Understanding spatial patterns of human risk of exposure to arthropod vectors and their associated pathogens is critical for targeting limited prevention, surveillance, and control resources (e.g., spatial targeting of vaccination, drug administration, or education campaigns; use of sentinel sites to monitor vector abundance; and identifying areas for most effective use of pesticides). Vector-borne disease risk can, in many cases, be modeled with high predictive accuracy by using geographic information system approaches because abundances of vectors and pathogen reservoirs often are associated with environmental factors. Spatial risk models for human exposure to vector-borne pathogens, which ideally should have high accuracy for predicting areas of elevated risk without overestimating risk coverage, can be constructed based on epidemiological data or abundance of vectors or infected vectors. We use five bacterial or viral vector-borne diseases occurring in the United States and with pathogen transmission by fleas (plague), ticks (Lyme disease and tularemia), or mosquitoes (dengue and West Nile virus disease) to 1) examine how spatial risk of human exposure to vector-borne pathogens typically is presented to the public health community and public and 2) evaluate the utility of basing spatial risk models on epidemiological data relative to data for arthropod vectors or infected vectors. Recommended future directions for vector-borne disease risk modeling include development of subcounty level spatial risk models combining epidemiological and vector data and the use of simulation or analytical models to assess critical vector abundance thresholds required for enzootic pathogen maintenance.

Two species of Chirorhynchobiidae, Chirorhynchobia glossophaga sp. n. and Chirorhynchobia matsoni Yunker, 1970 are described and redescribed, respectively. The male of C. glossophaga and the tritonymph of C. matsoni are the first to be described in the family. The mites are ectoparasites living on the wing membrane of phyllostomid bats Glossophaga soricina (Pallas) from Peru and Anoura geoffroyi Gray from several localities. Females of the new species differ from those of C. matsoni by the shorter idiosoma (length 439–450 versus 497–562 in C. matsoni), by the dorsal position of setae 4a (terminal in C. matsoni), and by the narrower posterior projections of the propodonotal shield (width 6 versus 17). Although the morphology of Chirorhynchobiidae is strongly regressive, homologies of the leg and idiosomal setae in these mites with those of other Astigmata are established. The combination of absence of famulus [Private character epsilon] and solenidia σI-II and presence of solenidia ω1I-II and ω3I in these mites is shared with the Rhyncoptidae–Sarcoptidae clade, suggesting a possible relationship with those groups.

The identification of the members of the Culex pipiens L. complex in arbovirus surveillance programs relies heavily on the use of morphology. In this work, we studied Cx. pipiens complex male mosquitoes collected from nine different locations, from northern, southern, and the hybrid zone sites in North America; Cairo, Egypt; and Nairobi, Kenya. Specimens were identified using DV/D ratio and also using amplification of the acetylcholinesterase (ACE.2) gene by both conventional and real-time polymerase chain reaction, and examination of the CQ11 locus. Consistent with previous findings, the morphological and molecular identifications did not always agree, particularly in regions of extensive introgression. There was an increased frequency of hybrid forms in late summer and early fall in Champaign Co., IL, that is north of the previously described Cx. pipiens complex hybrid zone. This represents an expansion of the North American hybrid zone. The biological and epidemiological relevance of the high degree of introgression and the late season increase in the proportion of intermediate forms is discussed.

Climate differences across latitude can result in seasonal constraints and selection on life history characters. Since Aedes albopictus (Skuse) invaded North America in the mid-1980s, it has spread across a range of ≈14° latitude and populations in the north experience complete adult mortality due to cold winter temperatures that are absent in the south. Life table experiments were conducted to test for differences in the adult survival and reproductive schedules of Ae. albopictus females from two populations from the northern (Bloomington, IN [BL] and Manassas, VA [VA]; ≈39° N) and southern (Tampa, FL and Fort Myers, FL; ≈27–28° N) extremes of the species distribution in North America. Regardless of population origin, age-specific hazard rate increased with reproductive output and decreased with number of bloodmeals. Larger females took fewer bloodmeals, and they had greater hazard rates than did smaller females. There were no consistent differences between northern versus southern populations in resource allocation between reproduction and maintenance, reproduction over time, and reproductive investment among offspring, suggesting that latitudinal variation in climate is probably not a main selective factor impinging on adult mortality and reproductive schedules. One possible effect of climate on geographic differences in life history was detected. BL had lower survivorship, lower lifetime reproductive output, and lower adult reproductive rate than did all other populations. This result may be an indirect result of lower egg survivorship due to the severity of winter in BL compared with other populations, including VA at approximately the same latitude. Such a scenario may make the BL population more prone to extinction, irregularly recolonized from more favorable sites, and thus more susceptible to founder effects, genetic drift, and inbreeding, resulting in lower mean values of fitness-related traits.

