Entomological assessment in 'hotspots' of four lymphatic filariasis endemic districts, Central Nepal during post-MDA surveillance.

BACKGROUND OBJECTIVES: Annual mass drug administration (MDA) is the main strategy to interrupt the transmission of lymphatic filariasis (LF) in the community. The main aim of monitoring the MDA program, for its effectiveness and interruption of LF is the post-MDA surveillance using antigen survey in children born after MDA. The latest technique of new research suggests that xenomonitoring is an effective tool for monitoring LF intervention. The objective of this study was to assess the W. bancrofti infection/or infectivity in vector mosquitoes by xenomonitoring during post-MDA surveillance. METHODS: A descriptive cross-sectional study was conducted in the hotspots of selected four districts of Central Nepal. A gravid trap technique was used for sampling mosquitoes. Infection/or infectivity was determined via the dissection of vector mosquitoes. Anopheles, Aedes, Armigerus and Culex species were collected from hotspots of four endemic districts, two from the hilly region (Lalitpur and Dhading) and two from Terai region (Bara and Mahottari) of Central Nepal. RESULTS: A total of 4450 mosquitoes belonging to four genera, Anopheles, Culex, Armigeres, and Aedes were collected from four hotspots. The distribution of Culex quinquefasciatus was found to be the highest, 88.9% (n=3955/4450) followed by Cx. vishnui (4.5%), Armigeres sp (5.8%), An. culicifascies (0.2%), Aedes spp (0.8%). The proportion of female mosquitoes trapped is significantly higher. A total of 3344 parous Cx. quinquefasciatus mosquitoes were dissected for any larval stage of W. bancrofti. We could not find any filarial infection in dissected mosquito samples. INTERPRETATION CONCLUSION: We conclude that the gravid trap is an efficient tool for the collection of gravid Cx. quinquefasciatus mosquitoes for xenomonitoring studies of filariasis endemic regions. Vector composition indicated a maximum number of vector mosquitoes of lymphatic filariasis were trapped compared with the other three species. Distribution and density of Cx. quinquefasciatus was found highest in four hotspots of endemic districts. None of the Cx. quinquefasciatus dissected were found to be infected by larval forms of filaria. Since the low levels of infection persistence in the human population in these hot spots, vector infection and infectivity can't be ignored. Microscopic xenomonitoring at a low level of infection persistent is less likely to be efficient so molecular xenomonitoring along with a large sample should be required in each of the hot spots of the districts. Additionally, area is receptive so further vector control intervention should be required to reduce the risk of resurgence of infection.

Assessment of Truck-Mounted Area-Wide S-methoprene Applications to Manage West Nile Virus Vector Species in the Suburbs of Chicago, IL, USA.

West Nile virus remains the leading cause of arboviral neuroinvasive disease in the United States, despite extensive efforts to control the mosquito vectors involved in transmission. In this study, we evaluated the effectiveness of Altosid SR-20 (active ingredient, S-methoprene 20%) larvicide applications using truck-mounted ultra-low volume (ULV) dispersal equipment to target Culex pipiens Linnaeus (Diptera: Culicidae) and Cx. restuans (Theobald)larvae. A combination of emergence bioassays, open-field measurements of deposited S-methoprene and spray distribution using gas chromatography-mass spectrometry, and assessments of adult Culex spp. populations in response to applications were conducted over the summer of 2020 within the North Shore Mosquito Abatement District (IL, USA). Open-field applications revealed that dispersed Altosid SR-20 using ULV equipment was effective (75% emergence inhibition in susceptible lab strain Cx. pipiens larvae) up to 53 m. In suburban neighborhood applications, we found that S-methoprene deposition and larval emergence inhibition (EI) in front yards did not differ significantly from backyards. An overall EI of 46% and 28% were observed for laboratory strain Cx. pipiens and wild Cx. restuans larvae respectively, and both had an EI significantly higher than the untreated control group. The EI of exposed wild Cx. pipiens larvae did not differ from the untreated controls, suggesting an increased tolerance to S-methoprene. No difference in abundance of gravid or host-seeking adult Culex spp. post-application was detected between treated and untreated sites. These results document the ability of area-wide application to distribute S-methoprene, but this strategy will need further modifications and evaluation for Culex spp. management.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit.

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Artificial blood feeding for Culicidae colony maintenance in laboratories: does the blood source condition matter?

