Machine-learning model led design to experimentally test species thermal limits: The case of kissing bugs (Triatominae)

Species Distribution Modelling (SDM) determines habitat suitability of a species across geographic areas using macro-climatic variables; however, micro-habitats can buffer or exacerbate the influence of macro-climatic variables, requiring links between physiology and species persistence. Experimental approaches linking species physiology to micro-climate are complex, time consuming and expensive. E.g., what combination of exposure time and temperature is important for a species thermal tolerance is difficult to judge a priori. We tackled this problem using an active learning approach that utilized machine learning methods to guide thermal tolerance experimental design for three kissing-bug species: Triatoma infestans, Rhodnius prolixus, and Panstrongylus megistus (Hemiptera: Reduviidae: Triatominae), vectors of the parasite causing Chagas disease. As with other pathogen vectors, triatomines are well known to utilize micro-habitats and the associated shift in microclimate to enhance survival. Using a limited literature-collected dataset, our approach showed that temperature followed by exposure time were the strongest predictors of mortality; species played a minor role, and life stage was the least important. Further, we identified complex but biologically plausible nonlinear interactions between temperature and exposure time in shaping mortality, together setting the potential thermal limits of triatomines. The results from this data led to the design of new experiments with laboratory results that produced novel insights of the effects of temperature and exposure for the triatomines. These results, in turn, can be used to better model micro-climatic envelope for the species. Here we demonstrate the power of an active learning approach to explore experimental space to design laboratory studies testing species thermal limits. Our analytical pipeline can be easily adapted to other systems and we provide code to allow practitioners to perform similar analyses. Not only does our approach have the potential to save time and money: it can also increase our understanding of the links between species physiology and climate, a topic of increasing ecological importance.

Systematic review on the biology, ecology, genetic diversity and parasite transmission potential of Panstrongylus geniculatus (Latreille 1811) in Latin America

Panstrongylus geniculatus (Latreille, 1811) is the triatomine with the largest geographic distribution in Latin America. It has been reported in 18 countries from southern Mexico to northern Argentina, including the Caribbean islands. Although most reports indicate that P. geniculatus has wild habitats, this species has intrusive habits regarding human dwellings mainly located in intermediate deforested areas. It is attracted by artificial light from urban and rural buildings, raising the risk of transmission of Trypanosoma cruzi. Despite the wide body of published information on P. geniculatus, many knowledge gaps exist about its biology and epidemiological potential. For this reason, we analysed the literature for P. geniculatus in Scopus, PubMed, Scielo, Google Scholar and the BibTriv3.0 databases to update existing knowledge and provide better information on its geographic distribution, life cycle, genetic diversity, evidence of intrusion and domiciliation, vector-related circulating discrete taxonomic units, possible role in oral T. cruzi transmission, and the effect of climate change on its biology and epidemiology.

Structure and function of the stylets of hematophagous Triatominae (Hemiptera: Reduviidae), with special reference to Dipetalogaster maxima

Kissing bugs (Hemiptera: Reduviidae: Triatominae) are able to bend their rod-like maxillae while searching for blood vessels in the tissue of their vertebrate hosts. Little is known about the working mechanisms of these bending movements and the distal opening of the food channel. We compared the morphological structure of the stylets (mandibles and maxillae) of four triatomine species and analyzed the feeding process of Dipetalogaster maxima (Uhler, 1894). The maxillae of triatomine bugs are interlocked by a tongue-and-groove system, allowing longitudinal sliding. While penetrating the host tissue, the animals perform rapid alternate back and forth movements of the maxillae. The resistance of the surrounding tissue pushes the asymmetric apex of the maxillae away from its straight path, i.e., if one individual maxilla is protracted alone, its tip curves inwards, and the other maxilla follows. Once a blood vessel is tapped, the spine-like tip of the left maxilla splays outwards. Apically, each of the maxillae features an abutment, the left one exhibiting a notch that presumably facilitates splaying. The mechanical interaction of the two maxillary abutments enables the distal opening of the food channel but might also support the movements of the maxillary bundle attributable to different bending moment distributions.

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.

