lysophosphatidylcholine, a bioactive lipid, found in the insect's saliva, contributes to the inhibition of platelet aggregation, and increases the production of nitric oxide, an important vasodilator. Due to its role in potentially generating LPC, here we studied the PLA2 present in the salivary glands of R. prolixus. PLA2 activity is approximately 100 times greater in the epithelium than in the contents of salivary glands. Our study reveals the role of the RpPLA2XIIA gene in the insect feeding performance and in the fatty acids composition of phospholipids extracted from the salivary glands. Knockdown of RpPLA2XIIA significantly altered the relative amounts of palmitic, palmitoleic, oleic and linoleic acids. A short-term decrease in the expression of RpPLA2III and RpPLA2XIIA in the salivary glands of R. prolixus was evident on the third day after infection by T. cruzi. Taken together, our results contribute to the understanding of the role of PLA2 in the salivary glands of hematophagous insects and show that the parasite is capable of modulating even tissues that are not colonized by it.

How to repel a killer; chemical identification and effective repellent activity of commercial essential oils against kissing bugs

Triatomines are haematophagous insects, some species are vectors of Trypanosoma cruzi, the aetiological agent of Chagas disease. The main strategy for interrupting T. cruzi transmission is to avoid contact of the vector populations with humans. Volatiles from commercial essential oils are excellent candidates to serve as repellents of kissing bugs. We used an exposure device to assess the repellence effect of eight commercial essential oils on Triatoma pallidipennis. The most effective oils were blended and evaluated against T. infestans, T. pallidipennis and Rhodnius prolixus. The blend was also evaluated on parasitised T. pallidipennis. Data were compared with the commercial repellent NN-diethyl-3-methylbenzamide. We recorded the time the insects spent in the proximity of the host and determined if any of the evaluated oils served as kissing bug repellent. We found commercial essential oils and a blend that significantly reduced the time spent in the proximity of the host. The blend was effective for use by human males and females, repelling infected and non-infected insects. The study of essential oils as repellents of blood-sucking disease-vector insects could shed light on the development of new control strategies.

Interaction of Trypanosoma cruzi, Triatomines and the Microbiota of the Vectors-A Review

This review summarizes the interactions between Trypanosoma cruzi, the etiologic agent of Chagas disease, its vectors, triatomines, and the diverse intestinal microbiota of triatomines, which includes mutualistic symbionts, and highlights open questions. T. cruzi strains show great biological heterogeneity in their development and their interactions. Triatomines differ from other important vectors of diseases in their ontogeny and the enzymes used to digest blood. Many different bacteria colonize the intestinal tract of triatomines, but only Actinomycetales have been identified as mutualistic symbionts. Effects of the vector on T. cruzi are indicated by differences in the ability of T. cruzi to establish in the triatomines and in colonization peculiarities, i.e., proliferation mainly in the posterior midgut and rectum and preferential transformation into infectious metacyclic trypomastigotes in the rectum. In addition, certain forms of T. cruzi develop after feeding and during starvation of triatomines. Negative effects of T. cruzi on the triatomine vectors appear to be particularly evident when the triatomines are stressed and depend on the T. cruzi strain. Effects on the intestinal immunity of the triatomines are induced by ingested blood-stage trypomastigotes of T. cruzi and affect the populations of many non-symbiotic intestinal bacteria, but not all and not the mutualistic symbionts. After the knockdown of antimicrobial peptides, the number of non-symbiotic bacteria increases and the number of T. cruzi decreases. Presumably, in long-term infections, intestinal immunity is suppressed, which supports the growth of specific bacteria, depending on the strain of T. cruzi. These interactions may provide an approach to disrupt T. cruzi transmission.

Lessons to be popular: the chemical basis of aggregation in Trypanosoma cruzi-infected and non-infected Chagasic bugs

Aggregation is one of the most remarkable behaviours in the animal kingdom-a process that is usually governed by pheromones. Triatomines are blood-sucking bugs that act as vectors of Trypanosoma cruzi, the etiological agent of Chagas disease in mammals, including humans. Triatomines usually gather in roosting refuges by using aggregation pheromones of unknown chemical structure. In terms of vector control, one option to reduce triatomine-human contact is via capturing the insects into traps baited with lures based on such aggregation pheromones. As a first step towards this aim, we elucidated the aggregation pheromone in the triatomine Triatoma pallidipennis, using T. cruzi-infected and non-infected bugs. We used different extraction techniques and gas chromatography coupled to mass spectrometry for the identification. Also, two different bioassays were implemented for evaluating the attractant and arrestant activity of the pheromone. We found that T. pallidipennis produced short-chain aldehydes as attractants, and nitrogen-derived compounds as arrestants. We detected differences in the production and perception of these compounds according to whether animals were infected or not. These findings show that T. cruzi may influence triatomine chemical ecology and are promising tools for triatomine control.

