Lutzomyia Vexator Research Articles

Genetic differentiation over a small spatial scale of the sand fly Lutzomyia vexator (Diptera: Psychodidae)

BackgroundThe geographic scale and degree of genetic differentiation for arthropod vectors that transmit parasites play an important role in the distribution, prevalence and coevolution of pathogens of human and wildlife significance. We determined the genetic diversity and population structure of the sand fly Lutzomyia vexator over spatial scales from 0.56 to 3.79 km at a study region in northern California. The study was provoked by observations of differentiation at fine spatial scales of a lizard malaria parasite vectored by Lu. vexator.MethodsA microsatellite enrichment/next-generation sequencing protocol was used to identify variable microsatellite loci within the genome of Lu. vexator. Alleles present at these loci were examined in four populations of Lu. vexator in Hopland, CA. Population differentiation was assessed using Fst and D (of Cavalli-Sforza and Edwards), and the program Structure was used to determine the degree of subdivision present. The effective population size for the sand fly populations was also calculated.ResultsEight microsatellite markers were characterized and revealed high genetic diversity (uHe = 0.79–0.92, Na = 12–24) and slight but significant differentiation across the fine spatial scale examined (average pairwise D = 0.327; F ST = 0.0185 (95 % bootstrapped CI: 0.0102–0.0264). Even though the insects are difficult to capture using standard methods, the estimated population size was thousands per local site.ConclusionsThe results argue that Lu. vexator at the study sites are abundant and not highly mobile, which may influence the overall transmission dynamics of the lizard malaria parasite, Plasmodium mexicanum, and other parasites transmitted by this species.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1826-5) contains supplementary material, which is available to authorized users.

Discrimination of the Plasmodium mexicanum vectors Lutzomyia stewarti and Lutzomyia vexator by a PCR-RFLP assay and Wolbachia infection.

Lutzomyia vexator (Coquillett 1907) and L. stewarti (Mangabeira Fo & Galindo 1944), are two of the fourteen reported species of sand flies (Diptera: Psychodidae) inhabiting North America (Young and Perkins 1984). These two species are found in sympatry in California (Ayala 1973, Young and Perkins 1984), and often occupy the same rodent burrows for resting sites. Both species transmit the saurian malaria parasite, Plasmodium mexicanum, to lizards in northern California (Ayala, 1973, Schall 2000, Vardo-Zalik 2009). Additionally, these flies have been documented as hosts for other reptilian pathogens, including trypanosomes, haemogregarines, and gregarines (Ayala 1973). Therefore, knowledge of these vectors is important for understanding reptilian disease ecology. Lutzomyia vexator has also been implicated as a potential vector for canine leishmaniasis after being found in upstate New York proximal to a canine leishmanisis outbreak (Ostfeldt et al. 2004).

Current and future niche of North and Central American sand flies (Diptera: psychodidae) in climate change scenarios.

Ecological niche models are useful tools to infer potential spatial and temporal distributions in vector species and to measure epidemiological risk for infectious diseases such as the Leishmaniases. The ecological niche of 28 North and Central American sand fly species, including those with epidemiological relevance, can be used to analyze the vector's ecology and its association with transmission risk, and plan integrated regional vector surveillance and control programs. In this study, we model the environmental requirements of the principal North and Central American phlebotomine species and analyze three niche characteristics over future climate change scenarios: i) potential change in niche breadth, ii) direction and magnitude of niche centroid shifts, iii) shifts in elevation range. Niche identity between confirmed or incriminated Leishmania vector sand flies in Mexico, and human cases were analyzed. Niche models were constructed using sand fly occurrence datapoints from Canada, USA, Mexico, Guatemala and Belize. Nine non-correlated bioclimatic and four topographic data layers were used as niche components using GARP in OpenModeller. Both B2 and A2 climate change scenarios were used with two general circulation models for each scenario (CSIRO and HadCM3), for 2020, 2050 and 2080. There was an increase in niche breadth to 2080 in both scenarios for all species with the exception of Lutzomyia vexator. The principal direction of niche centroid displacement was to the northwest (64%), while the elevation range decreased greatest for tropical, and least for broad-range species. Lutzomyia cruciata is the only epidemiologically important species with high niche identity with that of Leishmania spp. in Mexico. Continued landscape modification in future climate change will provide an increased opportunity for the geographic expansion of NCA sand flys' ENM and human exposure to vectors of Leishmaniases.