Ongoing work in oak woods in Killarney National Park in southwestern Ireland is focusing on the factors influencing the fine-scale aggregated distribution of Ixodes ricinus L. (Acari: Ixodidae) on the ground. The extent of reuse of stems of vegetation as questing points by adult ticks was determined by paint-marking stems on which ticks were found, counting and removing these ticks, and subsequently reexamining the same stems for ticks on two further occasions. Overall, an estimated 2,967 stems in 123 separate rush plants (Juncus effusus L.) were examined. Statistical analysis of the data demonstrated a highly significant reoccupancy by ticks of stems previously and recently used. Furthermore, it is shown that the extent of stem reuse by ticks is significantly and positively correlated with the numbers of ticks originally observed on those stems. Although other factors may be involved in generating clumping of ticks, the results are compatible with the proposition that aggregation of I. ricinus on the ground is pheromone-mediated. The findings are discussed in relation to what is known about the powers of lateral movement of I. ricinus on the ground and the possible implications for the performance of tick traps.

Understanding genetic variation among populations of medically significant pest insects is important in studying insecticide resistance and insect dispersal. The bed bug, Cimex lectularius L. (Hemiptera: Cimicidae), is widespread hematophagus insect pest around the world, including North America, and it has recently been identified as an emerging resurgent pest. To date, no studies have been conducted on genetic variation of this species. For this study, 136 adult bed bugs representing 22 sampled populations from nine U.S. states, Canada, and Australia were subjected to genetic analysis using polymerase chain reaction (PCR) to amplify and sequence a region of the mitochondrial DNA (mtDNA) 16S rRNA gene and a portion of the nuclear rRNA internal transcribed spacer (ITS) 1 region. For the 397-bp 16S marker, a 12 nucleotide sites in total were polymorphic, and 19 unique haplotypes were observed. Heterozygosity was observed within many of the sampled populations for the mtDNA marker. This suggests that bed bug populations did not undergo a genetic bottleneck as one would expect from insecticide control during the 1940s and 1950s, but instead, that populations may have been maintained on other hosts such as birds and bats. In contrast to the high amount of heterozygosity observed with the mitochondrial DNA marker, no genetic variation in the 589-bp nuclear rRNA marker was observed. This suggests increased gene flow of previously isolated bed bug populations in the United States, and given the absence of barriers to gene flow, the spread of insecticide resistance may be rapid.

In the major malaria vector Anopheles gambiae Giles, two point mutations at the voltage-gated sodium channel have been associated with knockdown resistance (kdr) to DDT and pyrethroid insecticides. Simple allele-specific polymerase chain reaction (PCR) assays to detect these single-nucleotide polymorphisms are prone to lack of specificity and therefore alternative techniques have been proposed. However, these may not be easily implemented in many laboratories from malaria endemic regions. Here, we describe a primer-introduced restriction analysis (PIRA)-PCR method to detect kdr mutations in An. gambiae. This method unambiguously identified all six genotypes for the kdr locus in a sample of 113 field-collected mosquitoes for which kdr genotypes had been confirmed by DNA sequencing. Co-occurrence of both kdr alleles was found in sites from Equatorial Guinea and Gabon and the L1014F mutation was detected in M-form individuals from Angola. The PIRA-PCR proved to be a reliable, robust, and simpler alternative for the detection of kdr mutations in this malaria vector.

