Studies on populations of Lutzomyia longipalpis (Lutz & Neiva, 1912) (Diptera: Psychodidae: Phlebotominae) in Brazil

Studies were performed on five Brazilian populations of Lutzomyia longipalpis: Salvaterra (PA), S?o José do Ribamar (MA), Canindé (CE), Natal (RN) and Gruta da Lapinha, Lagoa Santa (MG). No morphological differences were observed that could distinguish between these populations. Homogeneity tests showed that the allopatric populations display a certain heterogeneity and that the sympatric populations, with different patterns of spots, are homogeneous. The Student-Newman-Keuls test, represented by Euler-Venn diagrams, showed a disjunction between the populations from the north/northeast and the one from Gruta da Lapinha. Genetic distances between the four populations (excluding the Canindé population) were within the range of intrapopulational differences. The Gruta da Lapinha population displayed a heterozygotic deficiency that could be a consequence of high levels of inbreeding due to cryptic habits of living in a small cave. These results do not favor the hypothesis of a L. longipalpis species complex in Brazil, and the species should be considered high polymorphic.     

Stomodaeal valve ultrastructure in the sandfly Lutzomyia longipalpis (Diptera: Psychodidae)

The stomodaeal valve and adjacent cardia region of the alimentary canal of the phlebotomine sandfly Lutzomyia longipalpis have been studied using electron microscopy. With the scanning electron microscope (SEM), numerous pit-like structures of different sizes were found in the surface of the valve of male and female flies. Under the transmission electron microscope (TEM), the cells adjacent to the pores were shown to have numerous mitochondria and to lack neural innervation. It is suggested that the pit-like structures are probably secretory. A typical basiconic sensilla was found on the inner side of the oesophagus at the junction with the stomodaeal valve, with at least one dendrite which extended to the tip, indicating a chemosensory role. It is likely that this type of sensilla may control the movement of the stomodaeal valve after contact with fluids entering the mid-gut and may be responsible for diverting the sugar meal to the crop by closure of the valve.     

Polymorphic dinucleotide microsatellite loci in the sandfly Lutzomyia longipalpis (Diptera: Phlebotominae)

The sandfly Lutzomyia longipalpis, an important vector of visceral leishmaniasis in the New World, is believed to be a species complex. In an effort to better understand population dynamics and speciation in this vector we developed a panel of dinucleotide — (CA)_n— microsatellite loci using an enrichment technique. Eleven polymorphic loci that produced consistent allelic banding patterns were characterized using a laboratory population of L. longipalpis. These dinucleotide microsatellite loci were more polymorphic than trinucleotide microsatellites characterized in wild‐caught samples of two other sandfly species; the variability of these loci was unexpected because the laboratory flies were believed to be inbred.     

Report of Lutzomyia longipalpis (Lutz & Neiva, 1912) (Diptera: Psychodidae: Phlebotominae) in a cutaneous-leishmaniasis-endemic area of Panama

Lutzomyia longipalpis is the primary vector of the parasite responsible for visceral leishmaniasis in the Americas. In the present study, Lu. longipalpis was found in a domiciliary area in Limón, a district in Capira, a region in which cutaneous leishmaniasis is endemic in Panama. Previously, this species has been found in a humid forest in this same region. Finding Lu. longipalpis in domiciliary areas indicates that this species may be adapting to new habitats and that it may play a role in the transmission of leishmaniasis in Panama.     

Navigation of Lutzomyia longipalpis (Diptera: Psychodidae) under dusk or starlight conditions

The responses of male and female Lutzomyia longipalpis (Lutz & Neiva) to different wavelengths of light was tested by presenting the sandflies with two light sources simultaneously, a series of test wavelengths between 350-670 nm and a 400 nm control. To test whether L. longipalpis could discriminate between the test and control, three sets of experiments were carried out in which the test wavelengths were presented at higher, equivalent or lower intensity than the control. In all three experiments, ultra-violet (350 nm) and blue-green-yellow (490-546 nm) light was more attractive to L. longipalpis than the control wavelength. However, at low intensity, UV was less attractive, than equivalent or higher intensity UV light. At intensities equivalent to or higher than the control wavelength, ultra-violet light was more attractive than blue-green. Furthermore, at low intensity, green-yellow (546 nm) light was more attractive to males whereas blue-green (490 nm) was more attractive to females. Blue-violet (400 nm) and orange-red (600-670 nm) light were least attractive in all three sets of experiments. Response function experiments indicated that the responses were dependent on both intensity and wavelength and that therefore more than one photoreceptor must be involved in the response. The results indicated that L. longipalpis can discriminate between different wavelengths at different intensities and thus have true colour vision. It also suggests that L. longipalpis may be able to navigate at dusk or under moonlight or starlight conditions using light in the blue-green-yellow part of the spectrum. The difference in response of males and females to light in this region is interesting and may indicate the different ecology of the sexes at night. Overall, these results may have important implications for sandfly trap design.     