Diet of the sylvatic triatomine Mepraia spinolai: Association with Trypanosoma cruzi infection near human settlements

The proximity between infectious disease vector populations and human settlements, and the infection prevalence of vector populations can determine the rate of encounters between vectors and humans and hence infection risk. The diet of sylvatic triatomine vectors (kissing bugs) provides evidence about the host species involved in the maintenance of the protozoan Trypanosoma cruzi, the etiological agent of Chagas disease. Here, we characterized the diet of the Chilean endemic triatomine Mepraia spinolai using Next Generation Sequencing (NGS), and evaluated the relation between T. cruzi infection status and proximity to human settlements, with the proportion of human and human-associated (domestic and synanthropic) vertebrates in the diet. We sampled 28 M. spinolai populations, covering a latitudinal range of ∼800 km in Chile. For each population, genomic DNA was obtained from M. spinolai intestinal content. We assessed T. cruzi infection individually, and sequenced vertebrate cytochrome b to characterize the diet from infected and uninfected pooled samples. Human and human-associated animals were present in the diet of both T. cruzi-infected (13.50 %) and uninfected (10.43 %) kissing bugs. The proportion of human and human-associated vertebrates in the diet of infected M. spinolai was negatively associated with the distance from surrounding human settlements, but no relationship was detected for uninfected kissing bugs. This pattern could be related to alterations of kissing bug feeding behavior when infected by the protozoan. Our results highlight the relevance of developing a deeper knowledge of the wild transmission cycle of T. cruzi, thus advancing in the surveillance of vectors present in the natural environment near human settlements.

Alterations in energy metabolism of Rhodnius prolixus induced by Trypanosoma rangeli infection

Trypanosoma rangeli is a protozoan parasite that infects triatomines and mammals in the Americas, producing mixed infections with Trypanosoma cruzi, the etiological agent of Chagas disease. The former parasite is not pathogenic to humans, but has different levels of pathogenicity, as well as causing physiological and behavioral alterations, to its invertebrate hosts. In this study, we measured locomotory activity, and the glyceride accumulation profile in the hemolymph and fat body, as well as the expression of key genes related to triglyceride metabolism, of Rhodnius prolixus nymphs infected with T. rangeli. We found that the locomotory activity of the insects was correlated with the amount of triglycerides in the fat body. Infected nymphs had increased activity when starved, and also had an accumulation of glycerides in the fat body and hemolymph. These alterations were also associated with a higher expression of the diacylglycerol acyltransferase, lipophorin and lipophorin receptor genes in the fat body. We infer that T. rangeli is able to alter the energetic processes of its invertebrate host, in order to increase the availability of lipids to the parasite, which, in turn modifies the activity levels of the insect. These alterations are discussed with regard to their potential to increase the transmission rate of the parasite.

Opportunistic or selective? Stage-dependent feeding behavior in a wild vector of Chagas disease

The composition and contribution of different host species in the dynamics of vector-borne zoonotic parasites are particularly relevant for public health. Hence, the study of host selection by vectors is fundamental. Developmental stage and infection status are factors that may modulate vector feeding behavior. In the semi-arid Mediterranean ecosystem of South America, the transmission of Trypanosoma cruzi, the protozoan causing Chagas disease, includes the triatomine vector Mepraia spinolai and several vertebrate species. In this field study, we examined whether M. spinolai exhibits an opportunistic feeding behavior dependent upon developmental stage and/or infection status. We found that M. spinolai does not feed according to the relative availability of vertebrate species. In addition, early stage nymphs (first/second instars) fed on twice as many different species as middle (third/fourth instars) and late (fifth instars and adults) M. spinolai, with the former feeding on native rodents and lizards and the latter mostly on rabbits. Infected and uninfected M. spinolai showed similar feeding profiles. Wild triatomine species might be described as stage-dependent selective blood feeders, as a consequence of the temporal and spatial scale at which host-vector interactions occur, highlighting that all developmental stages might be infected and capable of transmitting T. cruzi.