Pyrethroid-treated bed-nets and indoor spray are important components of malaria control strategies in Kenya. Information on resistance to pyrethroid insecticides in Anopheles gambiae and An. arabiensis populations is essential to the selection of appropriate insecticides and the management of insecticide resistance. Monooxygenase activity and knockdown resistance (kdr) allele frequency are biochemical and molecular indicators of mosquito resistance to pyrethroids. This study determined baseline information on monooxygenase activity and kdr allele frequency in anopheline mosquitoes in the western region, the Great Rift Valley–central region, and the coastal region of Kenya. In total, 1,990 field-collected individuals, representing 12 An. gambiae and 22 An. arabiensis populations were analyzed. We found significant among-population variation in monooxygenase activity in An. gambiae and An. arabiensis and substantial variability among individuals within populations. Nine of 12 An. gambiae populations exhibited significantly higher average monooxygenase activity than the susceptible Kisumu reference strain. The kdr alleles (L1014S) were detected in three An. gambiae populations, and one An. arabiensis population in western Kenya, but not in the Rift Valley–central region and the coastal Kenya region. All genotypes with the kdr alleles were heterozygous, and the conservative estimation of kdr allele frequency was below 1% in these four populations. Information on monooxygenase activity and kdr allele frequency reported in this study provided baseline data for monitoring insecticide resistance changes in Kenya during the era when large-scale insecticide-treated bed-net and indoor residual spray campaigns were being implemented.

The behavioral and physiological responses of 6-d-old Aedes aegypti (L.) adult females exposed to deltamethrin and DDT were characterized using a free-choice excito-repellency test system. Excluding varying pretest age and carbohydrate availability as possible confounders, insecticide contact (measuring irritancy) and noncontact (measuring repellency) behavioral assays were conducted on two nonbloodfed groups, either unmated or mated (nulliparous), and two blood-fed groups, either parous or newly full-engorged mosquitoes. The degree of escape response to deltamethrin and DDT varied according to the physiological conditioning. Escape rates from contact and noncontact chambers with deltamethrin were more conspicuous in nonbloodfed groups compared with mosquitoes previously bloodfed. There were no significant differences in escape responses between unmated and nulliparous test populations. With DDT, a more pronounced escape response was observed in unmated compared with other physiological conditions. More moderate escape response was seen in nulliparous mosquitoes, and the least was observed in full bloodfed test individuals, regardless of test compound. Ae. aegypti, regardless of pretest conditioning, was completely susceptible to deltamethrin, whereas showing high resistance to DDT. Despite profound differences in resistance, there was no significant difference in avoidance response between chemicals and mosquito conditioning. Moreover, pre- and postbloodmeals were found to influence assay outcome and thus to have relevance on the interpretation of susceptibility and excito-repellency assays.

The spread of insecticide resistance genes in Anopheles gambiae Giles sensu stricto threatens to compromise vector-based malaria control programs. Two mutations at the same locus in the voltage-gated sodium channel gene are known to confer knockdown resistance (kdr) to pyrethroids and DDT. Kdr-e involves a leucine-serine substitution, and it was until recently thought to be restricted to East Africa, whereas kdr-w, which involves a leucine-phenylalanine substitution, is associated with resistance in West Africa. In this study, we analyze the frequency and relationship between the kdr genotypes and resistance to type I and type II pyrethroids and DDT by using WHO test kits in both the Forest-M and S molecular forms of An. gambiae in Cameroon. Both kdr-w and kdr-e polymorphisms were found in sympatric An. gambiae, and in many cases in the same mosquito. Kdr-e and kdr-w were detected in both forms, but they were predominant in the S form. Both kdr-e and kdr-w were closely associated with resistance to DDT and weakly associated with resistance to type II pyrethroids. Kdr-w conferred greater resistance to permethrin than kdr-e. We also describe a modified diagnostic designed to detect both resistant alleles simultaneously.

Several species of the spotted fever group Rickettsia (SFGR), with considerable variation in vertebrate host pathogenicity, are present in ticks in the United States. In this study, quantitative real-time PCR (qPCR) was used to characterize the growth and the distribution of Rickettsia amblyommii in selected tissues (salivary glands, gut, and ovaries) of naturally infected Amblyomma americanum (L.) (Acari: Ixodidae), during bloodmeal acquisition and throughout vertical transmission to eggs and postembryonic life cycle stages (larvae and nymphs). R. amblyommii was identified in the samples at ratios of ≤1 rickettsiae per tick cell. Significant variability in the ratio of rickettsial to tick gene copy numbers between the tissues was identified; however, no single tissue was consistently observed to have the greatest rickettsial burden throughout the feeding event. Furthermore, the ratio of rickettsial to tick gene copy numbers did not significantly differ between eggs, immature ticks, and feeding events. This is the first study to use qPCR to enumerate rickettsial growth and distribution in the tick host during bloodmeal acquisition. Deciphering SFGR tissue distribution and transmission mechanisms is necessary for the development of novel approaches to control tick-borne rickettsial diseases.

