Feeding, defecation, and development times of Meccus longipennis Usinger, 1939 (Hemiptera: Reduviidae: Triatominae) under laboratory conditions

Aspects related to hatching, time-lapse between presenting the blood-meal and beginning of feeding, feeding time, postfeed defecation delay, mortality, and fecundity for each stage of Meccus longipennis life-cycle were evaluated. The bugs were maintained in a dark incubator at 27 1 C and 80 5% rh, were fed weekly and checked daily for ecdysis or death. The hatching rate observed for 300 eggs was 76.7% and the average time of hatching was 19.8 days. Mean time-lapse between presentation of the blood meal and the beginning of feeding was under 5 min in nymphal stages and postfeed defecation delay was under 10 min in most stages, except in fourth and fifth stages. Mean feeding time was longer than 10 min in most stages, except in fourth stage. One hundred thirty-one nymphs (N) (65.5%) completed the cycle and the average time from NI to adult was 192.6 34.8 days. The average span in days for each stage was 18.1 for NI, 21.4 for NII, 29.5 for NIII, 45.5 for NIV and 55.9 for NV. The number of bloodmeals at each nymphal stage varied from 1 to 5. The mortality rate was 3.29 for NI, 6.8 for NII, 2.92 for NIII 3.76 for NIV, and 10.16 for NV nymphs. The average number of eggs laid per female in a 9-month period was 615.6. Based on our results, we conclude that M. longipennis has some biological and behavioral characteristics which influence its capacity of becoming infected and transmitting Trypanosoma cruzi to human populations in those areas of Mexico where it is currently present.     

Influence of the blood meal source on the biology of Meccus picturatus Usinger 1939 (Hemiptera: Reduviidae: Triatominae) under laboratory conditions

Aspects related to hatching, time-lapse between presenting the blood meal and beginning of feeding, feeding time, postfeed defecation delay,life time, mortality and fecundity for each stage of Meccus picturatus, life-cycle were evaluated and compared in two cohorts of M. picturatus fed on hens or rabbits. The hatching rate observed for each of the two studied groups of eggs was 78.1% (n = 2298) on the group fed on hens and 82.1% (n = 2704) on that fed on rabbits, and the average time of hatching was 20 days. Mean time-lapse for beginning feeding was under 3 min in nymphal stages and postfeed defecation delay was under 10 min in all stages, in both cohorts. Mean feeding time was significantly (P < 0.05) shorter in triatomines fed on hens than on rabbits. A similar number of nymphs of each cohort, 69 fed on hens (34.5%) and 68 fed on rabbits (34%), completed the cycle. No significantly (P > 0.05) differences were recorded among the average times from NI to adult in the cohort fed on hens (196.8 15.8 days) and the average time in the cohort fed on rabbits (189.5 22.9). The average span in days for each stage fed on hens was not significantly different to the average span for each stage fed on rabbits. The number of blood meals at each nymphal stage varied from 1 to 6 in both cohorts. The mortality rates were higher on fifth nymphal stage, in both cohorts. No significant (P > 0.05) differences were recorded on mortality rates on most nymphal stages of both cohorts. The average number of eggs laid per female from the cohort fed on hens in a 9-month period was 791.1, whereas the average number of eggs in the cohort fed on rabbits was 928.3.     

Biology of Triatoma pallidipennis stal 1945 (Hemiptera: Reduviidae:Triatominae) under laboratory conditions

Aspects related to hatching, life time, mortality, feeding behaviour and fecundity for each stage of Triatoma pallidipennis life-cycle were evaluated. The hatching rate observed for 200 eggs was 60% and the average time of hatching was 18 days. Eighty nymphs (N) (40%) completed the cycle and the average time from NI to adult was 168. 7+/-11.7days. The average span in days for each stage was 18.0 for NI, 18.5 for NII, 30.0 for NIII, 35.7 for NIV and 50.1 for NV. The number of bloodmeals at each nymphal stage varied from 1 to 5. The mortality rate was 9.17 for NI, 5.5 for NII, 6.8 for NIII 4.17 for NIV and 13.04 for NV nymphs. The average number of eggs laid per female in a 9-month period was 498.6. The survival rates of adults were 357+/-217.9 and 262.53+/-167.7 for males and females respectively.     

