If global warming progresses, many consider that malaria in presently malaria-endemic areas will become more serious, with increasing development rates of the vector mosquito and malaria parasites. However, the correlation coefficients between the monthly malaria cases and the monthly mean of daily maximum temperature were negative, showing that the number of malaria cases in tropical areas of Africa decreases during the season when temperature was higher than normal. Moreover, an analysis of temperature and development rate using a thermodynamic model showed that the estimated intrinsic optimum temperatures for the development of the malaria parasites, Plasmodium falciparum and P. vivax, in the adult mosquito stage and that of the vector mosquito Anopheles gambiae s.s. were all ≈23–24°C. Here, the intrinsic optimum temperature is defined in the thermodynamic model as the temperature at which it is assumed that there are no or negligible adverse effects for development. Therefore, this study indicates that the development of malaria parasites in their mosquito hosts and the development of their vector mosquitoes are inhibited at temperatures higher than 23–24°C. If global warming progresses further, the present center of malarial endemicity in sub-Saharan Africa will move to an area with an optimum temperature for both the vector and the parasite, migrating to avoid the hot environment.

Anopheles (Nyssorhynchus) benarrochi s.l., Anopheles (Nyssorhynchus) oswaldoi s.l., and Anopheles (Nyssorhynchus) konderi s.l. collected in Acrelândia, state of Acre, Brazil, were identified based on morphological characters of the male genitalia, fourth-instar larvae, and pupae. Morphological variation was observed in the male genitalia of these species in comparison with specimens from other localities in Brazil. DNA sequence from the nuclear ribosomal second internal transcribed spacer of individuals identified as An. benarrochi s.l. by using male genitalia characteristics showed that the various morphological forms are conspecific but are distinct from An. benarrochi B from Colombia. Anopheles konderi s.l. and An. oswaldoi s.l. both misidentified as An. oswaldoi s.s. (Peryassú) throughout Brazil, may actually comprise at least two undescribed species. Diagnostic morphological characteristics of the male genitalia are provided to distinguish Anopheles benarrochi s.l., Anopheles oswaldoi s.l., and Anopheles konderi s.l. from morphologically similar species. Incrimination of An. oswaldoi s.s. in malaria transmission in Brazil needs further investigation because other undescribed species from Acre may have been confounded with this taxon.

The specific aims of this work were to examine the antennal sensilla of Lutzomyia longipalpis (Lutz & Neiva 1912) (Diptera: Psychodidae) adults and to characterize their typology and topography, with special attention to olfactory sensilla. The surfaces of the antennal segments of Lu. longipalpis males and females were studied by scanning electron microscopy (SEM). Lu. longipalpis used in the current study were obtained from a colony originating from Lapinha Cave, Minas Gerais state, Brazil. Microtrichiae and 11 subtypes of sensilla were observed and characterized according to the following categories: five subtypes of trichoid sensilla (short, medium, long blunt-tipped, long pointed-tipped, and apical), two coeloconic sensilla (grooved and praying hands), and campaniform, chaetic, basiconic, and squamiform sensilla. SEM analyses showed few differences between males and females in the typology, topography, and quantity of antennal sensilla described. The current study is the first to identify several categories of antennal sensilla of the genus Lutzomyia and their distribution patterns. The identification of these sensillar types may be important in planning future electrophysiological studies to develop alternative measures of control and monitoring of Lu. longipalpis.

Cimex hemipterus (Fabricius) is a hematophagous insect that can be an experimental host of Trypanosoma cruzi and may play a role as vector of Chagas’ disease. This work analyzed the structure of the salivary glands of C. hemipterus. The secretory portion of main salivary glands has a single oval lobe that is translucent and is formed from a simple columnar epithelium lined by muscle cells. The gland cells are high, with one or two spherical nuclei, nucleolus, and some condensed chromatin. The cell cytoplasm has a well-developed rough endoplasmic reticulum, electron lucent vesicles, lysosomes, and glycogen deposits. The apical plasma membrane has microvilli, zonula adherens, and desmosomes, whereas the basal plasma membrane has some infoldings associated with mitochondria. The duct of the main salivary glands has flattened cells. The secretory portion of the accessory salivary glands is a single vesicular lobe that is translucent and is formed from a single layer of cells that varies from flattened to cubical onto muscle cells. The cytoplasm contains a well-developed smooth endoplasmic reticulum, vacuoles of different sizes containing secretions, electron lucent, and abundant mitochondria. The baso-lateral plasma membrane of adjacent cells shows septate junctions. The duct is formed from a flattened epithelium like the duct of the principal salivary gland. The secretory cells of the main salivary glands are related to protein synthesis and transport of ions. However, the secretory cells of the accessory salivary glands are related mainly to transport of ions and water from the hemolymph to glandular lumen.