Culicidae colonization in laboratory is paramount to conduct studies aiming at a better understanding of mosquitoes' capacity to transmit pathogens that cause deadly diseases. Colonization requires female blood feeding, a necessary step for maturation of female's oocytes. Direct blood feeding on anesthetized mammals implies in a number of disadvantages when compared to artificial blood feeding. Consequently, laboratories worldwide have been trying to -feed female mosquitoes artificially in order to replace direct feeding. In this study, we compared the effects of direct blood feeding and artificial blood feeding on important life traits of three Culicidae species. Artificial feeding was performed using citrated or defibrinated sheep blood and citrated or defibrinated rabbit blood. Direct feeding was performed using anesthetized guinea pigs as the blood source and the experiment control. Results indicated that artificial feeding using sheep blood was not good enough to justify its use in the maintenance of laboratory colonies of Culicidae. However, artificial feeding using rabbit blood maintained a recovery rate always very close to the control, especially when blood was citrated. We concluded that artificial feeding using citrated rabbit blood can substitute direct feeding on mammals reducing the use of animals, eliminating the need to maintain a bioterium in the laboratory and reducing costs in scientific researches involving Culicidae vectors.

Molecular xenomonitoring for Wuchereria bancrofti in Culex quinquefasciatus in two districts in Bangladesh supports transmission assessment survey findings.

BACKGROUND: Careful monitoring for recrudescence of Wuchereria bancrofti infection is necessary in communities where mass drug administration (MDA) for the elimination of lymphatic filariasis (LF) as a public health problem has been stopped. During the post-MDA period, transmission assessment surveys (TAS) are recommended by the World Health Organization to monitor the presence of the parasite in humans. Molecular xenomonitoring (MX), a method by which parasite infection in the mosquito population is monitored, has also been proposed as a sensitive method to determine whether the parasite is still present in the human population. The aim of this study was to conduct an MX evaluation in two areas of Bangladesh, one previously endemic district that had stopped MDA (Panchagarh), and part of a non-endemic district (Gaibandha) that borders the district where transmission was most recently recorded. METHODOLOGY/PRINCIPAL FINDINGS: Mosquitoes were systematically collected from 180 trap sites per district and mosquito pools were tested for W. bancrofti using real-time PCR. A total of 23,436 intact mosquitoes, representing 31 species, were collected from the two districts, of which 10,344 (41%) were Culex quinquefasciatus, the vector of W. bancrofti in Bangladesh. All of the 594 pools of Cx. quinquefasciatus tested by real-time PCR were negative for the presence of W. bancrofti DNA. CONCLUSIONS/SIGNIFICANCE: This study suggested the absence of W. bancrofti in these districts. MX could be a sensitive tool to confirm interruption of LF transmission in areas considered at higher risk of recrudescence, particularly in countries like Bangladesh where entomological and laboratory capacity to perform MX is available.

Entomological assessment of yellow fever-epidemic risk indices in Benue State, Nigeria, 2010-2011.

Yellow fever (YF) is a vector-borne disease affecting humans and non-human primates in tropical areas. In the past, there have been pockets of YF outbreaks in Nigeria that resulted in preventable deaths. Surveillance efforts towards avoiding another outbreak have been put in place with the aim of early detection and control. However, risk indices relating to the density of immature YF-mosquito vectors are given little consideration even though it is the first step in curbing a possible outbreak. Immature collections from 1538 houses in Ega, Oju, Otukpoicho and Otukpo in Benue State were carried out in 2010 and 2011. Risk indices such as house index (HI), container index (CI) and Breteau index (BI) were estimated. Molecular detection of YF was carried out on randomly selected Aedes larvae and pupae. Overall, 431,381 mosquitoes were collected in and around house premises. Thirteen species were identified: Ae. aegypti (Linneaus), Ae. africanus (Theobald), Ae. albopictus (Skuse), Ae. cumminsii (Theobald), Ae. luteocephalus (Newstead), Ae. simpsoni s.l. (Theobald), Ae. vittatus (Bigot), Anopheles gambiae Giles, An. nili (Theobald), Cx. nebulosus Theobald, Culex quinquefasciatus Say, Lutzia tigripes (Grandpre and Charmoy) and Toxorhynchites brevipalpis Theobald. The HI, CI and BI for Ae. aegypti were high in all the study locations, but low for Ae. lueteocephalus except in Ega. With 50 immature Aedes mosquitoes screened across locations, only Ae. aegypti from Ega were positive for YF. This study places Ega on a high alert of an impending YF outbreak. Thus, urgent steps to clear this area of potential mosquito sites are highly recommended.