Vital Statistics of Triatominae (Hemiptera: Reduviidae) Under Laboratory Conditions: IV. Panstrongylus geniculatus

A cohort of 100 eggs of Panstrongylus geniculatus (Latreille) was reared in the laboratory under constant conditions (temperature 26 ± 1°C, 60 ± 10% RH), with mortality and fecundity data recorded weekly. We calculated stage-specific development times, age-specific mortality and fecundity (18.4 eggs/♀/wk), and stage-specific and total preadult mortality (31.6%), and the weekly intrinsic rate of natural increase (r(o) = 0.096), the finite population growth rate (λ = 1.109), the net reproductive rate (R(0) = 60.45), and the generation time (T = 46.34 wk). Elasticity analysis showed that the dominant life-history trait determining λ was survival (particularly the adult female's survival). Adult females dominated the stage-specific reproductive value, and the egg stage dominated the stable stage distribution (SSD). The damping ratio (ρ = 1.096) suggests a relatively rapid period of recovery to a disturbed SSD. Results were compared with one previous study and conform relatively well, considering that environmental conditions were not the same. We estimated the colonizing ability of P. geniculatus, using as a criterion the ro/b index, and obtained the value of 0.74, an indicator of a good colonizer, and similar to well-known invasive species such as Rhodnius prolixus and Triatoma infestans. The life history traits and demographic parameters here presented for P. geniculatus are discussed in terms of their usefulness for evolutionary studies and vector control activities.

Amines from vertebrates guide triatomine bugs to resources

Most triatomine bugs (Heteroptera: Reduviidae) are nest-living insects that require vertebrate blood or invertebrate haemolymph to complete their life cycle. Vertebrates accumulate excretory products in or near their nesting sites and we hypothesize that triatomines use emanations from such host wastes when searching for resources. Here we recount how triatomine bugs increase upwind locomotion on a servosphere in response to volatile amine constituents of vertebrate excretions. Fresh chicken faeces is strongly attractive to Rhodnius prolixus nymphs. Ammonia induces attraction and an increase in both speed and total path length by R. prolixus on the servosphere. Whereas ethylamine and dimethylamine attract R. prolixus, Triatoma infestans and Panstrongylus geniculatus, other amine constituents of vertebrate excretions such as isobutylamine and hexylamine induce R. prolixus nymphs to walk faster and for a longer period. These amines are derived from generally occurring metabolites of vertebrates and from gut flora metabolism. We conclude that amines and other products associated with nesting hosts serve as signals for foraging triatomines.

A multi-species bait for Chagas disease vectors

Background

Triatomine bugs are the insect vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. These insects are known to aggregate inside shelters during daylight hours and it has been demonstrated that within shelters, the aggregation is induced by volatiles emitted from bug feces. These signals promote inter-species aggregation among most species studied, but the chemical composition is unknown.

Methodology/Principal Findings

In the present work, feces from larvae of the three species were obtained and volatile compounds were identified by solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). We identified five compounds, all present in feces of all of the three species: Triatoma infestans, Panstrongylus megistus and Triatoma brasiliensis. These substances were tested for attractivity and ability to recruit insects into shelters. Behaviorally active doses of the five substances were obtained for all three triatomine species. The bugs were significantly attracted to shelters baited with blends of 160 ng or 1.6 µg of each substance.

Conclusions/Significance

Common compounds were found in the feces of vectors of Chagas disease that actively recruited insects into shelters, which suggests that this blend of compounds could be used for the development of baits for early detection of reinfestation with triatomine bugs.

Chagas disease is a parasitic infection affecting approximately 12 million people, and is considered to be one of the most severe burdens for public health in Latin America. Control of the disease is based on attempted elimination of domestic populations of triatomine bugs, the insects transmitting the disease to humans, by means of insecticide spraying. Currently, vigilance programs monitoring triatomine reinfestation processes in houses are performed by manual search for bugs. Effective and sustainable new methods allowing continuous monitoring of domestic triatomine populations are required. Based on the fact that the insects hide in dark refuges that are marked by volatile signals emitted in their feces, we screened the feces of three species for volatile compounds common to these prominent vectors. The potential for these odors to promote triatomine aggregation was evaluated and we present evidence that a synthetic blend of these substances is capable of recruiting bugs into shelters, mimicking the natural pheromone. This blend may be used to develop a bait to monitor triatomine reinfestation processes in a similar manner as is used commonly for the monitoring of agricultural pests.

Competitive displacement in Triatominae: the Triatoma infestans success

Brazil has just been certificated by Pan American Health Organization as 'free of Chagas disease transmission due to Triatoma infestans'. During the early 1980s, this species of blood-sucking bug alone was considered responsible for approximately 80% of Chagas disease transmission. But it was not always so. The species originally abundant in houses of central and eastern Brazil was Panstrongylus megistus, which seems to have been progressively displaced from houses by T. infestans during the past century. Indeed, T. infestans seems able to displace other Triatominae in artificial environments. Recent studies suggest that it might simply be because T. infestans feeds more efficiently than its Triatominae competitors.