Experiments were conducted to determine whether changes in skin temperature of cattle held at ambient temperatures ranging from 10°C to 30°C influenced engorgement of female Dermacentor andersoni (Stiles). Average skin temperature of Angus cattle increased from 29°C to 34°C, whereas skin temperature of Holstein cattle increased from 32°C to 35°C over the range of ambient temperatures. Changes in skin and ambient temperature strongly influenced the proportion of ticks that successfully engorged, the time required for engorgement, and weight of engorged ticks, and they had a weaker influence on the proportion of dead ticks. The relationships between the tick engorgement parameters and ambient temperature differed between the experiments using either Angus or Holstein cattle. The differences between experiments were reduced when expressed in relation to skin temperature, suggesting that the thermal environment of the breeds is an important characteristic determining engorgement success. Results indicate that ticks respond to changes in the thermal environment of the host, and these changes may be important to engorging ticks exposed to fluctuating spring weather.

The association of environmental factors with fluctuations in the density of the malaria vector Anopheles minimus (Theobald, 1901) was analyzed in Longtang and Dongfanghong, two villages in southern Yunnan Province, Peoples Republic of China. The distance of trap locations to rice fields and the distance from trap locations to rivulets were negatively correlated to the density of An. minimus. The length of a rivulet within a 1-km buffer around a trap location was positively correlated to the density of An. minimus, whereas the rice field area within a 1-km buffer of a trap location was negatively correlated to An. minimus dominance, but the length of a rivulet within a 1-km buffer around a trap location and the distance of trap locations to rice fields were positively correlated to An. minimus dominance. Linear models relating the density and dominance of An. minimus at trap sites in relation to environmental parameters are described. These results could help in the design of malaria control strategies.

Clearing of native vegetation for agriculture since European settlement has left 1.047 million ha of southwestern Australia affected by a severe form of environmental degradation called dryland salinity, characterized by secondary soil salinization and waterlogging. This area may expand by a further 1.7–3.4 million ha if current trends continue. Detailed investigations of seasonal of adult and larval mosquito population dynamics were undertaken in the region to test the hypothesis that the development of dryland salinity and waterlogging in inland southwestern Australia has led to a succession of mosquito species and increased Ross River virus (family Togaviridae, genus Alphavirus, RRV) transmission risk. Aedes (Ochlerotatus) camptorhynchus (Thomson) made up >90% of adult mosquito collections in saline regions. Nonmetric multidimensional scaling and generalized estimating equations modeling demonstrated that it was strongly associated with increasing severity of dryland salinity. This article describes the first detailed investigation of the mosquito fauna of inland southwestern Australia, and it is the first description of the influence of secondary soil salinity on mosquito population dynamics. Despite the dominant presence of Ae. camptorhynchus, RRV disease incidence is not currently a significant population health priority in areas affected by dryland salinity. Potential limiting factors include local climatic impacts on the seasonal mosquito population dynamics, vertebrate host distribution and feeding behavior of Ae. camptorhynchus, and the scarce and uneven distribution of the human population in the region.

Anthropogenic environmental disturbance is a significant factor driving mosquito community composition. However, researchers subjectively define environmental change creating difficulties for cross-study comparison. To examine the relationship between terrestrial change and mosquito composition, we used remote sensing techniques to define spatially explicit land use categories along a gradient with low (rural), medium (peri-urban), and high (urban) anthropogenic influence in the Peruvian Amazon. We found significant differences in mosquito diversity among land use categories. Our results provide baseline data linking mosquito distribution to land use in the Peruvian Amazon and present an easily replicable method of comparison for future research. Creating standardized methods to measure the impact of human influence on the environment is of particular importance in designing targeted public health policies and in predicting disease risk in rapidly changing environments such as the Amazon.