Assessment of productivity of Culex spp. larvae (Diptera: Culicidae) in urban storm water catch basin system in Wroclaw (SW Poland).

In urban environments, catch basins serve as major developmental and resting sites for anthropophilic and zoophilic mosquitoes. However, the use of this habitat is inconsistent, with abundance of larvae varying significantly across catch basins at a fine spatial scale. During seasonal summer investigations on mosquito species composition, their spatial and temporal distribution and the environmental characteristic of the breeding sites in the underground storm drain systems of the Wroclaw urban area (SW Poland) were assessed from May to September in 2012-2013. The study was conducted in order to develop a rational strategy to control mosquito populations and prevent the potential human exposure to mosquito-transmitted pathogens. Mosquito larvae and pupae were collected and identified weekly from 100 regularly inspected street catch basins located in the town center. All existing and potential breeding habitats in the study area were recorded using a GPS receiver (Magellan MobileMapper CX) and transferred to the computer database. Collected data on the geographical location of inspected breeding places, water quality parameters in inspected catch basins, daily temperature, and precipitation were imposed on orthophotomap in ArcGIS (ESRI, USA). Water quality parameters including pH, electrical conductivity, and water temperature were measured by standard methods. Chemical water analysis of cations (Na(+), NH4 (+), K(+), Mg(2+), Ca(2+)) and anions (Cl(-), NO2 (-), NO3 (-), SO4 (2-)) were carried out using Waters Alliance high-performance liquid chromatograph (HPLC) 2695 with 432 Conductivity Detector and 2998 Photodiode Array Detector, an IC-Pak Anion HR column (glauconate/borate eluent) and IC-Pak Cation M/D column (EDTA/HNO3 eluent). Over two seasonal studies and 3739 samplings in total, 3669 mosquito larvae and 274 pupae/1 dip (from 0 to 110 individuals/dip) were collected by dipper. Culex pipiens s.l. (L.) and Cx. torrentium (Martini) prevailed at all catch basins of the study area as the predominant species. In all examined catch basins, autogenous individuals dominated by far. Breeding activity was first detected in early May. Peak abundance of Culex spp. population in many catch basins was observed in June 2012 and August 2013 when average daily temperatures were increasing and rainfall had declined. Dry periods between rainfalls varied during 2 years of the study period and were noted on June 2012 as well as on July and August 2013. Organically enriched catch basins with significant higher concentrations of Na(+) and NO3 (-) were found to be more productive breeding habitats. Differences in the Culex immature stage density based on the variables of habitat type, temperature, and precipitation support the need for ongoing surveillance in communities to guide public health officials in planning for and prioritizing mosquito control efforts.

New baseline environmental assessment of mosquito ecology in northern Haiti during increased urbanization.

The catastrophic 2010 earthquake in Port-au-Prince, Haiti, led to the large-scale displacement of over 2.3 million people, resulting in rapid and unplanned urbanization in northern Haiti. This study evaluated the impact of this unplanned urbanization on mosquito ecology and vector-borne diseases by assessing land use and change patterns. Land-use classification and change detection were carried out on remotely sensed images of the area for 2010 and 2013. Change detection identified areas that went from agricultural, forest, or bare-land pre-earthquake to newly developed and urbanized areas post-earthquake. Areas to be sampled for mosquito larvae were subsequently identified. Mosquito collections comprised five genera and ten species, with the most abundant species being Culex quinquefasciatus 35% (304/876), Aedes albopictus 27% (238/876), and Aedes aegypti 20% (174/876). All three species were more prevalent in urbanized and newly urbanized areas. Anopheles albimanus, the predominate malaria vector, accounted for less than 1% (8/876) of the collection. A set of spectral indices derived from the recently launched Landsat 8 satellite was used as covariates in a species distribution model. The indices were used to produce probability surfaces maps depicting the likelihood of presence of the three most abundant species within 30 m pixels. Our findings suggest that the rapid urbanization following the 2010 earthquake has increased the amount of area with suitable habitats for urban mosquitoes, likely influencing mosquito ecology and posing a major risk of introducing and establishing emerging vector-borne diseases.