Trypanosoma cruzi Parasite Burdens of Several Triatomine Species in Colombia

Trypanosoma cruzi, the causal agent of Chagas disease, is mainly transmitted by insects of the Triatominae subfamily. In Colombia, there are 26 triatomine species, and 16 of them are naturally infected with the parasite. The parasite loads of naturally infected vectors can be significant in targeting specific species that can affect the epidemiology of the disease. Studying their ecology and behavior is vital to understand their role in T. cruzi transmission dynamics. We evaluated the parasite loads of 182 field-collected triatomines corresponding to 10 species in 13 departments across Colombia. We standardized a methodology to quantify T. cruzi DNA in these insects. We obtained a LOD (limit of detection) of 3.05 p-eq/mL. The 82% of triatomines we evaluated were positive for T. cruzi infection, with loads ranging from hundreds to millions of equivalent parasites per milliliter. Panstrongylus geniculatus, Rhodnius prolixus, and Triatoma dimidiata were the species with the highest loads of T. cruzi; however, other species whose role as vectors is still unknown were also found with high loads of parasites. Our results suggest the relevance of secondary species for T. cruzi transmission in Colombia. We hope our data can help improve entomological surveillance and vector control programs in the country and the region.

Does Trypanosoma cruzi (Chagas, 1909) (Kinetoplastida: Trypanosomatidae) modify the antennal phenotype of Triatoma dimidiata (Latreille, 1811) (Hemiptera: Triatominae)?

Background

Triatoma dimidiata is a vector of the protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease. Phenotypic plasticity allows an organism to adjust its phenotype in response to stimuli or environmental conditions. Understanding the effect of T. cruzi on the phenotypic plasticity of its vectors, known as triatomines, has attracted great interest because of the implications of the parasite–triatomine interactions in the eco-epidemiology and transmission of the etiologic agent of Chagas disease. We investigated if the infection of the vector with T. cruzi may be associated with a change in the antennal phenotype of sylvatic, domestic, and laboratory-reared populations of T. dimidiata.

Methods

The abundance of each type of sensillum (bristles, basiconic, thick- and thin-walled trichoid) on the antennae of T.cruzi-infected and non-infected T.dimidiata reared in the laboratory or collected in sylvatic and domestic ecotopes were measured under light microscopy and compared using Kruskal–Wallis non-parametric tests and permutational multivariate analysis of variance.

Results

We found significant differences between sensilla patterns of infected and non-infected insects within sylvatic and domestic populations. Conversely, we found no significant differences between sensilla patterns of infected and non-infected insects within the laboratory-reared population. Besides, for sylvatic and domestic populations, sexual dimorphism tended to be increased in infected insects.

Conclusion

The differences observed in infected insects could be linked to higher efficiency in the perception of odor molecules related to the search for distant mates and hosts and the flight dispersal in search of new habitats. In addition, these insects could have a positive effect on population dynamics and the transmission of T.cruzi.

Graphical Abstract

The Parasite Load of Trypanosoma cruzi Modulates Feeding and Defecation Patterns of the Chagas Disease Vector Triatoma infestans

Trypanosoma cruzi is the causal agent of Chagas disease, a parasitic zoonosis transmitted mainly through the feces of triatomine insects. Triatoma infestans is the main triatomine vector of this disease in South America. Previous research has shown that T. cruzi infection modifies the behavior of triatomines. We evaluated, for the first time, the effect of parasite load on feeding and defecation behavior, which we quantified by using real-time PCR. The detection time of the host was shorter in infected individuals, and the number of bites increased, while the dejection time was reduced when compared with the non-infected group. A significant correlation between the parasite load and the behavioral changes registered in the infected triatomines was found. These results would indicate that the intensity of T. cruzi infection modulates the feeding and defecation behavior of T. infestans, increasing the vector competence of this triatomine vector.