Culex territans Walker (Diptera: Culicidae) larvae share nonpolluted freshwater habitats with amphibians, which are bloodmeal hosts of their adults. To examine synchrony of Cx. territans with amphibian species, 10 larval habitat sites were sampled weekly from March to November of 2004. Cx. territans larvae were temporally and spatially associated with the green frog, Rana clamitans Latrielle. We predicted that if the preferred hosts were abundant at low temperatures, Cx. territans might be able to digest bloodmeals at those same temperatures. Using the thermal heat summation model, 192.3 d above 3.9°C were needed to complete the gonotrophic cycle. This is the lowest thermal minimum reported for a Nearctic species of mosquito. Using this model, we calculated that the first larvae of Cx. territans field collected on 6 May 2004 were the progeny of females that bloodfed during the last week of March or first week of April. We conclude that Cx. territans has physiological mechanisms that allow them to take advantage of early season bloodmeal sources.

In this study, a dual-choice oviposition bioassay was used to screen responses of gravid An. gambiae toward 17 bacterial species, previously isolated from Anopheles gambiae s.l. (Diptera: Culicidae) midguts or oviposition sites. The 10 isolates from oviposition sites have been identified by phylogenetic analyses of their 16S rRNA genes. Eight of the 10 isolates were gram-positive, out of which six belonged to the Bacilli class. Solid phase microextraction and gas chromatography coupled to mass spectrometry (GC-MS) were used to identify the volatiles emitted from the bacterial isolates. Aromatic and aliphatic alcohols, aliphatic ketones, alkylpyrazines, dimethyl oligosulfides, and indole were among the chemical compounds identified from the headspace above bacteria-containing saline. The mosquitoes laid significantly more eggs in six of the bacteria-containing solutions compared with the sterile solution. These six bacteria did not emit any compounds in common that could explain the positive oviposition response. Instead, the bacteria were grouped according to principal component analysis (PCA) based on the relative amounts of volatiles emitted. The PCA-plots facilitated the identification of 13 putative oviposition attractants for An. gambiae mosquitoes.

It has been suggested that mosquito larvae and pupae dive to avoid predators. We tested this predator-avoidance hypothesis by using immature Anopheles gambiae Giles (Diptera: Culicidae) and the wolf spider Pardosa messingerae (Stand) (Araneae: Lycosidae). Because previous studies have suggested that wolf spiders are poor predators of immature mosquitoes, we first examined the predatory ability of the wolf spider and found that the spider was effective at capturing all stages of larvae and pupae. The mortality from experimental cups containing deep water increased with the age of mosquitoes, with the exception of pupae. In contrast, this trend was not observed in shallow water. In particular, mortality was significantly lower in deep water during the second instar. During the third instar, the opposite trend was observed. When the effect of cannibalism was excluded by subtracting the number of missing mosquitoes for the treatment without spiders from those with spiders, the cannibalism corrected mortality was significantly lower in deep water during the second instar. The duration of diving by larvae and pupae decreased with age. With the exception of first instar, diving frequency also decreased with age. We postulate that this diving behavior allows An. gambiae to escape predation by wolf spiders, which supports the predator-avoidance hypothesis. This study indicates some important implications for vector control.

In the malaria vector Anopheles gambiae Giles sensu stricto, two molecular forms denoted M and S are considered units of incipient speciation within this species. Very low hybrid frequencies and significant genetic differentiation have been found in sympatric M- and S-form populations. We studied the molecular form composition and the degree of genetic differentiation at 15 microsatellites in two samples of An. gambiae collected in two consecutive years from Bissau, Guinea Bissau. High frequencies of M/S hybrids (19–24%) were found in this area. Coincidently, very low levels of genetic differentiation were detected between forms when analysis involved microsatellites mapped at chromosome-3 (mean F_st, 0.000–0.002). The single exception was the X-linked AGXH678, for which high differentiation was measured (F_st, 0.158–0.301). This locus maps near the centromere of chromosome X, a low recombination region in which selection is likely to promote divergence between M and S forms. These results strongly suggest that the degree of isolation between M and S forms, considered the units of incipient speciation within An. gambiae, is not homogenous throughout the species distribution range.