Host-seeking heights, host-seeking activity patterns, and West Nile virus (family Flaviviridae, genus Flavivirus, WNV) infection rates were assessed for members of the Culex pipiens complex from July to December 2002, by using chicken-baited can traps (CT) at four ecologically different sites in Shelby County, TN. Host-seeking height was assessed by CT placed at elevations of 3.1, 4.6, and 7.6 m during one 24-h period per month. Host-seeking activity was assessed by paired CT placed at an elevation of 4.6 m. Can traps were sampled at one 10-h daytime interval and at seven 2-h intervals during the evening, night, and morning. Cx. pipiens complex mosquitoes accounted for 87.1% of collected mosquitoes. Culex (Melanoconion) erraticus (Dyar & Knab) accounted for 11.9% of specimens. The average number of Cx. pipiens complex mosquitoes collected per 24-h CT period from July to September was lowest at a rural middle income site (1.7), intermediate at an urban middle income site (11.3), and highest at an urban low income site (47.4). Can traps at the forested site failed to collect Cx. pipiens complex mosquitoes. From July to September at urban sites, Culex pipiens pipiens L. was the rarest of the three complex members accounting for 11.1–25.6% of specimens. At the rural site, Culex pipiens quinquefasciatus Say was the rarest member of the complex. Cx. p. pipiens was not collected after September. Mean abundance of Cx. pipiens complex mosquitoes was higher in traps at 7.6 m than in traps at 4.6 m. Abundances at 3.1 m were intermediate and not significantly different from abundances at the other heights. Initiation of host-seeking activity was associated with the end of civil twilight and activity occurred over an extended nighttime period lasting 8–10 h. All 11 WNV-positive mosquitoes were Cx. pipiens complex mosquitoes collected from urban sites in traps placed at elevations of 4.6 and 7.6 m. Infection rates were marginally nonsignificant by height. Infection rates, host-seeking heights, and activity patterns were not significantly different among members of the Cx. pipiens complex.

In total, 394 questing adult blacklegged ticks, Ixodes scapularis Say (Acari: Ixodidae), collected at four sites were analyzed by polymerase chain reaction (PCR) for five microbial species: Anaplasma phagocytophilum, Babesia microti, Babesia odocoilei, Borrelia burgdorferi, and the rickettsial I. scapularis endosymbiont. Identities of genetic variants of A. phagocytophilum were determined by sequencing a portion of the 16S DNA. In 55% of infected ticks (193/351), a single agent was detected. In 45% (158/351), two or more agents were detected; 37% harbored two agents and 8% harbored three agents. One male tick, collected from Ft. McCoy, WI, harbored all four microbial genera. The highest rates of co-infection were by the Ixodes endosymbiont and B. burgdorferi (95/351). Two species of Babesia co-occurred within a single tick population in Wells National Estuarine Research Reserve, Wells, ME, whereas only B. odocoilei was found in other tick populations. Only A. phagocytophilum human anaplasmosis variant was detected in questing ticks from Tippecanoe River State Park, IN; from Wells; and Ft. McCoy, whereas a single infected tick from Presque Isle, PA, was infected by AP-Variant 1. Partially engorged ticks from deer in Tippecanoe River State Park were all infected with AP-Variant 1. Frequency of infections with each agent varied among populations. Rates and types of co-infections were not significantly different from random except for the Ixodes endosymbiont and B. burgdorferi in male ticks, which co-occurred less frequently than expected. Thus, I. scapularis hosts an array of pathogenic and symbiotic agents and potential evidence of interactions among microbial species was observed.