Estudo das fontes alimentares de Panstrongylus lutzi (Neiva & Pinto, 1923) (Hemiptera: Reduviidae: Triatominae) no Estado do Ceará

Os autores utilizaram a técnica de precipitina para identificar as fontes alimentares de Panstrongylus lutzi (Neiva & Pinto, 1923) em 20 municípios do Estado do Ceará, Brasil. Os resultados detectaram a presença de sangue de oito diferentes fontes sanguíneas e alimentações mistas, demonstrando que Panstrongylus lutzi é uma espécie eclética. Altas taxas de infecção por tripanosomatídeos foram detectadas.

[Rupestrian triatomines infected by Trypanosomatidae, collected in Quaraí, Rio Grande do Sul, 2003]

Rupestrian triatomines were captured in six Quaraí city localities, RS, to verify the level of Trypanosomatidae infection, as well as the animal reservoir. The capture occurred in a wild environment and 453 samples were collected, which were identified and separated by nymphal instar. 421 (92.9%) samples of Triatoma rubrovaria, 26 (5.7%) of Triatoma circummaculata and 6 (1.3%) of Panstrongylus tupynambai were collected. Only 13 samples (4.2%) of Triatoma rubrovaria presented Trypanosomatidae infection. After mice and LIT culture inoculation, five strains of Trypanosoma cruzi were isolated. Of these triatomines, 4 (30.8%) displayed no reagent precipitin for the antiserum tested, 4 (30.8%) were positive for rodent antiserum, 4 (30.8%) were positive for goat antiserum and 1 (7.7%) were positive for human and pig antiserum.

Stridulatory sound emission of Panstrongylus rufotuberculatus Champion, 1899, (Hemiptera: Reduviidae: Triatominae)

This study contains the first report of stridulatory sound observed in Panstrongylus rufotuberculatus Champion, 1899, and also a new record of this species in Venezuela. The conditions in which stridulation occurred are described, as well as the general environmental characteristics of the localities where it was found. This triatomine only performs the sound in conditions of extreme provocation.

A preliminary study of haemolymph from four Venezuelan populations of Panstrongylus geniculatus Latreille, 1811 (Hemiptera: Reduviidae) and its epidemiological significance

SDS-PAGE profiles of both sexes of the haemolymphs of Panstrongylus geniculatus from different Venezuelan regions (savannas, piedmont, tropical forest and urban areas) were compared. It was determined that the haemolymphs showed a different electrophoretic profile, with proteins that ranged from 14 to 164 kDa. The most representative protein band in the profile of females was observed in two sectors: between 164 and 46 kDa and between 33 and 30 kDa. The main illustrative protein band in males was observed in one region: from 46 to 35 kDa. The Haemolymph composition of P. geniculatus from populations evaluated in this work expressed high homogeneity of this species with a clear difference between males and females. This similarity may be useful for control of these insects, taking into account that the genetic stability may be very important, since the use of an insecticide in a population with these characteristics is always more successful. According to the bibliographic review, this is the first study of haemolymph from Panstrongylus geniculatus.

Variability of the salivary proteins of 20 Brazilian populations of Panstrongylus megistus (Hemiptera: Reduviidae: Triatominae)

The objective of the present study was to study variability in the salivary proteins of 20 Panstrongylus megistus populations from different ecotopes and verify whether this variability influenced the intensity of the response to specific anti-saliva antibodies. Electrophoretic analysis of P. megistus saliva showed a complex protein composition and great interpopulation variability. A higher concentration of bands was observed in the 17-29 kDa region. The phenogram constructed from the electrophoretic profiles of the P. megistus study populations revealed the existence of two main groups. However, there was no evident relationship between these groups and geographical regions, ecotopes or hosts. Saliva inoculated by P. megistus during feeding elicited production of low level of anti-saliva antibodies in rabbit. The homologous and heterologous salivary proteins were recognised by serum of rabbit sensitised with saliva from only one population. Qualitative and quantitative differences were observed for recognised bands in the saliva of all eight populations studied by Western blot analysis. The most recognised bands were those of greatest molecular weight (68.0-97.4 kDa).

