State-dependency of host-seeking in Rhodnius prolixus: The post-ecdysis time

The source of blood of most haematophagous insects plays at the same time the double role of host and potential predator. Feeding behaviour should be triggered only when necessary and should be completed as quickly as possible. From an epidemiological point of view, this modulation has an impact on the feeding frequency of disease vectors and, as a consequence, on the transmission of parasites. At present, not many data are available on the influence of the physiological state on the motivation to feed, and mostly limited to a few mosquito species. We analyzed the host-seeking behaviour of Rhodnius prolixus as a function of the time elapsed since the ecdysis, by testing the response of larvae to a blood source, and long- (CO₂) and short-range (heat) orientation cues associated to their vertebrate hosts. Our experiments demonstrated that during the first days following the ecdysis insects do not respond to any stimuli. The ability to follow chemical and physical cues increases either gradually (heat) or step-wise (CO₂) with post-ecdysis time. A few insects started to feed on day 2, but only at day 7 following the ecdysis 50% of them took a blood meal, to reach the highest motivation to feed on day 10. The reasons for the “maturation period” in feeding behaviour of R. prolixus are discussed.     

Circadian system responses to nocturnal and diurnal hosts in the kissing bug,Triatoma infestans

ABSTRACT

Insects express diverse behavioral rhythms synchronized to environmental cycles. While circadian entrainment to light–dark cycles is ubiquitous in living organisms, synchronization to non-photic cycles may be critical for hematophagous bugs that depend on rhythmic hosts. The purpose was to determine whether Triatoma infestans are capable of synchronizing to the circadian rhythms of potential hosts with temporally distinct activity patterns; and, if so, if this synchronization occurs through masking or entrainment. Precise synchronization with the food source may be critical for the insects’ survival due to the specific predatory or defensive nature of each host. Kissing bugs were housed in a compartment in constant dark, air-flow-connected to another compartment with a nocturnal or a diurnal host; both hosts were synchronized to a light–dark cycle. The activity rhythms of kissing bugs were modulated by the daily activity rhythms of the vertebrates. Effects were a decrease in the endogenous circadian period, independent of the host being nocturnal or diurnal; in some cases relative coordination occurred and in others synchronization was clearly achieved. Moreover, splitting and bimodality arose, phenomena that were also affected by the host presence. The results indicate that T. infestans were able to detect the non-photic cycle of their potential hosts, an ability that surely facilitates feeding and hinders predation risk. Understanding triatomines behavior is of fundamental importance to the design of population control methods.     

La première observation in natura de l’entomophagie de Panstrongylus geniculatus (Latreille 1811) hématophage vecteur de la maladie de Chagas (Hemiptera: Reduviidae)

Le comportement entomophage de Panstrongylus geniculatus (Latreille 1811), vecteur de la maladie de Chagas, est observé pour la première fois dans la nature, sur un Lépidoptère (Eacles sp., Lepidoptera: Saturniidae) au cours d’une chasse à la lumière dans une forêt de Guyane française.     

Chronobiological basis of thermopreference in the haematophagous bug Triatoma infestans

The chronobiological basis of the daily dynamics of thermopreference was tested in adults of Triatoma infestans, continuously registering the preferred temperature of insects released over a temperature gradient for 13 days. We found that the thermopreference in T. infestans is a dynamic process that depends on the time of the day and the post-feeding time. When submitted to a 12:12 h light/darkness cycle (L/D), the preferred temperature reached the highest and the lowest values at the end of the light and dark phases, respectively. This daily rhythm persisted under constant conditions of illumination (D/D and L/L), suggesting the existence of an internal oscillator controlling this behaviour. Statistical analysis revealed that the thermopreference of insects kept under L/D exhibited a ca. 24 h periodicity, while insects kept in D/D and L/L showed free-running periods of tau((D/D))=23.35 and tau((L/L))=27.35 h, respectively. The persistence of a cyclic pattern of thermopreference under constant conditions, and free-running periods, close to, but different from 24 h, demonstrate the existence of an endogenous control of the thermopreference in this species. The biological relevance of these results is discussed in the light of the hypothesis that both the length of time elapsed since feeding and the time of the day modify thermopreference in these bugs. The gradual decline in preferred temperature following feeding may be associated with energy conservation during starvation. The rhythmic modulation of thermopreference may be associated with the daily rhythm of locomotion activity shown by these bugs.     