Virulence of a Malaria Parasite, Plasmodium mexicanum, for Its Sand Fly Vectors, Lutzomyia vexator and Lutzomyia stewarti (Diptera: Psychodidae)

Evolutionary theory predicts that virulence of parasites for mobile vector insects will be low for natural parasite-host associations that have coevolved. I determined virulence of the malaria parasite of lizards, Plasmodium mexicanum, for its vectors, two species of sand fly (Diptera: Psychodidae), Lutzomyia vexator (Coquillett 1907) and Lutzomyia stewarti (Mangabeira Fo & Galindo 1944), by measuring several life history traits. Developmental rate from egg to eclosion differed for the two species when noninfected. For both sand fly species, developmental rate for each stage (egg to larval hatching, larval period, pupal period) and life span were not altered by infection. Infected sand flies, however, produced fewer eggs. This reduction in fecundity may be a result of lower quality of the blood meal taken from infected lizards (lower concentration of hemoglobin). This report is the first measure of virulence of Plasmodium for an insect vector other than a mosquito and concords with both expectations of theory and previous studies on natural parasite-host associations that revealed low virulence.

Investigation of Habitat Effects on the Spatial Distribution of Lutzomyia shannoni Across Heterogeneous Environments, With Note of Respective Mosquito Species Compositions

Sand flies are small blood feeding dipterans that are primary vectors of numerous human and livestock pathogens. Control efforts are often complex and multidimensional. A fundamental step in the development and implementation of any integrated pest management (IPM) program is the refining of effective surveillance and identification techniques. Before this study, the presence of two species, Lutzomyia shannoni (Dyar) and Lutzomyia vexator (Coquillett) became known in Kentucky and surrounding states. To understand the spatial distribution of these species across heterogeneous landscapes in this region, trapping was conducted at random locations in previously designated habitats. Although a lack of clear data prevented any conclusions to be drawn for the preferences of L. vexator, the species of greater medical and veterinary importance, L. shannoni, was documented to show a strong preference for habitats along the wooded edges of pasture lands. In the region of study, these lands are frequently used in the production of beef cattle and other livestock, reinforcing the veterinary significance of the findings. Because of their familiarity to vector control officials and operators, mosquito species compositions were compared with the recorded abundance of L. shannoni across the varied habitats. The linking of this information should prove useful to management plans for the phlebotomine, if warranted in the future.

The Seasonal Abundance of Phlebotomine Sand Flies, Lutzomyia Species in Florida

The seasonality of phlebotomine sand flies was studied in Florida, utilizing colored light-emitting diode- and attractant-baited Mosquito Magnet MM-X traps from September 2006 to September 2008 at San Felasco Hammock Preserve State Park, Gainesville, FL. A total of 6,278 sand flies were collected from 314 actual nights and 1,692 total trap-nights, yielding 3.7 sand flies per trap-night. Lutzomyia shannoni was the predominant species, constituting 55% to 80% of the total sand fly populations collected during the studies. Both L. shannoni and L. vexator populations were highly seasonal and were moderately influenced by weather factors. Lutzomyia shannoni populations peaked in May and showed reduced activity during December, January, and February. This species was active throughout the year and showed positive and negative correlations with average monthly temperature and relative humidity, respectively. Lutzomyia vexator showed peak activity during August and October with an activity lull from December to March. This species showed a positive correlation with average monthly temperature. No correlations were observed with either species for average daily, weekly, or 1- to 8-wk-lagging precipitation, number of rainy days, wind speed, or lunar phases. Lutzomyia shannoni abundance was weakly correlated to L. vexator abundance. No other Lutzomyia spp. were collected during the study.

Lutzomyiaspp. (Diptera: Psychodidae) Response to Olfactory Attractant- and Light Emitting Diode-Modified Mosquito Magnet X (MM-X) Traps

Mosquito Magnet-X traps were modified for use with blue, green, red, and blue-green-red light-emitting diodes and olfactory attractants to determine the response of Lutzomyia shannoni (Dyar) and Lutzomyia vexator (Coquillett) (Diptera: Psychodidae) field populations to these attractants. Red and blue-green-red-baited traps captured the highest numbers of Lu. shannoni and Lu. vexator, respectively, although, there were no significant differences between the colors. Baiting the traps with CO, attracted significantly higher numbers of Lu. shannoni but showed no effect on Lu. vexator capture. In comparison with CO, alone, Lu. shannoni preferred 1-octen-3-ol and 1-hexen-3-ol (0.05 g per trap) in combination with CO.

