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Richard C Wilkerson

Publications and source records attributed to Richard C Wilkerson.

11 recordsLinked to original sources
PubMed2006

Intragenomic rDNA ITS2 variation in the neotropical Anopheles (Nyssorhynchus) albitarsis complex (Diptera: Culicidae).

We cloned and sequenced the rDNA internal transcribed spacer 2 (ITS2) of 4 species belonging to the neotropical Anopheles (Nyssorhynchus) albitarsis complex, that is, A. albitarsis; A. albitarsis B; Anopheles marajoara, a proven malaria vector; and Anopheles deaneorum, a suspected vector. Even though the ITS2 sequences of these species were very similar (< or =1.17% divergence), we found differences suitable for species identification and intragenomic variation of possible consequence in phylogenetic reconstruction. Variation came from 2 microsatellite regions and a number of indels and base substitutions. The existence of partially correlated subsets of clones in A. albitarsis is hypothesized either to be separate rDNA loci or to be semi-independently evolving portions of a single rDNA locus. No differences were found between males and females, suggesting that similar rDNA arrays exist on both the X and Y chromosomes. In addition, highly variant clones, possibly pseudogenes, were found in A. marajoara from Venezuela.

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PubMed2006

Ecology of the malaria vector, Anopheles (Nyssorhynchus) marajoara Galvão and Damasceno in Trinidad, West Indies.

The taxonomy and ecology of wild-caught Anopheles marajoara mosquitoes derived from rice fields in Frederick Settlement, Trinidad, were studied in the laboratory using specimens identified with species-specific random amplified polymorphic DNA (RAPD) profiles and recently developed rDNA ITS2 polymerase chain reaction methods. Adults were collected using Shannon traps and human bait in 2 houses over a 1-year period. All mosquitoes collected were taken to the laboratory, where they were identified, wing-length measured, and parity rates determined using standard methods. In addition, 25 females were blood fed and subsequently offered a blood meal every 2 h for a 60-h period. Based on the morphological keys and molecular tools used, the presence of An. marajoara is confirmed in Trinidad for the first time. Analysis of the seasonal distribution of An. marajoara revealed that over 58% were collected during the rainy season. The wing length of 660 females measured averaged 2.90 +/- 0.130 mm, with no significant differences being observed among the parous and nulliparous females' wing sizes (2.90 and 2.92 mm, respectively). In addition, the monthly parous rate was not significantly correlated with mean wing-length over time (r = 0.157, df = 16, P > 0.07). Results from the blood feeding studies showed 85% of females blood fed immediately (hour 0) after capture in the field. However, blood feeding declined thereafter until 24 h later, when over 40% refed. This study clearly identified the presence of An. marajoara in Trinidad and provides information of the seasonal abundance and blood-feeding behaviors. These results suggest that this species can play a significant role in the transmission of malaria within its geographical range in the Neotropics.

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PubMed2006

Pathways of expansion and multiple introductions illustrated by large genetic differentiation among worldwide populations of the southern house mosquito.

The southern house mosquito Culex quinquefasciatus is a principal vector of human lymphatic filariasis, several encephalitides (including West Nile virus), avian malaria, and poxvirus, but its importance as a vector varies considerably among regions. This species has spread with humans and is ubiquitous in tropical urban and suburban environments. This was the first mosquito to reach Hawaii and we performed a worldwide genetic survey using micro-satellite loci to identify its source. Our analyses showed divergent Old World and New World genetic signatures in Cx. quinquefasciatus with further distinctions between east and west African, Asian, and Pacific populations that correlate with the epidemiology of human filariasis. We found that in Hawaii south Pacific mosquitoes have largely replaced the original New World introduction of Cx. quinquefasciatus, consistent with their reported expansion to higher elevations. We hypothesize worldwide pathways of expansion of this disease vector.

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PubMed2006

Population structure of the malaria vector Anopheles darlingi in a malaria-endemic region of eastern Amazonian Brazil.

Anopheles darlingi is the primary malaria vector in Latin America, and is especially important in Amazonian Brazil. Historically, control efforts have been focused on indoor house spraying using a variety of insecticides, but since the mid-1990s there has been a shift to patient treatment and focal insecticide fogging. Anopheles darlingi was believed to have been significantly reduced in a gold-mining community, Peixoto de Azevedo (in Mato Grosso State), in the early 1990s by insecticide use during a severe malaria epidemic. In contrast, although An. darlingi was eradicated from some districts of the city of Belem (the capital of Para State) in 1968 to reduce malaria, populations around the water protection area in the eastern district were treated only briefly. To investigate the population structure of An. darlingi including evidence for a population bottleneck in Peixoto, we analyzed eight microsatellite loci of 256 individuals from seven locations in Brazil: three in Amapa State, three in Para State, and one in Mato Grosso State. Allelic diversity and mean expected heterozygosity were high for all populations (mean number alleles/locus and H(E) were 13.5 and 0.834, respectively) and did not differ significantly between locations. Significant heterozygote deficits were associated with linkage disequilibrium, most likely due to either the Wahlund effect or selection. We found no evidence for a population bottleneck in Peixoto, possibly because the reduction was not extreme enough to be detected. Overall estimates of long-term N(e) varied from 92.4 individuals under the linkage disequilibrium model to infinity under the heterozygote excess model. Fixation indices and analysis of molecular variance demonstrated significant differentiation between locations north and south of the Amazon River, suggesting a degree of genetic isolation between them, attributed to isolation by distance.