Biological and genetic aspects of crosses between species of the genus Meccus (Hemiptera: Reduviidae Triatominae)

The degree of reproductive isolation between Meccus phyllosomus and the remaining five species of the genus Meccus, as well as between Meccus bassolsae and Meccus pallidipennis, Meccus longipennis and Meccus picturatus, was examined. Fertility and the segregation of morphological characteristics were examined in two generations of hybrids from crosses between these species. The percentage of couples with offspring (fertile) was high in the vast majority of sets of crosses, with the exception of that between ♀M. phyllosomus and ♂Meccus mazzottii. In sets of crosses involving M. bassolsae specimens, no first-generation (F1) individuals were morphologically similar to M. bassolsae, but instead shared the morphology of the other parental species. A similar phenomenon was observed in most sets of crosses involving M. phyllosomus. These results indicated that different degrees of reproductive isolation exist among the species of Meccus involved in this study. The biological evidence obtained in this study does not support the proposal that M. bassolsae is a full species. It could indicate that, on the contrary, it should be considered a subspecies of a single polytypic species. The biological evidence does support the proposal that M. phyllosomus is a full species.     

Biology of Triatoma vitticeps (Stal, 1859) under laboratory conditions (Hemiptera: Reduviidae: Triatominae). I. Evolutive cycle

Observations were made on the evolutive cycle of Triatoma vitticeps, held under laboratory conditions and fed weekly in mice. Of the 435 eggs obtained, from 4 virgin couples, 149 were purposed for the biological cycle study and 286 to evaluate their resistance to starvation, which shall be a second part of this work. Only 50 specimens reached the adult stage in a period of means (S) = 270 +/- 45 days. At the incubation time, the first and second instars were of less than a month for each, while the third, fourth and fifth instars requires approximately one, two and three months, respectively. The search for the first meal occurred clearly on the 3rd, 6th and 10th day. During all the stages, more than 50% of the specimens had only one blood-meal, except the fifth one, when two blood-meals were required. In relation to the time-lapse between the presenting of the blood-meal and the beginning of feeding, as well as the length of the blood-meal, it was observed that these increased gradually according to the stage. From the 423 blood-meals performed, 390 were not followed by defecation in the settled period of 10 min. Under this point of view, T. vitticeps seems to be a poor transmissor of T. cruzi. The experiment was carried out for 13 months and by this time the averages of minimum and maximum temperatures and the humidity were 25 +/- 2 degrees C - 28 +/- 2 degrees C and 80 +/- 2%, respectively. The material belongs to the triatomine colony held at the Oswaldo Cruz Institute, Department of Entomology.     

Biology of Triatoma vitticeps (Stal, 1859) under laboratory conditions (Hemiptera: Reduviidae: Triatominae). II. Resistance to fasting

Following the study on the biology of Triatoma vitticeps (Gon?alves et al., 1988) observations have been made on its resistance to starvation. Of the 286 eggs obtained only 201 hatched and reached the intended stage for observation. The others did not eclode, neither reached the ecdisis nor died, without explanation. The nymphs were kept, separately, in Borrel flasks and properly listed. The blood-meal was performed in mice, although the insects were kept without feeding as soon as moulted. The starvation was evaluated in two ways: the time-lapse in days between the last meal/death and between moult/death. The starvation was directly related with the developmental stage. In relation to the parameters last meal/death and moult/death, both sexes were less resistant than 3rd and 2nd stage, respectively. The experiment have been carried out for 15 months and by this time the average minimum and maximum temperatures and the humidity were 25 +/- 2 degrees C - 28 +/- 2 degrees C and 81 +/- 3% UR, respectively. The material spent belongs to the triatomine colony of the Oswaldo Cruz Institute Department of Entomology.     

Resistance to starvation of Rhodnius neivai Lent, 1953 (Hemiptera: Reduviidae: Triatominae) under experimental conditions

The period of resistance to starvation and the loss of weight until death of Rhodnius neivai in all stages of development were studied. Work was based on experiments conducted under controlled laboratory conditions. One hundred specimens of each nymphal instar were observed: 50 were fed on chicken and 50 on rabbit. Adult females and males were kept together and fed on each host. All bugs were weighed weekly until death. Laid eggs were collected weekly and observed during five weeks to obtain hatchability. Resistance to starvation was similar with both hosts and increased with the evolutionary stage, excepting the 5th nymphal instar and adults. With both hosts, loss of weight was abrupt in the first week and steady in the following weeks. In adults, on the first weeks after eating, there was little or no mortality, after which mortality increased rapidly with the starving time. Reproductive output was higher in the bugs fed on rabbit. R. neivai is among the least resistant triatomine species.     