The sexual behaviour of Panstrongylus megistus (Hemiptera: Reduviidae): an experimental study

The factors affecting the sexual behaviour of Panstrongylus megistus were studied under laboratory conditions. A general description of mating behaviour is presented for this species. The effect of the time elapsed after the first imaginal feeding on the mating frequency, the motivation of males to mate and the rejection behaviour by females, were analyzed. We also determined the number of copulas accepted by females of this species. Finally, the possible existence of a sexual chemical signal promoting male aggregation around mating couples was evaluated. Results showed that mating frequency increased with the time elapsed since the first adult meal. Despite the number of male copulatory attempts did not change as a function of time, the rejection behaviour of females became gradually less frequent. Females rejected mating by means of body flattening on the substrate, abdominal movements, evasion or stridulation. After a single copula, females did not usually accept to mate again. Neither male nor female aggregation around mating couples was observed, suggesting the absence of a sexual assembling pheromone in P. megistus.

Flight metabolism in Panstrongylus megistus (Hemiptera: Reduviidae): the role of carbohydrates and lipids

The metabolism of lipids and carbohydrates related to flight activity in Panstrongylus megistus was investigated. Insects were subjected to different times of flight under laboratory conditions and changes in total lipids, lipophorin density and carbohydrates were followed in the hemolymph. Lipids and glycogen were also assayed in fat body and flight muscle. In resting insects, hemolymph lipids averaged 3.4 mg/ml and significantly increased after 45 min of flight (8.8 mg/ml, P < 0.001). High-density lipophorin was the sole lipoprotein observed in resting animals. A second fraction with lower density corresponding to low-density lipophorin appeared in insects subjected to flight. Particles from both fractions showed significant differences in diacylglycerol content and size. In resting insects, carbohydrate levels averaged 0.52 mg/ml. They sharply declined more than twofold after 15 min of flight, being undetectable in hemolymph of insects flown for 45 min. Lipid and glycogen from fat body and flight muscle decreased significantly after 45 min of flight. Taken together, the results indicate that P. megistus uses carbohydrates during the initiation of the flight after which, switching fuel for flight from carbohydrates to lipids.

Experimentally induced heat- and cold-shock tolerance in adult Panstrongylus megistus (Burmeister) (Hemiptera, Reduviidae)

The survival rate of domestic male and female adult Panstrongylus megistus was studied after sequential heat and cold shocks in order to investigate shock tolerance compared to that previously reported for nymphs. Sequential shocks were such that a milder shock (0°C, 5°C, 35°C, or 40°C for 1 h) preceded a severe one (0°C or 40°C for 12 h), separated by intervals of 8, 18, 24, and 72 h at 28°C (control temperature). The preliminary thermal shock induced tolerance to the more severe one, although tolerance intensity depended on the initial shock temperature and the interval between treatments. Despite the observed tolerance, the survival rate for insects subjected to both shocks decreased when compared to that of individuals subjected to a single mild shock. When tolerance differed with sex, females showed greater values than males. In contrast to the response detected in nymphs, for which higher heat tolerance values were sustained for intervals of up to 24 h (preliminary shock, 35ºC) or even longer (preliminary shock, 40ºC) between sequential shocks, significant values were verified in adults only for shock intervals of up to 8 h (preliminary shock, 40ºC). While findings for nymphs exhibited considerable cold-shock tolerance under conditions in which preliminary shocks were given at 5ºC or 0ºC and the periods between shocks were up to 72 h long, the adults were shown to be capable of acquiring a substancial tolerance response to a more severe cold shock only when the preliminary shock was given at 0ºC and shock interval surpassed 18 h. It is assumed that the mechanisms involved in the cellular protection of P. megistus under sequential temperature shocks (heat shock protein action?) may loose effectiveness with insect development.

Effect of sequential heat and cold shocks on nuclear phenotypes of the blood-sucking insect, Panstrongylus megistus (Burmeister) (Hemiptera, Reduviidae)

Thermal shocks induce changes in the nuclear phenotypes that correspond to survival (heterochromatin decondensation, nuclear fusion) or death (apoptosis, necrosis) responses in the Malpighian tubules of Panstrongylus megistus. Since thermal tolerance increased survival and molting rate in this species following sequential shocks, we investigated whether changes in nuclear phenotypes accompanied the insect survival response to sequential thermal shocks. Fifth instar nymphs were subjected to a single heat (35 or 40 degrees C, 1 h) or cold (5 or 0 degrees C, 1 h) shock and then subjected to a second shock for 12 h at 40 or 0 degrees C, respectively, after 8, 18, 24 and 72 h at 28 degrees C (control temperature). As with specimen survival, sequential heat and cold shocks induced changes in frequency of the mentioned nuclear phenotypes although their patterns differed. The heat shock tolerance involved decrease in apoptosis simultaneous to increase in cell survival responses. Sequential cold shocks did not involve cell/nuclear fusion and even elicited increase in necrosis with advancing time after shocks. The temperatures of 40 and 0 degrees C were more effective than the temperatures of 35 and 5 degrees C in eliciting the heat and cold shock tolerances, respectively, as shown by cytological analysis of the nuclear phenotypes. It is concluded that different sequential thermal shocks can trigger different mechanisms of cellular protection against stress in P. megistus, favoring the insect to adapt to various ecotopes.