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PubMed2005

Identification of Anopheles (Nyssorhynchus) albitarsis complex species (Diptera: Culicidae) using rDNA internal transcribed spacer 2-based polymerase chain reaction primes.

Anopheles (Nyssorhynchus) marajoara is a proven primary vector of malaria parasites in Northeast Brazil, and An. deaneorum is a suspected vector in Western Brazil. Both are members of the morphologically similar Albitarsis Complex, which also includes An. albitarsis and an undescribed species, An. albitarsis "B". These four species were recognized and can be identified using random amplified polymorphic DNA (RAPD) markers, but various other methodologies also point to multiple species under the name An. albitarsis. We describe here a technique for identification of these species employing polymerase chain reaction (PCR) primers based on ribosomal DNA internal transcribed spacer 2 (rDNA ITS2) sequence. Since this method is based on known sequence it is simpler than the sometimes problematical RAPD-PCR. Primers were tested on samples previously identified using RAPD markers with complete correlation.

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PubMed2005

Anopheles triannulatus (Neiva and Pinto): a new Anopheles record from Trinidad, West Indies.

We report the first collection of Anopheles triannulatus from Trinidad, West Indies. Adults were captured using human bait while larvae and pupae were collected from a pond located in Valencia, north Trinidad. The associated species was An. oswaldoi. This new record increases the number of mosquito species belonging to the Genus Anopheles to 14 and the total species count from 162 to 163 in Trinidad, West Indies.

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PubMed2005

Habitats and distribution of Anopheles sinensis and associated Anopheles hyrcanus group in Japan.

Mosquito collections were carried out in August 2002 and July 2003 in Japan. Anopheles sinensis of the Hyrcanus Group, Myzomyia Series of Anopheles, was the most common species encountered. The distribution and habitats of 5 Anopheles Hyrcanus Group species are included. Eight species belonging to Aedes, Culex, and Uranotaenia were found associated with An. sinensis in rice paddies and a variety of other larval habitats.

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PubMed2004

Emerging vectors in the Culex pipiens complex.

In the Old World, some mosquitoes in the Culex pipiens complex are excellent enzootic vectors of West Nile virus, circulating the virus among birds, whereas others bite mainly humans and other mammals. Here we show that, in northern Europe, such forms differing in behavior and physiology have unique microsatellite fingerprints with no evidence of gene flow between them, as would be expected from distinct species. In the United States, however, hybrids between these forms are ubiquitous. Such hybrids between human-biters and bird-biters may be the bridge vectors contributing to the unprecedented severity and range of the West Nile virus epidemic in North America.

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PubMed2004

Ribosomal DNA ITS2 sequences differentiate six species in the Anopheles crucians complex (Diptera: Culicidae).

Anopheles crucians Wiedemann (sensu lato) was investigated for the presence of cryptic species using rDNA ITS2 sequences. This complex of species presently contains the named species An. crucians, An. bradleyi King, and An. georgianus King. Adult female mosquitoes were collected at 28 sites in Alabama, Florida, Georgia, North Carolina, Mississippi, and Louisiana, resulting in 245 progeny broods. Species were identified using preliminary morphological characters, and the internal transcribed spacer two (ITS2) was amplified from all broods. The result was five distinct sizes of amplification product, and based on morphological characters, one of the size classes was suspected to consist of two species. All six putative species were then sequenced: five directly, and the sixth, because of extreme intragenomic (each individual with many variants) size variability, cloned. The ITS2 sequences were markedly distinct for all six species. Species designations and ITS2 sequence lengths (base pairs in parentheses) were A (461), B (1,000+), C (204), D (293), E (195), and An. bradleyi (208). Species B showed both large intraspecific and intragenomic sequence variability and is distinguished by having the longest ITS2 found so far in an Anopheles. Based on these data, we found that all species could be identified with polymerase chain reaction (PCR) using a mixture of four primers in a single reaction. Members of this complex were often found in sympatry, with the adults of five species collected at a single site in central Florida.

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PubMed2002

Emergence of a new neotropical malaria vector facilitated by human migration and changes in land use.

In a region of northeastern Amazonia, we find a species previously of minor importance, Anopheles marajoara, to be the principal malaria vector. In a total of five collections during 1996-97 in three replicated sites near the city of Macapá, Amapá state, this species occurs in much greater abundance compared with the presumed vector Anopheles darlingi. Also, a significantly higher proportion of An. marajoara is infected with malaria parasites, determined by the ELISA technique. This appears to be the result of increased abundance of An. marajoara due to alterations in land use, invasion of its primary breeding sites by human immigrants, and its anthropophilic behavior. This discovery highlights one of the challenges of Neotropical malaria control, namely that the targeting of specific vectors may be complicated by a changing mosaic of different locally important vectors and their interactions with human populations.

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