Morphological and molecular characterization of the ecological, biological and behavioural variants of the JE vector Culex tritaeniorhynchus: an assessment of its taxonomic status.

BACKGROUND & OBJECTIVES: Culex tritaeniorhynchus (Diptera: Culicidae), an important vector of Japanese encephalitis belongs to the Culex vishnui subgroup which includes two other vector species namely, Cx. Vishnui and Cx. pseudovishnui. Many varieties and types of Cx. tritaeniorhynchus have been reported, besides populations that exhibit behavioural and biological differences. This study was undertaken to find out whether Cx. tritaeniorhynchus populations exhibiting behavioural and biological variations, and those from different geographical areas, are comprised of more than one taxon or belong to a single taxon. METHODS: Morphological characterization was done by examining 153 morphological and morphometric characters in the larval (75), pupal (60) and adult stages (18) of five geographical populations of Cx. tritaeniorhynchus. Molecular characterization was done by PCR amplification of mitochondrial cytochrome c oxidase (COI) gene sequences (DNA barcodes) and another hypervariable genetic marker, the ribosomal DNA (16S). One-way ANOVA, principal component analysis (PCA) and discriminant factor analysis (DFA) were done for statistical analyses using the statistical package SPSS IBM version 19.0. RESULTS: Morphological characterization showed that no intraspecific differentiation can be made among the five geographical populations of Cx. tritaeniorhynchus. Molecular characterization done by DNA barcoding also showed that the COI sequences of all the five populations of Cx. tritaeniorhynchus grouped into a single taxonomic clade plus the genetic differentiation among these was non-significant and the overall gene flow among the populations was very high. Analysis of the ribosomal DNA also confirmed that the Cx. tritaeniorhynchus populations belonged to a single taxon. INTERPRETATION & CONCLUSION: Culex tritaeniorhynchus is a taxon that does not involve cryptic species.

ASSESSMENT OF PUPAL PRODUCTIVITY OF AEDES AND CO-OCCURRING MOSQUITOES IN KOLKATA, INDIA.

Monitoring of dengue vectors provide baseline information about the abundance and subsequent management strategy. An appraisal of mosquito abundance using dengue vectors as focal species was made in respect to Kolkata, India as geographical area. The data on immature abundance in the container larval habitats viz, earthen, porcelain and plastic materials were subjected to three-way factorial ANOVA, using months, habitats and species as variables. Similar tests were done on pupal weight and wing length. It was observed that Anopheles subpictus, Culex quinquefasciatus coexist with Ae. aegypti and Ae. albopictus in different container habitats, that varied with months and habitats. Ae. aegypti and Ae. albopictus were found in higher proportions in porcelain and plastic containers. In earthen containers a stable ratio of three mosquitoes was observed. Sex specific variations in pupal weight and wing length were noted in both species of Ae. aegypti and Ae. albopictus. The wing length of adult Aedes mosquitoes showed correspondence with pupal weight suggesting the use of pupal weight can be used as indicator of prospective adult body size. Although less known as container breeding, presence of An. subpictus and Cx. quinquefascistus along with Aedes indicates that availability of waste containers in environment increases risks of dengue and other mosquito borne diseases. The present habitat-based study calls for a strict vector management strategy to reduce the sources of ovipostion in various container habitats to minimize the mosquito vectors and thus potential risk of dengue and other mosquito borne diseases.

A novel cost-effective medium for the production of Bacillus thuringiensis subsp. israelensis for mosquito control.

Bacillus thuringiensis subsp. israelensis (Bti) has been used for mosquito-control programmes the world-wide. Indeed, the large-scale production of Bti for mosquito control is very expensive due to the high cost of its culture. In the present study, we attempted to widen the scope in developing cost-effective culture medium for Bti production, based on the raw materials available on the biosphere, including coconut cake powder, CCP (Cocos nucifera), neem cake powder, NCP (Azadirachta indica) and groundnut cake powder, GCP (Arachis hypogea). Among these raw materials, the biomass production of Bti, sporulation and toxin synthesizing from 'CCP' in combination with mineral salt (MnCl(2)) was comfortably satisfactory. Bioassays with mosquito species (Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti) and field trials were also satisfactory. The present investigation suggests that coconut cake-based culture medium can be used as an alternative for industrial production of Bti in mosquito-control programme. Therefore, the study is very important from the point of effective production of Bti from cost-effective culture medium for the control of mosquito vectors.