Body shape and fluctuating asymmetry following different feeding sources and feeding time in a triatomine, Triatoma pallidipennis (Stål, 1892)

Even when an animal has a generalist diet, different food sources can impact its body shape and fluctuating asymmetry (a stress indicator; FA). To test this, we varied the food source (mammalian, avian or defibrinated mammalian blood; and control animals - ad libitum feeding) and the time of feeding (every 8 days, 45 days and ad libitum) having the Chagas triatomine vector, Triatoma pallidipennis (Stål, 1892), as a study animal which has presumable generalist feeding habits. This factorial design was applied since first instar animals until adulthood. As response variables, we measured body shape and FA in adults of both sexes, using a two-dimensional geometric morphometrics protocol. The highest variance in body shape was explained by diet (17%), followed by sex nested within diet (12%). Males had less morphological differentiation than females: females with defibrinated blood provided every 45 days differentiated more, while those that fed on mammalian blood every 8 days differed less. Distances among the averages of the FA component related to shape indicated greater distances between avian blood provided every 45 days and mammalian blood provided every 8 days, as well as between the two groups fed on avian blood (feeding every 8 and 45 days), followed by avian and defibrinated blood, both fed every 8 days. These results indicate that blood source and feeding time have significant effects on the body shape, and FA in females and both sexes. Thus, despite general feeding habits, avian blood showed a greater impact on shape and FA in triatomines. This may select for triatomines to use mammal blood rather than avian blood if they have the chance to do so.

Trypanosoma cruzi Parasite Load Modulates the Circadian Activity Pattern of Triatoma infestans

Simple Summary

We studied the locomotor activity of one of the kissing bug species that transmit the Chagas disease-causing parasite in humans, which usually bites during the night. To date, no other reports researching its behavior take into account the amount of parasites inside the kissing bug; however, some studies have demonstrated that the presence of parasites modifies the activity of some kissing bug species. We recorded their movements in light and dark conditions after part of the insects fed on mammals that had the parasite and others fed on those that did not have the parasite. Later, their amounts of parasites were quantified. We found that, compared with insects with no parasites, kissing bugs with higher parasite amounts increase the number of times they move and the distance they travel, especially during daylight hours. This could imply that the insect increases its time searching for a food source when it is infected with a higher number of parasites, and this could increase the risk of transmission of the parasite to people by the kissing bug.

Abstract

American trypanosomiasis is a disease caused by the flagellate protozoan Trypanosoma cruzi, which is transmitted mainly in endemic areas by blood-sucking triatomine vectors. Triatoma infestans is the most important vector in the southern cone of South America, exhibiting a nocturnal host-seeking behavior. It has been previously documented that the parasite produces changes in some triatomine species, but this is the first time that the behavior of a vector has been evaluated in relation to its parasite load. After comparing the movement events and distance traveled of infected and non-infected T. infestans, we evaluated the change produced by different T. cruzi parasite loads on its circadian locomotor activity. We observed differences between infected and non-infected triatomines, and a significant relation between the parasite load and the increase in locomotor activity of T. infestans, which was accentuated during the photophase. This could have direct implications on the transmission of T. cruzi, as the increased movement and distance traveled could enhance the contact of the vector with the host, while increasing the predation risk for the vector, which could both constitute a risk for vectorial and oral transmission to mammals.

Modification of the Daily Activity Pattern of the Diurnal Triatomine Mepraia spinolai (Hemiptera: Reduviidae) Induced by Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) Infection

Mepraia spinolai, (Porter) 1934, is a diurnal triatomine endemic to Chile and a wild vector of the protozoan Trypanosoma cruzi, (Chagas) 1909, which causes Chagas disease. Behavioral changes in M. spinolai induced by this parasite have been reported previously, which include detection of a potential host, defecation latency, and some life history traits. In this study we assessed changes in locomotor and daily activity due to infection with T. cruzi. No difference was detected in distance traveled between infected and uninfected individuals. However, the groups differed in their daily activity patterns; infected individuals showed significant reduction of movements during the light phase and concentrated their activity in the dark phase. Uninfected individuals showed no differences in locomotor activity between the phases. The results suggest that T. cruzi induces a displacement in the activity of M. spinolai toward the dark phase of the circadian cycle, which may improve its vector competence.