Morphologic, morphometrical, and histological aspects of the eggs of four species of the genera Meccus (Hemiptera, Reduviidae, Triatominae)

The objective of this work was to analyze the morphological, morphometrical, and histological characteristics of eggs of four triatomine bugs species still not studied, in order to understand phylogenetic aspects and to facilitate parameters used in taxonomy, with the purpose of a specific and generic characterization of these vectors in public health. The eggs of each species had come from the collections of the Laboratory of Triatomine bugs and Culicid mosquitoes of the Faculdade de Saúde Pública - USP (Faculty of Public Health/USP). The morphologic studies were carried out through optic microscopy (OM) and scanning electronic microscopy (SEM). The eggs were measured with the help of the digital paquimeter Starrett 727. In relation to histological measures, Microtome Leica RM 2145 was used. Similarities were evidenced in the exocorial architecture of the eggs when they were studied by OM and SEM. This similarity among the eggs suggests a recent speciation, probably derived from common ancestry, representing a monophyletic group. Some structures were also detected by the histological cuts. The study has contributed to the magnification and recognition in generic and specific terms of the Triatominae subfamily. These new data will be able to subsidize a better understanding to determine roles for each vector species and to facilitate parameters to be used in taxonomy.     

Biology of three species of the Meccus phyllosomus complex (Hemiptera: Reduviidae: Triatominae) fed on blood of hens and rabbits

Aspects related to hatching, life time, number of blood meals to molt, mortality, feeding time and postfeed defecation delay for each instar of Meccus phyllosomus, M. mazzottii, and M. bassolsae, life-cycle were evaluated and compared in two cohorts of each of those three species, fed on hens or rabbits. No significant (p > 0.05) differences were recorded among cohorts fed on hens respect to cohorts fed on rabbits in M. phyllosomus and M. mazzottii and the average time of hatching was 21.5 days for cohorts fed on hens and 22.5 for cohorts fed on rabbits. Average egg-to-adult development times were no significant (p > 0.05) different between both cohorts of M. phyllosomus and M. mazzotti, independent of the blood meal source. The average span in days for each instar fed on hens was not significantly different to the average span for each instar fed on rabbits, when comparisons were made by species. The number of blood meals at each nymphal instar varied from 1 to 6 in both cohorts of each species. The mortality rates were higher on older nymphs, in both cohorts of M. phyllosomus and M. bassolsae, whereas they were higher on first instar nymphs on M. mazzottii. Mean feeding time was no significant (p > 0.05) different in triatomines fed on hens or fed on rabbits, when each species were compared separately. A similar number of nymphs of each cohort, completed the cycle. Defecation delay was no significant (p > 0.05) different when cohorts fed on hens and fed on rabbits were compared by species. Most of the studied parameters showed no significant (p > 0.05) differences among those cohorts fed on hens and for fed on rabbits, which could mean a high degree of association of those species with birds as much as mammals, under wild conditions, increasing their capacity to colonize human dwellings.     

Defecation index and reproductive success of Triatoma maculata (Hemiptera: Reduviidae) under laboratory conditions

The reproductive and defecating behavior of Triatoma maculata (Erichson 1848) was studied on animals from an university culture in Venezuela. This species does not reach the importance of Rhodnius prolixus Stal 1859 as Chagas disease vector in Venezuela. This study addressed the role of defecating frequency, an index of how dangerous the animals are for the human population, and its relationship with why T. maculata is a less important vector than R. prolixus. Human blood was fed to the insects through an artificial feeding device. The 2nd and 3rd instar nymphs defecated more frequently (Id= 0.6, n=40), and our Vth instar nymphs did not complete sexual differentiation. Fertility was 55% (n=865) and fecundity 8 eggs/female/week (n=26). Egg incubation lasted 22 days (n=477). Female longevity was 51 days (n=26). Intermould time grew progressively from 35 days for 1st to 40 days for 4th instar nymphs (n=40). Mould percentage varied from 0% for Vth to 63% for 3rd instar nymphs. Mortality varied from 8% for 3rd to 100% for Vth instar nymphs. These results support evidences explaining the lesser vectorial capacity and low density of T. maculata in human domiciles, including reduced reproduction and defecation when the animal feeds on human blood.     