Reproductive isolation between sympatric and allopatric Brazilian populations of Lutzomyia longipalpis s.l. (Diptera: Psychodidae)

Lutzomyia longipalpis s.l., the main vector of Leishmania chagasi in Latin America, is a species complex although the exact number of siblings is yet unknown. In Brazil, the siblings differ in male copulatory courtship songs and pheromones that most certainly act as pre-zygotic reproductive barriers. Here we analysed the reproductive isolation between three allopatric and two sympatric populations of Lu. longipalpis s.l. from Brazil. The results indicate a strong copulatory and pre-mating isolation between the three allopatric populations. In addition, the results also indicate a stronger pre-mating isolation between the two sympatric siblings than between the three allopatric ones, suggesting a role for reinforcement in the speciation of the Lu. longipalpis s.l. complex.     

Genetic variability among populations of Lutzomyia (Psathyromyia) shannoni (Dyar 1929) (Diptera: Psychodidae: Phlebotominae) in Colombia

Polyacrylamide gel electrophoresis was used to elucidate genetic variation at 13 isozyme loci among forest populations of Lutzomyia shannoni from three widely separated locations in Colombia: Palambí (Nari?o Department), Cimitarra (Santander Department) and Chinácota (Norte de Santander Department). These samples were compared with a laboratory colony originating from the Magdalena Valley in Central Colombia. The mean heterozygosity ranged from 16 to 22%, with 2.1 to 2.6 alleles detected per locus. Nei's genetic distances among populations were low, ranging from 0.011 to 0.049. The estimated number of migrants (Nm=3.8) based on Wright's F-Statistic, F ST, indicated low levels of gene flow among Lu. shannoni forest populations. This low level of migration indicates that the spread of stomatitis virus occurs via infected host, not by infected insect. In the colony sample of 79 individuals, the Gpi locus was homozygotic (0.62/0.62) in all females and heterozygotic (0.62/0.72) in all males. Although this phenomenon is probably a consequence of colonization, it indicates that Gpi is linked to a sex determining locus.     

Ingestion of saliva during carbohydrate feeding by Lutzomyia longipalpis (Diptera; Psychodidae)

The aim of this study was to obtain experimental evidence that phlebotomine saliva is actually ingested during the carbohydrate ingestion phase (before and after blood digestion). The ingestion of carbohydrate was simulated as it occurs in the field by offering the insects balls of cotton soaked in sucrose, sucrose crystals or orange juice cells. The results obtained here showed that ingestion occurred under each condition investigated, as indicated by the presence of apyrase, an enzyme used as a marker to detect saliva in the insect gut and/or carbohydrate sources. Saliva ingestion by phlebotomine during the carbohydrate ingestion phase is important to explain how it could promote starch digestion and to trigger Leishmania promastigotes to follow a differentiation pathway as proposed previously by some authors.     

Correlates of the peridomestic abundance of Lutzomyia longipalpis (Diptera: Psychodidae) in Amazonian Brazil

Abstract. Abundance of the sandfly Lutzomyia longipalpis , the vector of Leishmania chagasi , was surveyed using CDC light-suction traps in fifteen villages and 180 homesteads on Marajo island, Para State, Brazil. Flies were most abundant in cultivated areas, secondary growth and open woodland, away from savanna grassland and forest. Within homesteads, the abundance of flies in animal sheds was weakly associated with the number of hosts kept therein, and inversely related to the number elsewhere, both human and animal. Houses harboured more flies if dogs were present and if the house had: a roof of thatch rather than of tiles or tin; a thatched roof which had not been treated with insecticide; relatively more holes in walls and roof. The sex ratio of flies was more male-biased at higher densities. We weigh the importance of these variables as risk factors for Le.chagasi infection.     