Atlas of Mexican Triatominae (Reduviidae: Hemiptera) and vector transmission of Chagas disease

Chagas disease is one of the most important yet neglected parasitic diseases in Mexico and is transmitted by Triatominae. Nineteen of the 31 Mexican triatomine species have been consistently found to invade human houses and all have been found to be naturally infected with Trypanosoma cruzi. The present paper aims to produce a state-of-knowledge atlas of Mexican triatomines and analyse their geographic associations with T. cruzi, human demographics and landscape modification. Ecological niche models (ENMs) were constructed for the 19 species with more than 10 records in North America, as well as for T. cruzi. The 2010 Mexican national census and the 2007 National Forestry Inventory were used to analyse overlap patterns with ENMs. Niche breadth was greatest in species from the semiarid Nearctic Region, whereas species richness was associated with topographic heterogeneity in the Neotropical Region, particularly along the Pacific Coast. Three species, Triatoma longipennis, Triatoma mexicana and Triatoma barberi, overlapped with the greatest numbers of human communities, but these communities had the lowest rural/urban population ratios. Triatomine vectors have urbanised in most regions, demonstrating a high tolerance to human-modified habitats and broadened historical ranges, exposing more than 88% of the Mexican population and leaving few areas in Mexico without the potential for T. cruzi transmission.     

Cytogenetic Analysis of Experimental Hybrids in Species of Triatominae (Hemiptera-Reduviidae)

A cytogenetic analysis was performed in experimental hybrids between species of Chagas disease transmitting bugs with remarkable differences in the amount and distribution of heterochromatin. Using C-banding technique, we identified the parental species chromosomes and analysed the meiotic behaviour in the male hybrids between Triatoma platensis and T. infestans, T. platensis and T. delpontei, and T. infestans and T. rubrovaria. The two former hybrids have an entirely normal meiotic behaviour despite the extensive differences in C-banded karyotypes observed in the parental species, indicating that heterochromatin differences between homeologous chromosomes are not a barrier that influences meiotic synapsis and recombination. On the contrary, the experimental hybrids between T. infestans and T. rubrovaria show failures in pairing of homeologous chromosomes that lead to the production of abnormal spermatids and hybrid sterility. Our data suggest that karyotypic repatterning within triatomines has involved at least two different pathways. Among closely related species, chromosomal changes have largely involved addition or deletion of heterochromatic regions. In more distant species, chromosomal rearrangements (i.e. inversions and translocations) have also arisen. Hybridisation data also allow to hypothesize about the origin and divergence of this taxonomic group, as well as the mechanisms that maintain species isolation.     

Trypanosoma cruzi (Kinetoplastida Trypanosomatidae): ecology of the transmission cycle in the wild environment of the Andean valley of Cochabamba, Bolivia

An active Trypanosoma cruzi transmission cycle maintained by wild rodents in the Andean valleys of Cochabamba Bolivia is described. Wild and domestic Triatoma infestans with 60% infection with T. cruzi were found and was evidenced in 47.5% (rodents) and 26.7% (marsupial) by parasitological and/or serologycal methods. Phyllotis ocilae and the marsupial species Thylamys elegans, are the most important reservoirs followed by Bolomys lactens and Akodon boliviensis. In spite of both genotypes (TCI and TCII) being prevalent in Bolivia, in our study area only T. cruzi I is being transmitted. Our data suggest that wild T. infestans and wild small mammals play an important role in the maintenance of the transmission cycle of T. cruzi. Furthermore, the finding of high prevalence of T. cruzi infection in wild T. infestans point to the risk of the dispersion of Chagas' disease.     