The costs of infection and resistance as determinants of West Nile virus susceptibility in Culex mosquitoes.

BACKGROUND: Understanding the phenotypic consequences of interactions between arthropod-borne viruses (arboviruses) and their mosquito hosts has direct implications for predicting the evolution of these relationships and the potential for changes in epidemiological patterns. Although arboviruses are generally not highly pathogenic to mosquitoes, pathology has at times been noted. Here, in order to evaluate the potential costs of West Nile virus (WNV) infection and resistance in a primary WNV vector, and to assess the extent to which virus-vector relationships are species-specific, we performed fitness studies with and without WNV exposure using a highly susceptible Culex pipiens mosquito colony. Specifically, we measured and compared survival, fecundity, and feeding rates in bloodfed mosquitoes that were (i) infected following WNV exposure (susceptible), (ii) uninfected following WNV exposure (resistant), or (iii) unexposed. RESULTS: In contrast to our previous findings with a relatively resistant Cx. tarsalis colony, WNV infection did not alter fecundity or blood-feeding behaviour of Cx. pipiens, yet results do indicate that resistance to infection is associated with a fitness cost in terms of mosquito survival. CONCLUSIONS: The identification of species-specific differences provides an evolutionary explanation for variability in vector susceptibility to arboviruses and suggests that understanding the costs of infection and resistance are important factors in determining the potential competence of vector populations for arboviruses.

The effect of spatial and temporal subsetting on Culex tarsalis abundance models--a design for sensible reduction of vector surveillance.

Early identification of increasing mosquito activity is critical to effective mosquito control, particularly when increasing host-seeking behavior may be associated with increased risk of mosquito-borne disease. In this paper, we analyzed the temporal abundance pattern of the West Nile Virus vector, Culex tarsalis, in Fort Collins, CO, using an autoregressive integrated moving average model. We determined that an autoregressive model order 5 with lagged minimum temperatures was best at describing the seasonal abundance of Cx. tarsalis. We then tested the effect of using both temporal and spatial subsets of the data to determine the effect of reduced sampling effort on abundance predictions. We found that, if reduced trapping is necessary due to limited resources, removal of the least productive 1/3 or 1/4 of the traps produced the least erroneous predictions of seasonality represented in the observed data. We show that this productivity-based subset scheme performs better than other sampling effort reductions in generating the best estimate of Cx. tarsalis abundance per trap-night.

A mosquito predator survey in Townsville, Australia, and an assessment of Diplonychus sp. and Anisops sp. predatorial capacity against Culex annulirostris mosquito immatures.

A twelve-month survey for mosquito predators was conducted in Townsville, Queensland, Australia, which is located in the arid tropics. The survey revealed the presence of five predaceous insects but only Anisops sp. (backswimmers) and Diplonychus sp. were common. Predatorial capacity and factors influencing this capacity were then assessed for adult Anisops sp. and adult and nymph stages of Diplonychus sp. against Culex annulirostris mosquito immatures under laboratory conditions. Predatorial capacity bioassays showed that adult Diplonychus sp. preyed upon both larval and pupal stages of Cx. annulirostris quite successfully. Nymphs of Diplonychus sp. proved to be more successful with smaller prey immatures, and Anisops sp adults did not prey successfully on any prey pupae. Increasing the foraging area and introducing aquatic vegetation significantly reduced the predatorial capacity of Diplonychus sp. nymphs, while only vegetation and not foraging area had a significant effect on adult Diplonychus sp. predation capacity. Overall, adult Diplonychus sp. proved to be a more efficient predator than Anisops sp., and field trials are now recommended to further assess the potential of Diplonychus sp. as a biocontrol agent.

High Wolbachia density correlates with cost of infection for insecticide resistant Culex pipiens mosquitoes.