Higher temperatures reduce the number of Trypanosoma cruzi parasites in the vector Triatoma pallidipennis

Background

Relatively little is known about how pathogens transmitted by vector insects are affected by changing temperatures analogous to those occurring in the present global warming scenario. One expectation is that, like their ectothermic vectors, an increase in temperature could reduce their fitness. Here, we have investigated the effect of high temperatures on the abundance of Trypanosoma cruzi parasites during infection in the vector Triatoma pallidipennis.

Methods

We exposed T. pallidipennis nymphs to two strains (Morelos and Chilpancingo) of T. cruzi. Once infected, the fifth-instar bugs were distributed among three different temperature groups, i.e. 20, 30, and 34 °C, and the resulting parasites were counted when the bugs reached adulthood.

Results

The number of parasites increased linearly with time at 20 °C and, to a lesser extent, at 30 °C, especially in the Chilpancingo compared to the Morelos strain. Conversely, at 34 °C, the number of parasites of both strains decreased significantly compared to the other two temperatures.

Conclusions

These results suggest negative effects on the abundance of T. cruzi in T. pallidipennis at high temperatures. This is the first evidence of the effect of high temperatures on a pathogenic agent transmitted by an insect vector in the context of global warming. Further tests should be done to determine whether this pattern occurs with other triatomine species and T. cruzi strains.

Graphical abstract

An Update on the Knowledge of Parasite-Vector Interactions of Chagas Disease

This review focusses on the interactions between the etiologic agent of Chagas disease, Trypanosoma cruzi, and its triatomine vector. The flagellate mainly colonizes the intestinal tract of the insect. The effect of triatomines on trypanosomes is indicated by susceptibility and refractoriness phenomena that vary according to the combination of the strains. Other effects are apparent in the different regions of the gut. In the stomach, the majority of ingested blood trypomastigotes are killed while the remaining transform to round stages. In the small intestine, these develop into epimastigotes, the main replicative stage. In the rectum, the population density is the highest and is where the infectious stage develops, the metacyclic trypomastigote. In all regions of the gut, starvation and feeding of the triatomine affect T. cruzi. In the small intestine and rectum, starvation reduces the population density and more spheromastigotes develop. In the rectum, feeding after short-term starvation induces metacyclogenesis and after long-term starvation the development of specific cells, containing several nuclei, kinetoplasts and flagella. When considering the effects of T. cruzi on triatomines, the flagellate seems to be of low pathogenicity. However, during stressful periods, which are normal in natural populations, effects occur often on the behaviour, eg, in readiness to approach the host, the period of time before defecation, dispersal and aggregation. In nymphs, the duration of the different instars and the mortality rates increase, but this seems to be induced by repeated infections or blood quality by the feeding on infected hosts. Starvation resistance is often reduced by infection. Longevity and reproduction of adults is reduced, but only after infection with some strains of T. cruzi. Only components of the surface coat of blood trypomastigotes induce an immune reaction. However, this seems to act against gut bacteria and favours the development of T. cruzi.

Morphology, Life Cycle, Environmental Factors and Fitness – a Machine Learning Analysis in Kissing Bugs (Hemiptera, Reduviidae, Triatominae)

Populations are permanently evolving and their evolution will influence their survival and reproduction, which will then alter demographic parameters. Several phenotypic, life history and environmental variables are known to be related to fitness measures. The goal of this article was to look into the possible types of those relationships in insects of the subfamily Triatominae, vectors of Trypanosoma cruzi, the causative agent of Chagas disease. After an exhaustive literature review of 7,207 records of publications referring exclusively to all possible features of the triatomines, using 15 keywords those records were reduced to 2,968 publications, that were analyzed individually; after deleting those publications that did not have the data in quantitative form as needed for the objective of this article, I found that 171 papers were adequate for the present analysis. From them I compiled a dataset of 11 variables and 90 cases from 36 triatomine species. Those variables included four environmental, two life cycle, and four morphological variables, and one demographic parameter: a fitness measure (the population intrinsic rate of natural increase, r0), used as dependent variable. However, the relationship between T. cruzi and its vector host was not included in this analysis despite triatomine-T. cruzi interactions constitute an important factor in the evolution of triatomine’s life history. I resorted to the Random Forest method as a machine learning approach for the analysis of this dataset, and found that –in addition to the triatomine species themselves– only the two life cycle variables (mean development time from egg to adult, and mean fecundity, expressed as the average number of female eggs laid per female per day) were statistically significant in determining fitness (r0). The machine learning approach used in the analysis provided a similar but deeper insight into these relationships than classical regression. Except for an analysis on senescence, this is the first study in triatomines addressing these questions. These results will be useful for other theoretical optimization approaches (frequency-dependence, density-dependence, evolutionary game theory, and adaptive dynamics), thus contributing to the theoretical framework for interpreting the succession of stages in insect adaptations, a framework yet to be constructed.