Genetic analysis of prairie and montane populations of Dermacentor andersoni (Stiles) originating from Alberta (AB) and British Columbia (BC), Canada, respectively, indicated limited gene flow (N_m < 1) and a large amount of genetic differentiation (F_st = 0.49) between the populations. The prairie population also had a greater level of genetic diversity. Mating experiments indicated that females of geographically heterogeneous crosses had similar engorgement and oviposition failure as homogenous crosses in the parental generation but that egg mass sterility was greatest for the AB♀ × BC♂ cross, intermediate for the homogenous crosses, and lowest for the BC♀ × AB♂ cross. The progeny of all crosses produced fertile eggs, and the only significant effect in the progeny generation was increased oviposition failure of the pure AB cross. Covariate analysis indicated that egg mass sterility was associated with BC males in the parental generation and that oviposition failure was associated with AB males and AB females in the progeny generation. The hazard of cumulative reproductive failure was increased with AB females in both generations, reduced for AB males in the parental generation, and increased with AB males in the progeny generation. Overall, heterogenous crosses had the greatest and least reproductive failure in the parental generation, but they were intermediate to the homogenous crosses in the progeny generation. The limited gene flow between the populations seems to have been sufficient to maintain reproductive compatibility.

Apoptosis (programmed cell death) is a tightly regulated physiological process. The inhibitors of apoptosis proteins (IAPs) are key regulators for apoptosis. An inhibitor of apoptosis protein gene IAP1 was recently cloned from Aedes aegypti (L.) (AaeIAP1, GenBank accession no. DQ993355); however, it is not clear whether AaeIAP1 is developmentally and environmentally regulated. In this study, we applied quantitative polymerase chain reaction (PCR) to investigate the expression levels of the AaeIAP1 transcript in different developmental stages and under different environmental conditions. Our results revealed that the expression of the AaeIAP1 transcript was detectable in all life stages of Ae. aegypti, with significantly higher levels in pupal and adult stages than in larval stages. Furthermore, when Ae. aegypti was exposed to all stressful environmental conditions (e.g., low and high temperatures, UV radiation, acetone, and permethrin insecticide treatment), the expression level of AaeIAP1 transcript was increased significantly. Our results suggest that AaeIAP1 might play an important role in both the physiological development of Ae. aegypti and stress-induced apoptosis.

The essential oil of catmint, Nepeta cataria L., was hydrogenated to yield an oil enriched in dihydronepetalactone (DHN) diastereomers, termed. This material was used for the preparation of liquid alcohol–based and lotion formulations. The efficacy of these formulations as repellents was tested after application to human test subjects at two locations in the United States: Maine and Florida. In Maine, data on repellency of the hydrogenated catmint oil formulations toward black flies (Simulium decorum Walker) and mosquitoes (primarily Aedes intrudens Dyar) were obtained. In these tests, protection from black flies was conferred for 6 h or more with all formulations, and both liquid and lotion formulations at 15 wt% active ingredient gave complete protection for 7.5 h. All formulations conferred protection from mosquitoes for >4 h, with the best (15 wt% lotion) giving >8 h of complete protection. In Florida, data on repellency toward a mixed population of mosquitoes indicated that all formulations conferred protection for >4 h, with the 15 wt% lotion giving >6 h complete protection from bites.

A field trial to assess the efficacy of Bistar 80 SC as a barrier treatment of Australian military tents was conducted over 10 d at Mount Bundey Military Training Area, Northern Territory, Australia, in March 2003. Four pairs of standard eight-person tents were erected, with a single tent in each pair treated with 0.1% Bistar 80 SC as a course spray, and the remainder left as untreated control tents. Carbon dioxide-baited traps were operated in each tent nightly, and biting collections conducted over 8 nights. There was a mean increase in protection of 81% for mosquitoes entering treated tents and 90.4% increase in protection against biting of predominantly Culex annulirostris Skuse. In addition, bifenthrin applied to the military tents enhances the protection of occupants against bites from this important arbovirus vector.

This study establishes deltamethrin resistance in a common bed bug, Cimex lectularius L., population collected from New York City (NY-BB). The NY-BB population was 264-fold more resistant to 1% deltamethrin in contact bioassay compared with an insecticide-susceptible population collected in Florida (FL-BB). General esterase, glutathione S-transferase, and 7-ethoxycoumarin O-deethylase activities of NY-BB were not statistically different from those of FL-BB. cDNA fragments that encoded the open reading frame of voltage-sensitive sodium channel α-subunit genes from the FL-BB and NY-BB populations, respectively, were obtained by homology probing polymerase chain reaction (PCR) and sequenced. Sequence alignment of the internal and 5′ and 3′ rapid amplification of cDNA ends (RACE) fragments generated a 6,500-bp cDNA sequence contig, which was composed of a 6,084-bp open reading frame (ORF) encoding 2,027 amino acid residues and 186-bp 5′ and 230-bp 3′ untranslated regions (5′ and 3′ UTRs, respectively). Sequence comparisons of the open reading frames of the α-subunit genes identified two point mutations (V419L and L925I) that were presented only in the NY-BB population. L925I, located the intracellular loop between IIS4 and IIS5, has been previously found in a highly pyrethroid-resistant populations of whitefly (Bemisia tabaci). V419L, located in the IS6 transmembrane segment, is a novel mutation. A Val to Met mutation at the corresponding position of the bed bug V419, however, has been identified in the tobacco budworm as a kdr-type mutation. This evidence suggests that the two mutations are likely the major resistance-causing mutations in the deltamethrin-resistant NY-BB through a knockdown-type nerve insensitivity mechanism.