Ecological patterns of blood-feeding by kissing-bugs (Hemiptera: Reduviidae: Triatominae)

Host use by vectors is important in understanding the transmission of zoonotic diseases, which can affect humans, wildlife and domestic animals. Here, a synthesis of host exploitation patterns by kissing-bugs, vectors of Chagas disease, is presented. For this synthesis, an extensive literature review restricted to feeding sources analysed by precipitin tests was conducted. Modern tools from community ecology and multivariate statistics were used to determine patterns of segregation in host use. Rather than innate preferences for host species, host use by kissing-bugs is influenced by the habitats they colonise. One of the major limitations of studies on kissing-bug foraging has been the exclusive focus on the dominant vector species. We propose that expanding foraging studies to consider the community of vectors will substantially increase the understanding of Chagas disease transmission ecology. Our results indicate that host accessibility is a major factor that shapes the blood-foraging patterns of kissing-bugs. Therefore, from an applied perspective, measures that are directed at disrupting the contact between humans and kissing-bugs, such as housing improvement, are among the most desirable strategies for Chagas disease control.     

Biology of three species of North American Triatominae (Hemiptera: Reduviidae: Triatominae) fed on rabbits

Aspects related to hatching, lifetime, number of blood meals for molting, mortality, feeding time, and postfeeding defecation delay were evaluated and compared in each instar of three North American Triatominae: Triatoma gerstaeckeri, Triatoma lecticularia and Triatoma protracta, all of them fed on rabbits. No significant differences (p > 0.05) were found among the three species regarding mean hatching rate, which was close to 20 days. Egg-to-adult development times were significantly shorter (p < 0.05) for T. lecticularia. Number of blood meals for molting to next instar ranged from one to five for T. protracta, and from one to six for T. gerstaeckeri and T. lecticularia. Mortality rates were higher in younger nymphs of T. lecticularia and T. protracta, while rates in T. gerstaeckeri were higher in fifth-instar nymphs. Mean feeding time was longest in T. gerstaeckeri, followed by T. lecticularia. More than twice the number of T. gerstaeckeri nymphs completed the development process, if compared to the nymphs from the other two species. Defecation delay was less than 10 min for T. lecticularia, T. protracta and the youngest nymphs of T. gerstaeckeri. Results point out that these three species may be important potential vectors of Trypanosoma cruzi for human populations, in areas of Mexico where these species are currently present.     

Diapause induction under greenhouse conditions in two populations of Dicyphus hesperus (Hemiptera: Miridae)

The effects of daylength on induction of reproductive diapause were investigated in two populations of Dicyphus hesperus to determine which was more suitable as a biological control in greenhouses without supplemental light. A population from British Columbia Canada (49°36' N Lat.) had a critical daylength of about 15.5 h, whereas that of a population from California, USA (35°43' N Lat.) was between 14.0 and 13.5 h. Under natural daylengths in greenhouses at 49°N Lat., females of both populations exhibited reproductive diapause at a daylength that was consistent with their respective critical daylengths. In spring, a lower proportion of both populations diapaused when exposed to diapause-inducing conditions than in autumn. Reproductive diapause of the females of the BC population was 100% in autumn, but half of those females laid eggs when held in the greenhouse for 6 weeks. A maximum of 63% of females of the California population diapaused in autumn, and most began to lay eggs after 2 weeks. The differences in response to daylength presumably reflect differences between the two localities in the reliability of the critical daylength as a predictor of conditions unsuitable for growth and reproduction. Under greenhouse conditions the California population is essentially non-diapausing, and would be the more suitable of the two populations for use as a biological control agent.     