Chagas bugs and trypanosoma cruzi: Puppets and puppeteer?

A widely accepted idea in parasite-host relationships is that the former manipulates the latter so that it increases its own success. In the case of complex life cycles, this means that the parasite is able to manipulate the first host which allows its transmission to the second host. In this paper, I formalize the idea that this may be the case for the Trypanosoma cruzi parasite and its vectors, bugs of the subfamily Triatominae. I discuss the sources of existing evidence and propose some types of manipulation. This manipulation could also occur in the second host, that is, a vertebrate. Here, I emphasize humans and domesticated animals. I also discuss how global change and insecticide resistance may drive the arms race between both, triatomines and T. cruzi, and host manipulation.

Trypanosoma cruzi could affect wild triatomine approaching behaviour to humans by altering vector nutritional status: A field test

Hematophagous insects exhibit complex behaviour when searching for blood-meals, responding to several host stimuli. The hematophagous insect Mepraia spinolai is a wild vector of Trypanosoma cruzi, causative agent of Chagas disease in humans, in the semiarid-Mediterranean ecosystem of Chile. In this study, we evaluated the association between the approaching behaviour to a human host, with T. cruzi infection status and nutritional condition of M. spinolai. To this end, we captured 501 individuals in six consecutive 10 min-timespan, using a human as bait. Captured vectors were weighed, photographed and measured to calculate their nutritional status by means of a Standardized Body Mass Index. Trypanosoma cruzi infection was assessed in the intestinal content by using a real-time PCR assay. Ordinal logistic regressions were performed separately for infected and uninfected groups to evaluate if the nutritional status was associated with the approaching behaviour to a human host, recorded as the time-span of capture. Nutritional status of uninfected triatomines was higher than that from infected ones (p < 0.005). Among the infected, those with higher nutritional status approached first (p < 0.01); there was no effect of nutritional status in the uninfected group. Trypanosoma cruzi infection might affect the foraging behaviour of M. spinolai under natural conditions, probably deteriorating nutritional status and/or altering vector detection abilities.

Vector competence and feeding-excretion behavior of Triatoma rubrovaria (Blanchard, 1843) (Hemiptera: Reduviidae) infected with Trypanosoma cruzi TcVI

Background

Several studies addressed changes on the insect vector behavior due to parasite infection, but little is known for triatomine bugs, vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. We assessed infection rates and metacyclogenesis of T. cruzi (TcVI) in fifth-instar nymphs of Triatoma rubrovaria comparing with the primary vector Triatoma infestans. Also, biological parameters related to feeding-excretion behavior were evaluated aiming to identify which variables are most influenced by T. cruzi infection.

Methodology/principal findings

Fifth-instar nymphs of T. rubrovaria and T. infestans were fed on mice infected with T. cruzi (TcVI). We compared the presence and the number of parasite evolutive forms in excreta of both triatomine species at 30, 60 and 90 days post-infection (dpi) with traditional statistical analyses. Moreover, both species were analyzed through generalized linear models and multinomial logistic regression hypotheses for seven behavioral parameters related to host-seeking and feeding-excretion. Triatoma rubrovaria and T. infestans had similar overall infection and metacyclogenesis rates of T. cruzi TcVI in laboratory conditions. Regarding vector behavior, we confirmed that the triatomine’s tendency is to move away from the bite region after a blood meal, probably to avoid being noticed by the vertebrate host. Interspecific differences were observed on the volume of blood ingested and on the proportion of individuals that excreted after the blood meal, revealing the higher feeding efficiency and dejection rates of T. infestans. The amount of ingested blood and the bite behavior of T. rubrovaria seems to be influenced by TcVI infection. Infected specimens tended to ingest ~25% more blood and to bite more the head of the host. Noteworthy, in two occasions, kleptohematophagy and coprophagy behaviors were also observed in T. rubrovaria.