New State Records for <I>Lutzomyia shannoni</I> and <I>Lutzomyia vexator</I>

Two species of phlebotomine sand flies, Lutzomyia shannoni (Dyar) and Lutzomyia vexator (Coquillett), are reported for the first time from Kentucky and Ohio. L. vexator also is reported for the first time from Tennessee. These insects were found in a northeasterly band extending from southwestern Kentucky to southwestern Ohio. Both species were consistently captured from mid-July through September in 2006 and 2007 by using CO2-baited Center for Disease Control light traps. Weekly sampling revealed that these flies are more abundant in the southern part of this band than in the northern part, but increasing densities throughout this new range indicate that the flies are currently expanding their range. Although both species have been reported further north along the Atlantic coast, and L. vexator along the Pacific coast, neither of them had been reported this far north along the Mississippi Valley. Previous reports established L. shannoni as far north as west central Tennessee and L. vexator in a similar spatial pattern in the eastern part of its range, extending as far north as northern Alabama. Whether the new records reported herein represent a northerly expansion of the geographic range of these species or are reflective of sampling changes is inconclusive. However, the former scenario could presage an increased prevalence of the diseases associated with this group of insects.

Clonal diversity of a malaria parasite, Plasmodium mexicanum, and its transmission success from its vertebrate-to-insect host

Infections of the lizard malaria parasite Plasmodium mexicanum are often genetically complex within their fence lizard host ( Sceloporus occidentalis) harbouring two or more clones of parasite. The role of clonal diversity in transmission success was studied for P. mexicanum by feeding its sandfly vectors ( Lutzomyia vexator and Lutzomyia stewarti) on experimentally infected lizards. Experimental infections consisted of one, two, three or more clones, assessed using three microsatellite markers. After 5 days, vectors were dissected to assess infection status, oocyst burden and genetic composition of the oocysts. A high proportion (92%) of sandflies became infected and carried high oocyst burdens (mean of 56 oocysts) with no influence of clonal diversity on these two measures of transmission success. Gametocytemia was positively correlated with transmission success and the more common vector ( L. vexator) developed more oocysts on midguts. A high proportion (∼74%) of all alleles detected in the lizard blood was found in infected vectors. The relative proportion of clones within mixed infections, determined by peak heights on pherograms produced by the genetic analyser instrument, was very similar for the lizard’s blood and infections in the vectors. These results demonstrate that P. mexicanum achieves high transmission success, with most clones making the transition from vertebrate-to-insect host, and thus explains in part the high genetic diversity of the parasite among all hosts at the study site.

Sand fly (Lutzomyia vexator) (Diptera: Psychodidae) populations in upstate New York: abundance, microhabitat, and phenology.

Visceral leishmaniasis is an endemic protozoal disease of humans and dogs in tropical and subtropical regions in Asia, Africa, southern Europe, Central America, and South America, where sand flies (genera Phlebotomus and Lutzomyia) act as vectors. An outbreak in a New York foxhound kennel and subsequent surveillance revealed widespread Leishmania infantum infection of dogs in the United States, outside the known range of the vector sand flies. For this study, we conducted surveillance for sand flies during the summers of 2001 and 2002 at two areas: on the grounds of the New York kennel and at the Institute of Ecosystem Studies (IES) 10 km away. CO2-baited light traps were used for surveillance. Populations of Lutzomyia vexator, not previously known in New York, were widespread and locally abundant (range, 0.26-1.16 flies/trap night) at the IES site. These populations showed a bimodal, midsummer activity peak and were most abundant on steep slopes within mature mixed hardwood forests. Further research will be necessary to determine whether the New York populations of L. vexator in the vicinity of the kennel could be involved in transmission of canine leishmaniasis.

Transmission success of the malaria parasite Plasmodium mexicanum into its vector: role of gametocyte density and sex ratio.

The life-cycle of Plasmodium depends on transmission of the parasite from the vertebrate host into its vector when the insect takes a bloodmeal. Transmission success may depend in part on the parasite's gametocyte density and sex ratio in the blood. P. mexicanum, a parasite of fence lizards in California, USA, exploits the sandfly Lutzomyia vexator as its vector. In experimental transmissions using naturally infected lizards as donors of blood, transmission success (measured as percentage of vectors infected and number of parasite oocysts on the insect's midgut) was positively related to gametocyte density, although density above 20/1000 erythrocytes did not improve transmission. Sex ratio (proportion of microgametocytes in the infection) was positively correlated with gametocyte density. Transmission improved with higher proportion of microgametocytes, but partial correlations revealed that this was a result only of higher gametocyte densities. These results agree with the theory of virulence and sex ratios because single clone infections should produce a more female-biased sex ratio and grow to the minimum parasitaemia that would maximize clonal transmission, whereas multiple clone infections will be closer to a 1:1 sex ratio and yield a higher parasitaemia when each clone competes for transmission to the vector.