In the mosquito Culex pipiens, insecticide resistance genes alter many life-history traits and incur a fitness cost. Resistance to organophosphate insecticides involves two loci, with each locus coding for a different mechanism of resistance (degradation vs. insensitivity to insecticides). The density of intracellular Wolbachia bacteria has been found to be higher in resistant mosquitoes, regardless of the mechanism involved. To discriminate between costs of resistance due to resistance genes from those associated with elevated Wolbachia densities, we compared strains of mosquito sharing the same genetic background but differing in their resistance alleles and Wolbachia infection status. Life-history traits measured included strength of insecticide resistance, larval mortality, adult female size, fecundity, predation avoidance, mating competition, and strength of cytoplasmic incompatibility (CI). We found that: (1) when Wolbachia are removed, insecticide resistance genes still affect some life-history traits; (2) Wolbachia are capable of modifying the cost of resistance; (3) the cost of Wolbachia infections increases with their density; (4) different interactions occurred depending on the resistance alleles involved; and (5) high densities of Wolbachia do not increase the strength of CI or maternal transmission efficiency relative to low Wolbachia densities. Insecticide resistance genes generated variation in the costs of Wolbachia infections and provided an interesting opportunity to study how these costs evolve, a process generally operating when Wolbachia colonizes a new host.

West Nile virus risk assessment and the bridge vector paradigm.

In the northeast United States, control of West Nile virus (WNV) vectors has been unfocused because of a lack of accurate knowledge about the roles different mosquitoes play in WNV transmission. We analyzed the risk posed by 10 species of mosquitoes for transmitting WNV to humans by using a novel risk-assessment measure that combines information on the abundance, infection prevalence, vector competence, and biting behavior of vectors. This analysis suggests that 2 species (Culex pipiens L. and Cx. restuans Theobald [Diptera: Cilicidae]) not previously considered important in transmitting WNV to humans may be responsible for up to 80% of human WNV infections in this region. This finding suggests that control efforts should be focused on these species which may reduce effects on nontarget wetland organisms. Our risk measure has broad applicability to other regions and diseases and can be adapted for use as a predictive tool of future human WNV infections.

Insecticide resistance genes confer a predation cost on mosquitoes, Culex pipiens.

Newly occurring adaptive genes, such as those providing insecticide resistance, display a fitness cost which is poorly understood. In order to detect subtle behavioural changes induced by the presence of resistance genes, we used natural predators and compared their differential predation on susceptible and resistant Culex pipiens mosquitoes, using strains with a similar genetic background. Resistance genes were either coding an overproduced detoxifying esterase (locus Ester), or an insensitive target (locus ace-1). Differential predation was measured between susceptible and resistant individuals, as well as among resistant mosquitoes. A backswimmer, a water measurer, a water boatman and a predaceous diving beetle were used as larval predators, and a pholcid spider as adult predator. Overall, the presence of a resistance gene increased the probability of predation: all resistance genes displayed predation costs relative to susceptible ones, at either the larval or adult stage, or both. Interestingly, predation preferences among the susceptible and the resistance genes were not ranked uniformly. Possible explanations for these results are given, and we suggest that predators, which are designed by natural selection to detect specific behavioural phenotypes, are useful tools to explore non-obvious differences between two classes of individuals, for example when they differ by the presence or absence of one recent gene, such as insecticide resistance genes.

Study of larvivorous fish for malaria vector control in Somalia, 2002.

An intervention study was conducted on the introduction of the larvivorous fish Oreochromis spilurus spilurus as a method of malaria vector control in Kalabeydh village, northern Somalia. This species is resistant to chlorine in water up to a concentration of 1.0 mg/L. Fish were introduced into 25 berkit (reservoirs). After 1 month the number of larvae in each berkit was reduced by between 16.5% and 78.6% (mean 52.8%). Community acceptance and participation was good. The introduction of larvivorous fish is a cheap method of malaria vector control, but its sustainability needs special consideration and education of the community is important, especially to cover the dry season, when most of the berkit dry up.

Spatial analysis of West Nile virus: rapid risk assessment of an introduced vector-borne zoonosis.

The distribution of human risk for West Nile virus was determined by spatial analysis of the initial case distribution for the New York City area in 1999 using remote sensing and geographic information system technologies. Cluster analysis revealed the presence of a statistically significant grouping of cases, which also indicates the area of probable virus introduction. Within the cluster, habitat suitability for potentially infective adult mosquitoes was measured by the amount of vegetation cover using satellite imagery. Logistic regression analysis revealed satellite-derived vegetation abundance to be significantly and positively associated with the presence of human cases. The logistic model was used to estimate the spatial distribution of human risk for West Nile virus throughout New York City. Accuracy of the resulting risk map was cross-validated using virus-positive mosquito sample sites. These new epidemiological methods aid in rapid entry point identification and spatial prediction of human risk of infection for introduced vector-borne pathogens.