Dynamics of thermopreference in the Chagas disease vector Panstrongylus megistus (Hemiptera: Reduviidae)

The thermopreference of resting P. megistus (Burmeister, 1834) adults was studied in a temperature gradient. We also determined the thermopreference for oviposition and ecdysis. Thermopreference of resting individuals depended on the feeding state of the insects. Results demonstrated an initial resting preference of approximately 290 degrees C, which gradually changed to 26-27 degrees C with increasing starvation. A daily variation in thermopreference was also observed with this species. The insects showed a daily maximum preference at the beginning of the dark phase, and a minimum preference during the first half of the light phase. Ecdysis took place all along the gradient, but exhibited a maximum frequency at 30 degrees C. Most eggs were found between 25 and 29 degrees C. Results are discussed in relation to the ecology of P. megistus as compared with other related species, and the existence of mechanisms of behavioral thermoregulation in the group.

Aggregation behaviour in Panstrongylus megistus and Triatoma infestans: inter and intraspecific responses

We tested the aggregation response to inter and intraspecific chemical signals in Panstrongylus megistus and Triatoma infestans. As previously described for T. infestans, larvae of P. megistus significantly aggregated on papers impregnated with their own excrement and on papers marked with cuticular substances deposited on surfaces on which these insects had walked. T. infestans bugs also aggregated on papers impregnated by faeces or by cuticular substances of P. megistus, and P. megistus aggregated on papers contaminated by faeces or by cuticular substances of T. infestans. The response of P. megistus to its cuticular substances was significantly stronger than that to its faeces. The non-specificity of the two signals is discussed in the context of the ecological relationship between both species.

Experimental evidence for a demographic cline in Panstrongylus megistus populations

The population biology of three populations of Panstrongylus megistus was compared to determine possible influence on the behaviour and epidemiological importance of this species. The results demonstrated differences in terms of egg eclosion time, nymphal mortality and development rates, and feeding and defaecation rates. These differences appeared to follow a geographical cline, primarily reflecting different degrees of adaptation to domestic habitats.

Experimentally induced heat-shock tolerance in Panstrongylus megistus (Hemiptera: Reduviidae)

The survival and molting incidence of fifth-instar nymphs of Panstrongylus megistus (Burmeister, 1835), a vector of Chagas' disease, were investigated following sequential heat shocks in which a mild shock (35 or 40 degrees C, 1 h) preceded a more drastic one (40 degrees C, 12 h). The shocks were separated by 8-, 18-, 24-, or 72-h periods at 28 degrees C. The heat-shock tolerance response was more effective when the first shock was given at 40 degrees C. When the period between shocks was 18 h, the tolerance to sequential shocks (in terms of specimen survival) weakened, which suggested a transient control of the process that enables the organism to circumvent the unfavorable effects of severe shock. In terms of molting incidence, the heat-shock tolerance was only demonstrated when the period between the first shock at 40 degrees C for 1 h and the second shock at 40 degrees C for 12 h was > or = 24 h. These results are the first to demonstrate the induction of heat-shock tolerance in a blood-sucking hemipteran.

[Effects of food deprivation levels on the oogenesis of Panstrongylus megistus]

The effects of various levels of food deprivation on the oogenesis of P. megistus was studied. Immediately after the imaginal ecdysis, six groups (GI to GVI) of 15 couples each were formed. Each group was fed as follows: GI -- on days 5 and 25; G-II -- on days 5 and 35; GIII -- on days 5 and 45; GIV -- on day 20; GV -- on day 30; GVI -- on day 40 after the imaginal ecdysis. After the established fasting period, all groups were fed fortnightly. Fifteen couples were in the control group (CG), which was fed on the day 5 after the imaginal ecdysis and subsequently fortnightly. GI produced more eggs, matings and fertile eggs. GII had longer life spans, higher fecundity and hatchings. GIII had a shorter life span, low fecundity, fertility and hatchings. GVI presented the least favorable results for all parameters, except for the pre-oviposition period. The CG had the best results in all parameters when compared with all experimental groups.