The fat body is the intermediary metabolism organ of insects and the main source of hemolymph components. In the current study, the microanatomy of Aedes aegypti (L., 1762) fat body was studied through scanning electron microscopy to observe the effects of blood feeding and aging. Three groups of female mosquitoes were used: newly emerged females, 18-d-old sugar-fed females, and 18-d-old blood-fed females. In Ae. aegypti, the fat body is located beneath the integument, and it is subdivided into dorsal, ventral, and lateral lobes, with the latter two being larger than the dorsal lobes. The lobes projected into the body cavity, and they were covered externally by a basal lamina with rounded cells beneath it. In 18-d-old sugar-fed females, the ventral and dorsal fat bodies seemed more developed than in newly emerged mosquitoes. The fat body hypertrophy caused by aging in the sugar-fed mosquito was probably associated with lipid accumulation due to the sugar diet. The blood-fed 18-d-old mosquitoes showed flattened fat bodies in all locations. The fat body modifications after the blood ingestion may be associated with midgut expansion after blood feeding, followed by ovary hypertrophy that mechanically compresses the fat body against the body wall. The structural changes in the fat body after a bloodmeal may be important for midgut extension to maximize blood storage and subsequent ovary enlargement, leading to the organ’s reorganization in the body cavity. In addition, the depletion of fat body content during vitellogenesis could be responsible for the shrinking and flattening of the fat body lobes.

Francisella tularensis, a potential bioterrorism agent, is transmitted by arthropod vectors and causes tularemia in many mammals, including humans. Francisella novicida causes disease with similar pathology in mice. We show that F. novicida invades hemocyte-like cells of the Sua1B cell line derived from Anopheles gambiae and replicates vigorously within these cells. We used transposon knockouts of single genes of F. novicida to show that bacterial growth within these insect cells is dependent on virulence factors encoded in a bacterial pathogenicity island that has been linked to replication in mammalian macrophages. The virulence factors MglA, IglA, IglB, IglC, and IglD as well as PdpA and PdpB were necessary for efficient growth in insect cells, but PdpC and PdpD were not required. The Sua1B cell line presents a valuable model to study the interactions between this important pathogen and insect vectors.

To test the hypothesis that enzootic and epidemic Venezuelan equine encephalitis (VEE) complex alphaviruses can infect and be transmitted by Ae. aegypti, we conducted a series of experimental infection studies. One set of experiments tested the susceptibility of geographic strains of Ae. aegypti from Peru and Texas (USA) for epidemic (subtype IC) and enzootic (subtype ID) strains from Colombia/Venezuela, whereas the second set of experiments tested the susceptibility of Ae. aegypti from Iquitos, Peru, to enzootic VEE complex strains (subtypes ID, IIIC, and IIID) isolated in the same region, at different infectious doses. Experimental infections using artificial bloodmeals suggested that Ae. aegypti mosquitoes, particularly the strain from Iquitos, Peru, is moderately to highly susceptible to all of these VEE complex alphaviruses. The occurrence of enzootic VEE complex viruses circulating endemically in Iquitos suggests the possibility of a dengue-like transmission cycle among humans in tropical cities.

