Biological cycle and preliminary data on vectorial competence of Triatoma boliviana in laboratory conditions

Behavioral parameters of six populations of Meccus phyllosomus longipennis (Heteroptera: Reduviidae) from areas with high and low prevalences of Trypanosoma cruzi human infection

Three behaviors of epidemiological importance, namely feeding latency, feeding duration and defecation latency, for six populations of Meccus phyllosomus longipennis (Usinger) from areas of central, western and north-central Mexico with high (HP) and low (LP) prevalence of Trypanosoma cruzi (Chagas) human infection were evaluated in this study. The median feeding latency (the time taken to begin feeding) was highly variable between instars. Within-instar comparisons showed that at least 65% of the LP populations (N3 to adult) started to feed significantly (P < 0.05) later than the HP population, with N1 showing no difference, and N2 from LP populations feeding sooner than those from HP populations. The six populations had similar median feeding durations within instars. A higher (P < 0.05) percentage of the instars from HP populations defecated faster than the respective instars from the three LP populations. Approximately 25% of the young nymphs (N1 to N3) and females in the HP populations defecated < 2 min postfeeding, compared with 4%-6% of the young nymphs and 1.3%-3% of females in the LP populations. Moreover, 17.7%-38.8% of the older nymphs (N4 to N5) in the HP populations and 6.8%-13.4% in the LP populations defecated during or immediately after feeding. Our results indicate that the HP populations have a greater potential than the LP populations to transmit T. cruzi infections, which may underlie the differences in the prevalence of T. cruzi infection in some areas where M. p. longipennis is currently distributed.

Dynamics of feeding and defecation behavior of Triatoma infestans hybrids

Triatoma platensis is occasionally found coexisting with Triatoma infestans in chicken coops in Argentina. Some authors have reported the presence of hybrid specimens of both species in chicken coops and other peridomestic habitats. Given the coexistence of T. infestans with T. platensis and the possibility of generating fertile hybrids, it is important to evaluate the vectorial competence of these hybrids. The objective of this study was to record the dynamics of feeding-defecation behavior in fifth-stage nymphs and adults of hybrids between both species and to compare it with T. platensis and T. infestans. Three experimental groups were formed separated by stage and sex: Hybrid group, T. infestans group, and T. platensis group. During feeding, the following variables were recorded for each group: (i) blood meal size, (ii) feeding time, (iii) number of defecations during feeding, and (iv) number of defecations at 10 and 30 min after feeding. The results indicate that adults and fifth-instar nymphs of hybrids have a feeding and defecation behavior similar to T. infestans: they achieve feeding in a short time and first defecation occurs during or just after feeding. Nevertheless, hybrid's ingestion of blood occurs at higher velocity and they require higher blood intake to provoke early defecations. Considering the blood ingestion velocity, the amount of blood ingested, and the short time required for the production of the first defecation, the results of this study suggest that hybrid can be a competent Trypanosoma cruzi vector.

Life Cycle, Feeding, and Defecation Patterns of Triatoma carrioni (Hemiptera: Reduviidae), Under Laboratory Conditions

Chagas disease is caused by Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae). It is transmitted to humans primarily through contaminated feces of blood-sucking vectors of the subfamily Triatominae, known in Ecuador as 'chinchorros'. Some Triatominae species can adapt to domiciliary and peridomiciliary environments where T. cruzi can be transmitted to humans. Triatoma carrioni (Larrousse 1926) colonizes domestic and peridomestic habitats up to 2,242 m above sea level (masl) in southern Ecuador (Loja Province) and northern Peru. This study describes the life cycle, feeding, and defecation patterns of T. carrioni under controlled laboratory conditions using mice as hosts. Specimens were collected in Loja Province, Ecuador, and maintained in the laboratory. The life cycle was approximately 385.7 ± 110.6 d. There was a high mortality rate, 40.9% for first instars and 38.9% for fifth instars (NV). Feeding and defecation patterns for each life stage were examined by recording: insertion time of the proboscis into the host, total feeding time, time to first defecation, and weight of the bloodmeal. Total feeding time varied between 20.6 ± 11.4 min for first instars (NI) and 48.9 ± 19.0 min for adult females. The time to first defecation was variable but ranged from 9.8 ± 10.6 min for NI to 39.4 ± 24.7 min for NV during feeding. This suggests that T. carrioni has an annual life cycle and is a potential vector of T. cruzi in Loja Province. Improved knowledge of populations of T. carrioni in domestic and peridomestic environments of Ecuador can have a significant impact on the prevention and control of Chagas disease.