Thermal Ecology of a Malarial Parasite and its Insect Vector: Consequences for the Parasite's Transmission Success

We examined the transmission biology of Plasmodium mexicanum, a parasite of the fence lizard Sceloporus occidentalis, and its vector, the sandfly Lutzomyia vexator. Female L. vexator produced a clutch of eggs after each blood meal taken from a lizard. Mortality was high after oviposition, so few sandflies were likely to take two blood meals and almost none took three. Therefore, to maximize its transmission success, the parasite must complete development in its insect host before the vector lays its eggs and takes another blood meal. Between 16°C and 32°C, temperature did not affect the longevity of female sandflies, but did affect the rate of parasite development in the insect, the rate of maturation of sandflies' eggs, and the probability of sandflies becoming infected. The above relationships with temperature were non-linear and differed in shape among the variables such that an increase in temperature between 22°C and 32°C benefited the parasite by shortening its development while not reducing the time until the sandfly's next blood meal. We measured the temperatures available to the vectors in nature (burrows of ground squirrels). Within this range, there was a window that allowed successful transmission of the parasite (based on laboratory studies). In a thermal gradient, unfed female sandflies selected mean temperatures approximately 4°C below the minimum required for transmission. After a blood meal from a non-infected lizard, the insect's mean preferred temperature increased 1.6°C, presumably to aid digestion, and if a blood meal was taken from an infected lizard mean preferred body temperature increased by 3.6°C. Compared with 10 other Plasmodium species, P. mexicanum has a very rapid rate of development in its vector. The results suggest P. mexicanum enhances its transmission success through a combination of rapid development in the insect host and manipulation of the vector's thermoregulatory behaviour.

Development and experimental transmission of Schellackia golvani and Schellackia occidentalis by ingestion of infected blood-feeding arthropods

Klein T. A., Young D. G., Greiner E. G., Telford S. R., Jr and Butler J.F. 1988. Development and experimental transmission of Schellackia golvani and Schellackia occidentalis by ingestion of infected blood-feeding arthropods. International Journal for Parasitology 18: 259–267. Experimental transmission of Schellackia parasites was accomplished by ingestion of mosquitoes, phlebotomine sand flies, and mites that had fed previously on their respective, infected, natural hosts, i.e. Schellackia golvani transmission to Anolis carolinensis and Schellackia occidentalis to Sceloporus undulatus. Attempts to transmit S. golvani to Sc. undulatus and S. occidentalis to A. carolinensis were unsuccessful, thus demonstrating their specific differentiation. The prepatent period was reduced significantly when temperatures were elevated for both Schellackia species, i.e. >20 days at 18–24°C decreased to 7–12 days at 32°C. Sporozoites of S. golvani ingested by sand flies and mosquitoes during blood-feeding invaded the intestinal epithelial cells where they remained quiescent in a parasitophorus vacuole. Sand flies ( Lutzomyia vexator) were infective for up to 7 days after the blood meal on lizards infected with either S. golvani or S. occidentalis. Mosquitoes ( Culex erraticus) were infective for up to 29 days after a blood meal on A. carolinensis infected with S. golvani. Histological preparations of A. carolinensis infected with S. golvani and Sc. undulatus infected with S. occidentalis revealed schizogony occurring in the intestinal epithelial cells; gametogony and sporogony occurred in the lamina propria of the the small intestine. The evidence presented strengthens the supposition that haematophagous dipterans rather than geckobiid mites, as earlier reported, are more important natural vectors of Schellackia species.

Ultrastructural Comparison of Egg Surface Morphology of Five Lutzomyia Species (Diptera: Psychodidae)

Surface structure of sand fly eggs of five species are illustrated with scanning electron micrographs. Eggs studied were from the following New World sand fly species: Lutzomyia anthophora (Addis), Lutzomyia cruciata (Coquillett), Lutzomyia diabolica (Hall), Lutzomyia shannoni (Dyar), and Lutzomyia vexator (Coquillett). Eggs of these five species and of 36 previously described species were grouped into four morphological categories based on egg surface patterns: polygonal, connected parallel ridges, unconnected parallel ridges, and volcanolike. Several methods used for fixation of sand fly eggs are discussed.