Effect of sequential cold shocks on survival and molting incidence in Panstrongylus megistus (Burmeister) (Hemiptera, Reduviidae)

The survival and molting incidence were studied in the insect, Panstrongylus megistus, following sequential cold shocks in which a milder shock at 0 or 5 degrees C for 1 h preceded a more severe shock (0 degrees C, 12 h). The shocks were separated by intervals of 8, 18, 24, and 72 h at 28 degrees C. The survival rate after sequential shocks was identical to that of unshocked controls. Cold-shock tolerance differed from heat-shock tolerance since the latter varied with the time between shocks and was much more transient. Sequential cold shocks produced a higher molting incidence when the first shock was given at 0 compared to 5 degrees C. This response was more rapid than that to sequential heat shocks. Cold-shock tolerance in P. megistus may involve heat-shock proteins, although other protective mechanisms may also occur concurrently. This is the first report of cold-shock tolerance in a blood-sucking hemipteran.

Changes in nuclear phenotypes following cold shock in Panstrongylus megistus (Burmeister)

The nuclear phenotypes of Malpighian tubule epithelial cells of 5th instar male nymphs of the blood-sucking insect Panstrongylus megistus were studied immediately after a short (1 h) cold shock at 0 degrees C, and 10 and 30 days later. The objective was to compare the responses to a cold shock with those known to occur after hyperthermia in order to provide insight into the cellular effect of cold in this species. Nuclei which usually exhibited a conspicuous Y chromosome chromocenter were the most frequent phenotype in control and treated specimens. Phenotypes in which the heterochromatin was unravelled, or in which there was nuclear fusion or cell death were more abundant in the shocked specimens. Most of the changes detected have also been found in heat-shocked nymphs, except for nuclear fusion which generates giant nuclei and which appeared to be less effective or necessary than that elicited after heat shock. Since other studies showed that a short cold shock does not affect the survival of more than 14% of 5th instar nymphs of P. megistus with domestic habit and can induce tolerance to a prolonged cold shock, heat shock proteins proteins are probably the best candidates for effective protection of the cells and the insects from drastic damage caused by low temperature shocks.

Survival and molting incidence after heat and cold shocks in Panstrongylus megistus Burmeister

Survival and molting incidence were studied after heat (40 degrees C) and cold (0 degree C) shocks in specimens of Panstrongylus megistus with the aim of establishing its response to temperature stress under laboratory rearing conditions and to understand occasional changes in the biological characteristics of specimens captured in nature. The response to the thermal shocks was found to vary as a function of the temperature and duration of the shock, developmental phase and sex of the specimens, and in certain cases, the insect habit and nourishment conditions. P. megistus specimens were found to be less resistant to the heat shock assay than Triatoma infestans, another reduviid species. The short cold shock affected survival of P. megistus more than did the heat shock, survival of fully-nourished specimens being preferential. The response of adults to the short cold shock was affected by sex, males being generally less resistant. The insect sylvatic habit was found to seldom affect the thermal shock response established for specimens with domestic habit. A decrease in molting frequency and sometimes a slowdown of the molting rate were found after the short heat and cold shocks, possibly promoted by change in hormonal balance, and differing from patterns reported for T. infestans. The results indicate that no generalization should be made for different reduviid species in terms of the effects of temperature shocks.

[Wild vectors of Chagas' disease in an urban area of Manaus (AM): flying activity during dry and rainy seasons]

Adults of Rhodnius prolixus, R. pictipes and Panstrongylus geniculatus found in houses in Manaus have high rates of Trypanosoma cruzi infection. Rhodnius spp. were found throughout the year, but males of P. geniculatus were significantly more frequent in the dry season.

Triatoma infestans is more efficient than Panstrongylus megistus in obtaining blood meals on non anaesthetized mice

We compared the influence of bug density in the capacity of Triatoma infestans and Panstrongylus megistus in obtaining blood meal in non anaesthetized mice. The regression analysis for increase in body weight (mg) versus density (no. of bugs/mouse) showed that in experiments with anaesthetized mice (AM), no correlation was observed. In experiments with non anaesthetized mice (NAM) the weight increase was inversely proportional to density. The regression slope for blood meal size on density was less steep for T. infestans than for P. megistus (-1.9 and -3.0, respectively). The average weight increase of P. megistus nymphs in experiments with AM was higher than for T. infestans nymphs; however, in experiments with NAM such results were inverted. Mortality of P. megistus was significantly higher than that of T. infestans with NAM. However, in experiments with AM very low mortality was observed. Considering the mortality and the slope of regression line on NAM, T. infestans is more efficient than P. megistus in obtaining blood meal in similar densities, possibly because it caused less irritation of the mice. The better exploitation of blood source of T. infestans when compared with P. megistus in similar densities, favours the maintenance of a better nutritional status in higher densities. This could explain epidemiological findings in which T. infestans not only succeeds in establishing larger colonies but also dislodges P. megistus in human dwellings when it is introduced in areas where the latter species prevails.