Conclusions/significance

Laboratory infections revealed similar rate of T. cruzi TcVI trypomatigotes in excreta of T. rubrovaria and T. infestans, one of the most epidemiological important vectors of T. cruzi. Therefore, TcVI DTU was able to complete its life cycle in T. rubrovaria under laboratory conditions, and this infection changed the feeding behavior of T. rubrovaria. Considering these results, T. rubrovaria must be kept under constant entomological surveillance in Rio Grande do Sul, Brazil.

Chagas disease is caused by the etiological agent Trypanosoma cruzi and is mainly transmitted through the excreta of triatomine vectors. It is endemic in Latin America and the Caribbean, affecting ~8 million people. Control programs are based on the elimination of domestic vectors through insecticide-spraying indoors, since there is no vaccine or efficient treatment for chronic patients. However, this strategy is not sustainable where native triatomine species are capable of colonizing peridomestic structures and reinvading human dwellings. Since the ‘virtual’ elimination of Triatomainfestans in Brazil (residual foci remain in Rio Grande do Sul and Bahia), specimens of the native Triatoma rubrovaria have been constantly collected inside human dwellings and peridomiciliary ecotopes in Rio Grande do Sul, southern Brazil, which might represent a real risk for human infections. Here we analyzed a unique and large dataset through classical and modern statistical methods to evaluate T. cruzi infection in T. rubrovaria and to identify host-seeking, and also feeding/excretion behavioral traits that could be influenced by the parasite. Our results indicated that the parasite infection caused changes in T. rubrovaria feeding behavior that could increase T. cruzi TcVI transmission. Moreover, this vector species had similar infection rate to one of the main important Chagas disease vectors in South America, T. infestans. Therefore, T. rubrovaria must be kept under constant entomological surveillance in Rio Grande do Sul, Brazil.

Pathogens Manipulating Tick Behavior-Through a Glass, Darkly

Pathogens can manipulate the phenotypic traits of their hosts and vectors, maximizing their own fitness. Among the phenotypic traits that can be modified, manipulating vector behavior represents one of the most fascinating facets. How pathogens infection affects behavioral traits of key insect vectors has been extensively investigated. Major examples include Plasmodium, Leishmania and Trypanosoma spp. manipulating the behavior of mosquitoes, sand flies and kissing bugs, respectively. However, research on how pathogens can modify tick behavior is patchy. This review focuses on current knowledge about the behavioral changes triggered by Anaplasma, Borrelia, Babesia, Bartonella, Rickettsia and tick-borne encephalitis virus (TBEV) infection in tick vectors, analyzing their potential adaptive significance. As a general trend, being infected by Borrelia and TBEV boosts tick mobility (both questing and walking activity). Borrelia and Anaplasma infection magnifies Ixodes desiccation resistance, triggering physiological changes (Borrelia: higher fat reserves; Anaplasma: synthesis of heat shock proteins). Anaplasma infection also improves cold resistance in infected ticks through synthesis of an antifreeze glycoprotein. Being infected by Anaplasma, Borrelia and Babesia leads to increased tick survival. Borrelia, Babesia and Bartonella infection facilitates blood engorgement. In the last section, current challenges for future studies are outlined.

Behavioral response mediated by feces in Triatoma infestans (Hemiptera: Reduviidae: triatominae) susceptible and resistant to deltamethrin

Chemical cues from feces promote aggregation behavior in Triatoma infestans nymphs and adults. Given the importance of T. infestans resistant to pyrethroids in several areas of Argentina and Bolivia, it would be important to know if there is an association with specific attraction and aggregation behaviors. These behaviors, to and surrounding refuges, play an important role in triatomine population dynamics, an important factor to consider and model for vector control strategies. The aim of the present study was to analyze the behavior of orientation to chemical signals emitted by feces from deltamethrin resistant (R) and susceptible (S) T. infestans. The behavioral assays were performed in a circular glass arena divided in two equal sectors. Fecal signals emitted by both S and R feces are attractants to fifth-instar nymphs of both S and R populations. Both toxicological phenotypes remained significantly longer on R feces, as compared to S feces. This is the first evidence in a triatomine, for the association of an aggregation behavior and insecticide resistance and may be the result of pleiotropic effects surrounding resistance genes.