Wing geometry as a tool for studying the Lutzomyia longipalpis (Diptera: Psychodidae) complex

Toro Toro (T) and Yungas (Y) have been described as genetically well differentiated populations of the Lutzomyia longipalpis (Lutz & Neiva, 1912) complex in Bolivia. Here we use geometric morphometrics to compare samples from these populations and new populations (Bolivia and Nicaragua), representing distant geographical origins, qualitative morphological variation ("one-spot" or "two-spots" phenotypes), ecologically distinct traits (peridomestic and silvatic populations), and possibly different epidemiological roles (transmitting or nor transmitting Leishmania chagasi). The Nicaragua (N) (Somotillo) sample was "one-spot" phenotype and a possible peridomestic vector. The Bolivian sample of the Y was also "one-spot" phenotype and a demonstrated peridomestic vector of visceral leishmaniasis (VL). The three remaining samples were silvatic, "two-spots" phenotypes. Two of them (Uyuni and T) were collected in the highlands of Bolivian where VL never has been reported. The last one (Robore, R) came from the lowlands of Bolivia, where human cases of VL are sporadically reported. The decomposition of metric variation into size and shape by geometric morphometric techniques suggests the existence of two groups (N/Y/R, and U/T). Several arguments indicate that such subdivision of Lu. longipalpis could correspond to different evolutionary units.     

Sugar feeding and fluid destination control in the phlebotomine sandfly Lutzomyia longipalpis (Diptera: Psychodidae)

Sandfly feeding behaviour and destination of coloured sugar meals in the gut of Lutzomyia longipalpis were investigated with particular attention to the role of the crop. Sandflies were able to ingest sugar from liquid drops, microcapillaries, a slice of pear and even sugar powder. In most cases the flies adopted a 'sugar feeding mode' with raised palps. As the fruit dried, flies of both sexes fed by piercing the tissue with the proboscis. All sugar-fed flies had a full crop plus a small amount of sugary fluid in the thoracic mid-gut, i.e. past the stomodaeal valve. Dissections of flies interrupted during feeding showed that the very first trace of sugar passed through the stomodaeal valve, but that the rest of the meal was diverted into the crop. This suggests that closure of the stomodaeal valve is initiated only after a small volume of sugar solution has passed through it.     

Midgut pH profile and protein digestion in the larvae of Lutzomyia longipalpis (Diptera: Psychodidae)

The sand fly Lutzomyia longipalpis is the vector of Leishmania infantum, the etiological agent of American visceral leishmaniasis. Despite its importance, until now the internal anatomy of the immature forms has never been described and little is known about their digestive processes. In nature, sand fly larvae feed on organic detritus in the soil, constantly ingesting large amounts of material. The objective of this study was to describe the anatomy of the gut and the pH of the gut lumen, as well as to investigate the proteases responsible for protein digestion. The larvae have a short gut with a prominent, well-developed midgut. Ingestion of food containing indicator dyes permitted the gut pH to be measured. A pH gradient was observed, varying from >9 in the anterior midgut to 6.5-7.0, in the posterior midgut. The endoproteolytic enzymes are secreted in the anterior midgut and are able to digest azocasein over a large pH range, specially at pH 11. Studies with various inhibitors indicated that the digestive endoproteases are trypsin- and chymotrypsin-like enzymes. These results were confirmed by using the substrates BApNA and N-CBZ-L-PpNA, specific for trypsin and chymotrypsin, respectively. Aminopeptidases were also investigated with p-nitroaniline-derived substrates. These enzymes are located in the posterior midgut, bound to the membranes and functioning at an optimal pH of 6.5-8.0. The results presented here are consistent with the current proposal that proteins are digested to peptides in the anterior midgut inside the endoperitrophic space and subsequently undergo digestion in the ectoperitrophic space of the posterior midgut.     