Impact of climate change on vector transmission of Trypanosoma cruzi (Chagas, 1909) in North America

Climate change can influence the geographical range of the ecological niche of pathogens by altering biotic interactions with vectors and reservoirs. The distributions of 20 epidemiologically important triatomine species in North America were modelled, comparing the genetic algorithm for rule‐set prediction (GARP) and maximum entropy (MaxEnt), with or without topographical variables. Potential shifts in transmission niche for Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) (Chagas, 1909) were analysed for 2050 and 2070 in Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. There were no significant quantitative range differences between the GARP and MaxEnt models, but GARP models best represented known distributions for most species [partial‐receiver operating characteristic (ROC) > 1]; elevation was an important variable contributing to the ecological niche model (ENM). There was little difference between niche breadth projections for RCP 4.5 and RCP 8.5; the majority of species shifted significantly in both periods. Those species with the greatest current distribution range are expected to have the greatest shifts. Positional changes in the centroid, although reduced for most species, were associated with latitude. A significant increase or decrease in mean niche elevation is expected principally for Neotropical 1 species. The impact of climate change will be specific to each species, its biogeographical region and its latitude. North American triatomines with the greatest current distribution ranges (Nearctic 2 and Nearctic/Neotropical) will have the greatest future distribution shifts. Significant shifts (increases or decreases) in mean elevation over time are projected principally for the Neotropical species with the broadest current distributions. Changes in the vector exposure threat to the human population were significant for both future periods, with a 1.48% increase for urban populations and a 1.76% increase for rural populations in 2050.     

Behavioural and electrophysiological responses of Triatoma dimidiata nymphs to conspecific faecal volatiles

The behavioural and electrophysiological (electroantennography) responses of the first two instars of Triatoma dimidiata (Hemiptera: Reduviidae) Latreille to fresh and dry faecal headspace volatile extracts from fifth instar conspecific nymphs and synthetic compounds were analysed in this study. Recently emerged nymphs (3–5 days) aggregated around filter paper impregnated with dry faeces and around filter paper impregnated with extracts from both fresh and dry faeces. Older first instars (10–15 days) and second instars aggregated around filter paper impregnated with fresh and dry faeces, and their respective headspace extracts. Dry faecal volatile extracts elicited the strongest antennal responses, followed by fresh faecal extracts. Gas chromatography?mass spectrometry analysis of dried faecal headspace volatiles demonstrated the presence of 12 compounds: 2‐ethyl‐1‐hexanol, 1,2,4‐trimethylbenzene, n ‐octadecane, n ‐nonadecane, n ‐eicosane, n ‐heneicosane, n ‐tricosane, n ‐pentaeicosane, n ‐hexaeicosane, n ‐octaeicosane, nonanal, and 4‐methyl quinazoline. In fresh faecal headspace extracts, only nonanal was clearly detected, although there were other trace compounds, including several unidentified sesquiterpenes. Four of the 11 compounds tested individually elicited aggregation behaviour at concentrations of 100 ng/µL and 1 µg/µL. A blend containing these four components also mediated the aggregation of nymphs. These volatiles may be valuable for developing monitoring methods and designing sensitive strategies to detect and measure T. dimidiata infestation.     

Niche invasion,competition and coexistence amongst wild and domestic Bolivian populations of Chagas vector Triatoma infestans (Hemiptera,Reduviidae, Triatominae)

The model developed for human parasites by Bottomley et al. (2007) [52] has been adapted to the dynamics of triatomines to better understand the processes of niche invasion, competition among species and coexistence. In Bolivia, both wild and domestic populations of Triatoma infestans exist. Their ecological niches are normally separated and the two populations do not interbreed, behaving as two distinct species. However, it has been suggested that the two populations may compete, highlighting therefore the potential risk of wild populations invading human dwellings. The model revealed the importance of the basic reproduction rates R₀ of triatomine colonies for the risk of invasion. This depends not only on life traits such as survival and fecundity, but also on (1) the density-dependence phenomenon that limits triatomine establishment, (2) on house exposure to infection and (3) on the correlation between house susceptibility to domestic T. infestans and house susceptibility to wild T. infestans. Competition and coexistence amongst the two groups of T. infestans may occur under particular conditions, but are very unlikely.