Life history of two abundant populations of Dipetalogaster maximus (Uhler, 1894) (Hemiptera: Reduviidae: Triatominae) in northwestern Mexico

We focused on the analysis of biological parameters of two different abundant populations of Dipetalogaster maximus (Uhler) (Hemiptera: Reduviidae: Triatominae) from northwestern Mexico. The biological parameters were related to hatching of eggs, life cycle, and meal needed for molting by each instar of two populations from environmentally similar areas (El Fandango and San Dionisio) with a similar number of available hosts as blood meal sources. The D. maximus populations from the two locations were evaluated and compared. No significant differences (P>0.05) were recorded for the average hatching time of the two cohorts. The median egg-to-adult development time and the number of blood meals at each nymphal group were significantly shorter (P<0.05) for the El Fandango cohort. The number of obtained females at the end of the cycles, number of eggs laid, and rate of egg hatching were significantly higher (P<0.05) for the El Fandango cohort. These results contribute to the estimation of abundances of the studied populations of D. maximus in areas where many tourists go for camping and have an increased risk of being bitten and infected by this species.

Biology of the introduced species Triatoma lecticularia (Hemiptera: Reduviidae) to northwestern Mexico, under laboratory conditions

The first record of Triatoma lecticularia out of its reported distribution area together with the brief description of the said area is provided in this paper. In addition, some biological parameters related to hatching of eggs, life cycle and feeding and defecation behaviors for each instar of one population of T. lecticularia from its previously reported distribution area (PR) and for each instar of that introduced recently found population (IS) of this species were evaluated and compared. Twenty-eight specimens were collected from IS, mostly (64.29%) from peridomestic areas (mainly chicken coops). No significant (p>0.05) differences were recorded between the two studied cohorts in their average time to hatch, which was close to 19days. The median egg-to-adult development time, the number of blood meals at each nymphal, the instar mortality rates and median time-lapse for beginning of feeding were significantly (p<0.05) shorter for the IS cohort. Median feeding time was higher in PR. Defecation delay was shorter than 10min in both studied cohorts. Given these results, the introduced recently found population of T. lecticularia could be considered an important potential vector of Trypanosoma cruzi to human populations and could replace main triatomine species on its new distribution area.

Developmental study of the Proboscis Extension Response to heat in Rhodnius prolixus along the life cycle

Triatominae are blood-sucking insects that localise their hosts using a range of sensory signals to find food, and among them, the heat emitted by the hosts. Heat is one of the main short-range cues in vertebrate hosts, able to trigger alone the Proboscis Extension Response (PER) that precedes the bite. Previous studies demonstrated that heat responsiveness of fifth-instar nymphs is maximum to moderate temperatures (30-35°C) compatible with those of their vertebrate host's body surface. This study investigated whether this thermal preference for biting is maintained along the life cycle of R. prolixus, from the first larval instar to male and female adults. The results showed that PER rates were at maximum around 30-35°C and decreased for a warmer temperature. The same thermal preference was maintained all along the life cycle, despite the increase in the size of the antennae linked to the growth. Interestingly, a decreased thermal responsiveness was stated in males as compared with larval instars and females. This decrease might reveal a lower motivation for host-seeking and might have an impact on males's vectorial competence.

On triatomines, cockroaches and haemolymphagy under laboratory conditions: new discoveries

For a long time, haematophagy was considered an obligate condition for triatomines (Hemiptera: Reduviidae) to complete their life cycle. Today, the ability to use haemolymphagy is suggested to represent an important survival strategy for some species, especially those in genus Belminus. As Eratyrus mucronatus and Triatoma boliviana are found with cockroaches in the Blaberinae subfamily in Bolivia, their developmental cycle from egg to adult under a “cockroach diet” was studied. The results suggested that having only cockroach haemolymph as a food source compromised development cycle completion in both species. Compared to a “mouse diet”, the cockroach diet increased: (i) the mortality at each nymphal instar; (ii) the number of feedings needed to molt; (iii) the volume of the maximum food intake; and (iv) the time needed to molt. In conclusion, haemolymph could effectively support survival in the field in both species. Nevertheless, under laboratory conditions, the use of haemolymphagy as a survival strategy in the first developmental stages of these species was not supported, as their mortality was very high. Finally, when Triatoma infestans, Rhodnius stali and Panstrongylus rufotuberculatus species were reared on a cockroach diet under similar conditions, all died rather than feeding on cockroaches. These results are discussed in the context of the ecology of each species.