Host-parasite relationships of Ascogregarina chagasi (Eugregarinorida, Aseptatorina, Lecudinidae) in Lutzomyia longipalpis (Diptera: Psychodidae)

The life cycle of Ascogregarina chagasi in larvae and in adult female Lutzomyia longipalpis was studied by light and electron microscopy. Sporozoites and young gamonts were attached to the epithelial lining of the larval midgut via an osmiophilic contact zone. The mucron of young gamonts was bordered by an invaginated pellicular fold, and an electron-opaque vesicular structure was observed adjacent to it. Sporozoites possessed an apical complex and were bound by a double membrane with underlying subpellicular microtubules. The gamont pellicle was uniformly corrugated and consisted of two cortical membranes and a plasma membrane. Mature gamonts and gametocysts were found in the posterior ectoperitrophic space of third and fourth instar larval midguts and in the haemocoel of adult flies. Gametocysts in adult females adhered to the genital accessory glands, where they were encased in electron-dense capsules secreted by the fly through haemocyte-mediated humoral immune reactions. Oocytes were spindle-shaped and bound by a double-layered wall with a discernible polar plug at each end. Sporulation was endogenous, occurring within gametocysts in the midguts of larvae or the accessory glands of adult females. FITC-phalloidine staining of all stages of A. chagasi except mature gametocysts produced bright fluorescence, indicating the presence of a diffuse, actin-like protein in the cytoplasm.     

Seasonality of Lutzomyia fairtigi (Diptera: Psychodidae: Phlebotominae), a species endemic to Eastern Colombia

The bionomics of sand flies (Diptera: Phlebotominae) was studied monthly for two consecutive years in alluvial gallery forests in the department of Casanare, Northeastern Colombia. A total of 2,365 specimens and 10 species were captured using CDC light traps and Shannon traps, and from diurnal resting places, and human landing collections. Lutzomyia fairtigi Martins (55%), Lutzomyia micropyga (Mangabeira) (20.9%), and Lutzomyia antunesi (Coutinho) (13.5%) were the predominant species in the region. Lutzomyia flaviscutellata and Lutzomyia panamensis, potential vectors of Leishmania in Colombia and neighboring countries, were also collected, but in low numbers. Lu. fairtigi is an endemic species to Colombia, and minimal data are available on its biology and distribution. The present study provides additional information about Lu. fairtigi, such as the diurnal activity displayed by females on cloudy days, the greater density during the rainy season (April to October), marked anthropophilia, and the presence of flagellates in the midgut of one female.     

Activity of Lutzomyia pseudolongipalpis and L. longipalpis s.l. (Diptera: Psychodidae) in Venezuela

The nocturnal activity of the phlebotomine sandfly Lutzomyia pseudolongipalpis and two populations of L. longipalpis s.l. from different American visceral leishmaniasis foci in Venezuela was studied using collection bottle rotator traps. The activity of L. pseudolongipalpis from Lara State was continuous throughout the night, while that of L. longipalpis s.l. from El Layero, Guárico State and from Santa Ana del Valle, Margarita Island, was greatest before 23:00 h. The activity of sandflies of both populations and sexes steadily decreased thereafter. These different patterns seem to correlate with genetic data that indicate the presence in Venezuela of at least two sibling species in the L. longipalpis complex. The advantages of the bottle rotator trap for this type of study are discussed.     

Abundance of Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae) and urban transmission of visceral leishmaniasis in Campo Grande, state of Mato Grosso do Sul, Brazil

The outspread and urbanization of visceral leishmaniasis (VL) in Campo Grande, state of Mato Grosso do Sul, lead us to undertake the present study over diversity and abundance of sand flies in the urban area to compare with previous search carried out during 1999/2000, before the identification of the disease in the human population.The captures were carried out with automatic light traps, weekly, from February 2004 to February 2005 on three sites including a forested area (Zé Pereira), two peridomicilies (shelters of domestic animals and cultivation areas), and intradomicilie. In the present study 110 collections were obtained during 13 months for 1320 h of collections, resulting in 5004 specimens, 3649 males and 1355 females belonging to the 20 following species: Brumptomyia avellari, Brumptomyia sp., Bichromomyia flaviscutellata, Evandromyia lenti, E. termitophila, E. cortelezzii, E. borrouli, Lutzomyia sp., L. longipalpis, Micropygomyia quinquefer, N. antunesi, N. whitmani, Pintomyia christenseni, Pi. damascenoi, Psathyromyia aragaoi, Ps. campograndensis, Ps. hermanlenti, Ps. shannoni, Pychodopygus claustrei, and Sciopemyia sordellii. L. longipalpis was the most abundant species in the anthropic environment with 92.22% of the captures. This shows an increase of sixty times in the density of L. longipalpis compared to the last sand fly evaluation in 1999/2000. The high density of L. longipalpis in Campo Grande is the main factor of risk in transmission of the disease to human in the urban area. The capture of N. antunesi, typical specie from Amazonian region, in Mato Grosso do Sul is reported for the first time.