Possible absence of attraction to odor in Panstrongylus megistus (Hemiptera: Reduviidae) under laboratory conditions

We tested the attraction of Panstrongylus megistus odor under laboratory conditions, between males and females of this species and by individuals of each sex on recently fed virgin couples. We employed a system of choice boxes both with or without forced aeration. We observed no differences between the experimental groups with or without aeration over the stimuli in the tested situations. We also observed a clear trend among the insects to remain in the central box where they had been placed in the beginning of the tests.

[Colonization of artificial ecotopes by Panstrongylus megistus in Santa Catarina Island, Florianópolis, Santa Catarina, Brazil]

The aim of this work was to verify the colonization of Panstrongylus megistus on artificial ecotopes in Florianópolis, in the Santa Catarina Island, South Brazil. For this purpose 443 houses of the Lagoa district and 779 house annexes (524 chicken-houses, 46 corrals and 209 storage-houses) in 9 different places were examined from 1985 to 1992. These ecotopes, which include ceilings and basements, were checked after application of dislodging liquid (Pirisa 5%). Colonization by P. megistus was verified in two houses, three chicken-houses and one storage-house of the Lagoa district, where eggs, nymphs and adults were collected. To verify local reports of P. megistus occurrence, another two houses and one school were investigated. The colonization at all of these places was confirmed. In the 9 artificial ecotopes examined, 559 eggs, 305 nymphs and 24 adults were collected. The infection rate of P. megistus by Trypanosoma cruzi was 55.3% (182/329). A similar infection rate of 56.5% (78/138) was obtained in adults of P. megistus from sylvatic ecotopes and in adults captured in the houses by the inhabitants between 1983 to 1991. Precipitin tests revealed blood from just one source in 94.0% of the insects (170/181). Human blood was found in 80.6% (25/31) of the adults and in 5.8% (1/17) of the nymphs captured in the houses. These results suggest the need to ally serious epidemiologic vigilance to the effort of the inhabitants in order to avoid the risk of domiciliation of P. megistus in the houses.

Behavior of triatomines (Hemiptera:Reduviidae) vectors of Chagas' disease. IV. Fecundity, fertility and longevity of Panstrongylus megistus (Burm., 1835) pairs and virgin females starved under laboratory conditions

A laboratory study was conducted on the fecundity, fertility and life span of Panstrongylus megistus pairs and on the fecundity and life span of P. megistus virgin females submitted to starvation after the last moulting. Of the mated females, 22.2% laid eggs, 4.4% of which were fertile. Females resisted starvation more than males. Of the starved virgin females, only 10% laid eggs, with a low egg-laying rate (0.47) per female. Resistance to starvation was lower in virgin than in mated females.

Behavior of triatomines (Hemiptera: Reduviidae) vectors of Chagas' disease. III. Influence of the number of matings on the fecundity and fertility of Panstrongylus megistus (Burm., 1835) in the laboratory

A study of the effect of mating in the fecundity and fertility of females of P. megistus fed on pigeon blood every 14 days, was carried out in the laboratory. Two groups were constituted: I - females which mated only once; II - females which stayed always with the males. Only 56.7% of group I females laid fertile eggs, while as much as 90% of group II females laid fertile eggs. The duration of the fertile oviposition was greater in the females which stayed always with the males. Some females of this group were able to mate up to seven times throughout their life-span. This fact render useless sterile males in the control of these insects.

Secretory activity and endocrine regulation of male accessory glands in the blood-sucking bug Panstrongylus megistus (Hemiptera: Reduviidae)

The epithelial cells of Panstrongylus megistus male accessory glands (MAG) present ultrastructural characteristics of a secretory cell. Their secretory products are accumulated in the lumen of the four MAG lobes. During the first 8 days of adult life a strong secretion activity occurs, accumulating enough material to produce the first spermatophore. Cerebral neurosecretions as well as juvenile hormone are both involved in MAG secretory activity regulation. Juvenile hormone seems to be the responsible for the stimulation of most protein synthesis in male accessory glands. Cerebral neurosecretion seems to be necessary to stimulate juvenile hormone production and release by the corpus allatum. Furthermore, neurosecretion is required for some polypeptides synthesis by MAG. Although topic application of precocene II to adult males does not reproduce the same effects on MAG as does allatectomy, this compound causes strong reduction on male reproductive capacity.