Effects of Metarhizium anisopliae on Meccus pallidipennis (Hemiptera: Reduviidae) over different types of wall surfaces

The entomopathogenic fungus Metarhizium anisopliae is virulent for the insect triatomine Meccus pallidipennis. To evaluate the functionality of a fungal formulation (vegetable oil and emulsifiers) of this fungus, virulence was assayed by insect mortality on the pronotum of third instar nymphs (N3) M. pallidipennis in laboratory conditions and ST₅₀ was calculated. Mortality was evaluated directly: 100%, 97.33% and 98.66% mortalities were caused by formulation, emulsified formulation and fungal conidia, respectively, at day 8 of insect infection. Another bioassay was carried out in simulated external conditions (peridomicility) using red and gray brick walls, a stone fence and mountain soil (experimental units). These simulated conditions were infected with 10?ml of a 1?×?10⁹?conidia/ml emulsified formulation by means of a manual sprinkler prior to the placement of the nymphs. Ten N3 M. pallidipennis were deposited in each experimental unit and insect mortality was monitored every 12?h for 22 days. Each treatment was replicated four times. With the red brick wall, a mortality of 90% at day 22 and a ST₅₀ of 15 days were obtained on N3 M. pallidipennis; with the gray brick wall, 100% mortality and a ST₅₀ of 13 days; and with the stone fence, 88.33% mortality and a ST₅₀ of 21 days. The results obtained in this research work indicate that the formulation with conidia of the M. anisopliae strain EH-473/4 may be auxiliary in the development of strategies for the control of Chagas disease insect transmitters such as M. pallidipennis.     

Presence of Panstrongylus rufotuberculatus (Champion, 1899) (Hemiptera: Reduviidae: Triatominae) in Argentina.

Panstrongylus rufotuberculatus is reported for the first time in Argentina. Four adults were attracted by the light of human dwellings in Calilegua National Park, Jujuy, at 1150 masl within the subtropical humid forest. The individuals were similar to those described in the literature. The epidemiological significance of this species is very low in the area, although deforestation might increase its role in the transmission of Trypanosoma cruzi.     

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.     

Life history of Paracoccus marginatus (Hemiptera: Pseudococcidae) on four host plant species under laboratory conditions

Life history of the mealybug, Paracoccus marginatus Williams and Granara de Willink, on three ornamental plants [Hibiscus rosa-sinensis L., Acalypha wilkesiana (Muell.-Arg.), and Plumeria rubra L.] and one weed species (Parthenium hysterophorus L.) was studied under laboratory conditions. Mealybugs were able to develop, survive, and reproduce on all four hosts; however, there were differences in the life history parameters. Adult females that developed on acalypha and parthenium emerged approximately 1 d earlier than those that developed on hibiscus and plumeria. Adult males had a longer developmental time on plumeria than on the other hosts. Survival of first- and second-instar nymphs and cumulative adult survival were lowest on plumeria. Longevity was not affected by hosts for males and females and averaged 2.3 +/- 0.1 and 21.2 +/- 0.1 d, respectively. On plumeria, 58.9 +/- 1.7% of the adults were females, which was a higher female percentage than on the other hosts. No egg production occurred in virgin females. Prereproductive and reproductive periods of the females were not affected by hosts and averaged 6.3 +/- 0.1 and 11.2 +/- 0.1 d, respectively. Mean fecundity of 186.3 +/- 1.8 eggs on plumeria was lower than on the other three plant species. Life history parameters of P. marginatus on hibiscus, acalypha, plumeria, and parthenium show its ability to develop, survive, and reproduce on a wide variety of plant species.     

Vital statistics of Rhodnius neivai Lent, 1953 (Hemiptera: Reduviidae) under experimental conditions

A statistical evaluation of the population dynamics of R. neivai is based on six cohorts experiments conducted under controlled laboratory conditions. Two blood sources were offered to animals: rabbit and hen. Egg hatching, nymphal development time and mortality, adult longevity and age-specific mortality, female age-specific fecundity and fertility were determined. In addition, some population parameters were evaluated, such as: life expectancy, intrinsic rate of natural increase, net reproduction rate, finite rate of increase, reproductive value and stable age distribution. Life cycle was longer in the animals fed on rabbit, nymphal survival was slightly higher in the individuals fed on hen. Age of first reproduction was lower in the insects fed on hen, but reproductive output and total number of reproductive weeks were greater in the cohorts fed on rabbit. Intrinsic and finite rate of increase were greater in the animals fed on hen. Generation time was slightly greater in the cohorts fed on rabbit. Net reproduction rate was similar on both blood sources, although it was slightly bigger in the individuals fed on rabbit. Reproductive value in the insects fed on rabbit was twice as much as the registered in the animals fed on hen.