Life Cycle, Feeding, and Defecation Patterns of Panstrongylus chinai (Hemiptera: Reduviidae: Triatominae) Under Laboratory Conditions

Chagas disease is caused by the protozoan Trypanosoma cruzi Panstrongylus chinai (Del Ponte) is highly domiciliated in the Peruvian and Ecuadorian Andes and has been found naturally infected with T. cruzi The objective of this study was to describe the life cycle, feeding, and defecation patterns of P. chinai in the Loja province within southern Ecuador. To characterize its life cycle, a cohort of 70 individuals was followed from egg to adult. At each stage of development, prefeeding time, feeding time, weight of ingested meal, proportional weight increase, and the time to the first defecation were recorded. Panstrongylus chinai completed its development in 371.4 ± 22.3 d, (95% CI 355.4-387.4), which means that it is likely a univoltine species. Prefeeding time, feeding time, and weight of ingested meal increased as individuals developed through nymphal stages. Moreover, time to first defecation was shortest in the early nymphal stages, suggesting higher vector potential in the early developmental stages. Data obtained in this study represent an important advance in our knowledge of the biology of P. chinai, which should be considered as a secondary Chagas disease vector species in the Andean valleys of Loja (Ecuador) and in the north of Peru, and included in entomological surveillance programs.

Transmission Capacity of Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) by Three Subspecies of Meccus phyllosomus (Heteroptera: Reduviidae) and Their Hybrids

Three behaviors of epidemiological importance: the time lapse for the onset of feeding, actual feeding, and defecation time for Meccus phyllosomus pallidipennis (Stål), Meccus phyllosomus longipennis (Usinger), Meccus phyllosomus picturatus (Usinger), and their laboratory hybrids were evaluated in this study. The mean time lapse for the beginning of feeding was between 0.5 and 8.3 min considering all instars in each cohort, with highly significant differences only among fifth-instar nymphs, females, and males of M. p. pallidipennis and M. p. longipennis relative to the hybrid cohorts. Four hybrid (LoPa [M. p. longipennis and M. p. pallidipennis] and LoPi [M. p. longipennis and M. p. picturatus] and their reciprocal experimental crosses) cohorts had similar mean feeding times to one of the parental subspecies, but longer than the other one. The remaining hybrid cohort (PaPi [M. p. pallidipennis and M. p. picturatus]) had longer feeding times than both of its parental subspecies. The specimens of the LoPa and LoPi hybrid cohorts defecated faster than the respective instars of the three parental cohorts. With exception of first- and fifth-instar nymphs, PaPi cohorts defecated faster than the remaining seven cohorts. More than 60% of defecation events occurred during feeding in the six hybrid cohorts. Our results indicate that hybrid cohorts have more potential to acquire infection and transmit Trypanosoma cruzi Chagas than their parental cohorts.

Life cycle and vectorial competence of Triatoma williami (Galvão, Souza e Lima, 1965) under the influence of different blood meal sources

Triatoma williami is naturally infected by Trypanosoma cruzi, the ethiological agent of Chagas disease, the most significant cause of morbidity and mortality in South and Central America.The possibility of domiciliation of T. williami increases the risk of human T. cruzi vetorial transmission. Despite this, there is a lack of data demonstrating the bionomic aspects, the vectorial competence or the natural ecotope and the wild hosts of T. williami. This study describes for the first time the life cycle of T. williami under the influence of two blood meal sources and also evaluates the vectorial potential of the species. The development of two groups of hundred triatomines was followed over the nymphal stages and adulthood. Each group was exposed to a sole blood meal source, mammalian or bird. The average egg-to-adult development time in both groups was similar, except by shorter stages of N3 and N4 in triatomines fed on mammals. The group fed on birds needed more blood feedings to suffer the ecdysis and had higher cumulative mortality in the nymphal stages. Although the observed delay at defecation of adults after feeding, our results suggest that T. williami in the third and fifth nymphal stages may be good vectors.

Importance of Hybrids of Meccus phyllosomus mazzottii, and M. p. pallidipennis, and M. p. phyllosomus to the Transmission of Trypanosoma cruzi in Mexico

The time interval before beginning feeding, feeding time, and defecation delay for 3 Triatominae subspecies, Meccus phyllosomus mazzottii (Ma), M. p. pallidipennis (Pa), and M. p. phyllosomus (Phy) and their laboratory hybrids were evaluated. The mean time interval for beginning feeding was between 0.1 and 10.1 min for all nymphal instars in each cohort, with significant (P < 0.05) differences among hybrids and parental cohorts. Four (both MaPa and MaPhy) hybrid cohorts had similar mean feeding times to that recorded for one of their parental subspecies, but shorter than the other, whereas the remaining hybrid cohorts (both PaPhy) had longer feeding times than did both of their parental subspecies. The specimens of MaPa defecated later than the respective instars on their parental subspecies, whereas most instars of the remaining 4 hybrid cohorts (MaPhy and PaPhy) defecated earlier than the respective instars of M. p. phyllosomus. Between 40% and 50% of the defecation events occurred when feeding in MaPhy and PaPhy hybrid cohorts. Given these results, the hybrid cohorts were more effective vectors of Trypanosoma cruzi than their parental subspecies, which could indicate a potentially higher risk of transmission of T. cruzi to reservoir hosts.