Recently, high resistance to pyrethroid insecticides has been associated with ineffective field treatments against Triatoma infestans (Klug) (Hemiptera: Reduviidae) in northern Argentina. Samples were collected from two areas in Argentina (Salta and La Rioja) and one are in Bolivia (Yacuiba), and they were subjected to toxicological and biochemical assays. All populations were resistant to deltamethrin, but they showed different profiles to nonpyrethroid insecticides. The Salta population showed high resistance ratios (RRs) to deltamethrin and only slight differences in the susceptibility to fenitrothion and fipronil compared with the reference strain. Otherwise, the La Rioja population showed a lower RR to deltamethrin and no resistance to fenitrothion or fipronil. Finally, the Yacuiba population had high a RR to deltamethrin, but it was susceptibility to fenitrothion and fipronil. In several cases, deltamethrin-resistant populations had higher susceptibility to bendiocarb than the reference strain. Measured activity of P450 monooxygenase in individual insects (based on ethoxycoumarine-O-deethylase), tended to be higher in the deltamethrin-resistant populations, but the differences were not statistically significant. Activity of specific esterases determined by the hydrolysis of 7-coumaryl permethrate demonstrated an increase in the percentage of insects with higher esterase activity in the Salta and La Rioja populations. Unexpectedly, the Yacuiba population showed lower pyrethroid esterase activity than the reference strain. The different pyrethroid resistance patterns found in T. infestans from three geographical regions within Argentina and in Bolivia suggests that enzyme-based pyrethroid resistance in this species has multiple origins. Nevertheless, because nerve insensitivity (related to the presence of the kdr gene) is also an important mechanism related to pyrethroid resistance, further studies on the kdr gene should be carried to clarify the relative contribution of each pyrethroid-associated mechanism in deltamethrin-resistant populations of T. infestans.

The assumption that mosquito survival remains constant and that it is independent of age was tested with free-ranging Aedes aegypti (L.) (Diptera: Culicidae) by using a “synthetic cohort” mark–release–recapture method. Mosquito age cohorts (1–2, 3–4, and 19–20 d) were released simultaneously in homes in rural Thai villages during dry and rainy seasons (2002). Significant age-dependent effects were detected during the dry and rainy seasons. More young than older mosquitoes were recaptured (1–4 versus 5–20 d). The best predictive fit for recaptures was obtained using a quadratic function of age. Our results provide the first field-based evidence for age-dependent Ae. aegypti mortality in which the death rate increases with advancing age and highlight the need for research on ecological and epidemiological aspects of this process.

The spatial heterogeneity of questing Ixodes ricinus (L.) (Acari: Ixodidae) within endemic areas in Great Britain is well established. Their presence is acutely responsive to blood host availability and their ability to maintain water balance, which are in turn governed by a variety of ecological and environmental factors. This article details the findings of a 3-yr study on the Gower peninsula, south Wales, which investigated the contribution of such factors (both ground- and geographic information systems [GIS]-derived) for predicting the presence of questing I. ricinus (Q_P), at a local scale. Statistically significant univariate associations were found between Q_P and calcareous/neutral grassland and heathland habitats, particularly those grazed by livestock, and various factors that intuitively promote tick survival. For example, topographical features, such as certain aspects, that reduce exposure to cold northerly winds and the hot midday sun, favored Q_P. Similarly, positive associations were found with substrata composed of less permeable soil types and less permeable superficial/bedrock geologies that promote a moist microhabitat and reduce the likelihood of desiccation. Q_P was also higher in areas of high soil moisture. This study highlighted a number of GIS-derived data sets that could be applied in the development of local and national predictive maps for I. ricinus in Great Britain. An understanding of the influence of these factors on questing I. ricinus can aid targeted tick control programs and help to educate the public, and those occupationally exposed, in understanding likely I. ricinus prolific areas within an I. ricinus endemic region.

We have characterized gene expression changes in the midgut tissue of Culex nigripalpus Theobold (Diptera: Culicidae) females, after they ingest a bloodmeal, by differential display of RNA isolated from pre- and postfeeding females. Seventy-two cDNA fragments exhibiting reproducible differences were observed. Of these, 22 showed an increase in gene expression and 50 showed a decrease in gene expression as a result of blood feeding. Eleven cDNA fragments exhibiting increased expression after a bloodmeal were cloned and sequenced. Seven of these were novel transcripts, and they did not match any sequences in GenBank. Three clones were similar to conserved proteins of unknown function from Aedes aegypti (L.) and Anopheles gambiae Giles. Here, we present the expression data on the first cDNA clones isolated from Cx. nigripalpus midgut tissue, including their molecular characterization, and we discuss their possible involvement in blood-feeding–associated processes and disease transmission.

Adult body size is a central life history character in mosquito fitness studies. I evaluated the predictive values of pupal cephalothorax length, cephalothorax width, and wet weight for adult size (wing length) of male and female Aedes aegypti (L.) (Diptera: Culicidae). Cephalothorax length was the most consistent and accurate predictor of adult size. Width of the cephalothorax and wet weight were more variable, and they significantly decreased shortly before adult emergence. I propose that cephalothorax length could be used as a proxy for adult size to test how physical and biological factors such as resource-limited environments and competition affect mosquito fitness with the advantage that the specimen does not need to be killed.