Behavior of triatomines (Hemiptera: Reduviidae) vectors of Chagas' disease. II. Influence of feeding, lighting and time of day on the number of matings, mating speed and duration of copulation of Panstrongylus megistus (Burm, 1835) under laboratory conditions

To determine the influence of feeding, lighting and time of day on the copulating behavior of Panstrongylus megistus, 480 insect pairs were divided into four groups of 120 each and tested in the following respective situations: without food deprivation (F.D.), with five days of F.D., with ten days of F.D., and with 20 days of F.D. The tests were performed between 9:00 a.m. to 12:00 a.m. and 7:00 p.m. to 10:00 p.m., with light (700-1400 lux) and in the dark (1.4-2.8 lux) and behavior was recorded by the time sampling technique. Mating speed (MS) and duration of copulation (DC) were also calculated for each situation. The maximum frequency of copulation was observed after five days of F.D., at night, in the dark (n = 16), and the minimum was observed for recently-fed pairs, at night, with light (n = 4). Males approached females more often than females approached males. MS was lowest in pairs with twenty days of F.D., at night, with light (mean = 23.0 +/- 16.0 minutes), and highest in recently-fed pairs, during the day, with light (mean = 2.9 +/- 2.5 minutes). DC was shortest in recently-fed insects, during the day, in the dark (mean = 23.5 +/- 6.7 minutes), and longest in recently-fed animals, at night, in the dark (mean = 38.3 +/- 6.9 minutes).

Trypanosoma cruzi: kinetics of metacyclogenesis in adult and nymphal Panstrongylus megistus

Adult triatomine insects, Panstrongylus megistus, naturally infected with the protozoa, Trypanosoma cruzi, contained significantly more metacyclic trypomastigote forms in their digestive tracts than did P. megistus nymphs. Metacyclics were scarce in all stages of triatomines fed once on infected mammalian hosts and subsequently starved. In contrast, triatomines fed repeatedly on infected mammalian hosts developed prolific T. cruzi infections. Repeatedly fed adults contained 14 X more metacyclics than similarly fed nymphs. Nutritional factors appear to play a key role in regulating metacyclogenesis. Control campaigns designed to alter the age structure of populations of triatomines must take notice of the high transmission potential of the adult stage.

Host availability limits population density of Panstrongylus megistus

In order to determine whether host availability limits triatomine population growth, 5th-stage Panstrongylus megistus were maintained in feeding chambers containing 0, 1, 2, or 3 mice. During the 5-day feeding period, triatomines exposed to two or three mice gained significantly more weight than did bugs exposed to one mouse. In addition, half of the bugs exposed to two or three mice molted, as compared to one-fifth of the P. megistus exposed to one mouse. Thus, weight gain and molting were related to host density. In contrast, bug mortality was related to the triatomine-mouse ratio, being greatest among bugs exposed to one mouse. Twenty-nine nonplastered mud-stick houses in a Chagas' disease endemic area were censused and examined for triatomines. About 70% of houses with greater than or equal to 4 persons contained dense bug populations, while only 20% of houses with 1-3 persons were densely infested. Moreover, blood-meal identifications demonstrated that two-thirds of the P. megistus collected from these houses fed on man. The density of triatomines present in infested houses is related to the number of persons available as hosts.

[Changes in the level of ecdysones in the last 2 instars of Panstrongylus megistus (Heteroptera: Reduviidae)]

The ecdysone titre in the hemolymph during the two last instars of P. megistus was studied by radio-immunology technique. Changes observed are very similar in both instars. Two peaks of inequal amplitude are present. The first, always lower than the second, occurs at 1/3 of the intermoult whereas the second, distinctly higher, is observed at 2/3 period of the intermoult.

[Endocrine control of oogenesis during the fifth nymphal stage of Panstrongylus megistus (Hemiptera, Heteroptera: Reduviidae)]

Cautery of the neurosecretory cells of the pars intercerebralis, 48 hrs after feeding, of Panstrongylus megistus fifth instar, prevents the development of the ovaries, and stops the physiological processes that lead to the differentiation of oögonies into primary oöcytes.