Since the invasion of California by West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in 2003, we have annually monitored vector competence for the NY99 strain in Culex tarsalis Coquillett, Culex pipiens quinquefasciatus Say, Culex p. pipiens L., and Culex stigmatosoma Dyar populations from four areas: deserts of Coachella Valley, densely urbanized maritime Los Angeles, southern San Joaquin Valley in Kern County, and southern Sacramento Valley near Davis in Sacramento County. Overall, Cx. stigmatosoma was the most competent vector species, followed by Cx. tarsalis and the Cx. pipiens complex. The median infectious dose (ID₅₀) of WNV required to infect 50% of the F1 female progeny reared from wild-caught females, a measure of mesenteronal susceptibility, ranged between 5 and 8 log₁₀ plaque forming units/ml and was not correlated with annual human case incidence or summer maximum likelihood mosquito infection estimates. Odds ratios comparing nonoutbreak years with referent outbreak years were variable and failed to show a distinct pattern for Cx. tarsalis or Cx. pipiens complex females. Apparently factors other than midgut susceptibility within the ranges we measured enabled WNV outbreaks in California. Culex populations remained competent for St. Louis encephalitis virus, indicating that the disappearance of this virus was not related to a loss of vector competence.

In total, 1,500 specimens (448 males and 1,052 females) of the flea Ctenocephalides felis felis (Bouché) (Siphonaptera: Pulicidae) were collected over a period of a year from 150 dogs captured by the Centro de Controle de Zoonoses de Belo Horizonte, Minas Gerais, Brazil. Microscopic examination of the dissected fleas revealed that 180 fleas were infected with a species of gregarine that was subsequently identified as a member of the genus Steinina. The relative abundances, prevalence rates, and seasonal variation of the different developmental stages of this endoparasite in C. felis felis were determined. Both gamonts and gametocysts presented significant seasonal variation.

We evaluated the blood-feeding patterns in several mosquito species that may serve as vectors of disease agents in the northeastern United States. Blood-fed mosquitoes were collected from 91 different sites throughout Connecticut over a 6-yr period (June–October 2002–2007), and the host-feeding patterns of 23 mosquito species representing six genera were examined by using a polymerase chain reaction-based assay and sequencing portions of the cytochrome b gene of mitochondrial DNA. This study was part of a statewide surveillance program and for some of the mosquito species a limited number of specimens were examined [e.g., Aedes communis (De Geer) (1), Anopheles barberi Coquillett (1), Uranotaenia sapphirina (Osten Sacken) (5)]. With the exception of Culex territans Walker that acquired bloodmeals from all four classes of vertebrates—birds, reptiles, amphibians, and mammals—all species of Aedes, Anopheles, Coquillettidia, Psorophora, and to a lesser degree, Uranotaenia, were found to feed predominately upon mammalian hosts. Fourteen mammalian species were identified as sources of blood, but the majority of feedings were taken from the white-tailed deer, Odocoileus virginianus. Human-derived bloodmeals were identified from 13 of the 23 mosquito species. Limited avian-derived bloodmeals were detected in Aedes canadensis (Theobald), Aedes cantator (Coquillett), Aedes cinereus Meigen, Aedes triseriatus (Coquillett), Aedes trivittatus (Coquillett), Coquillettidia perturbans (Walker) Cx. territans, Psorophora ferox (von Humboldt), and Ur. sapphirina. American robin, Turdus migratorius, was the most common source of avian blood, followed by a few other mostly Passeriformes birds. We conclude that the white-tailed deer serve as the main vertebrate host for these mammalophilic mosquitoes in this region of the United States. This feeding pattern supports enzootic amplification of arboviruses, including Jamestown Canyon, Cache Valley, and Potosi viruses that perpetuate in cervid hosts. Occasional feeding on avian hosts suggests that some of these mosquito species, such as Cq. perturbans, also could facilitate transmission of West Nile and eastern equine encephalitis viruses from viremic birds to mammalian hosts.

The tropical horse tick, Dermacentor nitens, is a natural vector of Babesia caballi in the Americas. B. caballi, one of the etiologic agents of equine piroplasmosis, occurs widely throughout the world, but the United States and a few other countries are considered to be free of infection. B. caballi is transovarially transmitted by the one-host tick D. nitens; we tested the hypothesis that B. caballi can persist in multiple generations of D. nitens in the absence of opportunity to reacquire infection from a susceptible equine host. Partially engorged female D. nitens were collected from a B. caballi–infected horse in Puerto Rico and allowed to reattach and feed on an uninfected horse, successfully transmitting the infection. Three subsequent generations of ticks were reared on calves (nonsusceptible hosts for B. caballi), testing for B. caballi infection in each generation by feeding a sample of the larvae on naïve horses. The first generation of D. nitens reared on a nonsusceptible host transmitted B. caballi, whereas the second and third failed to transmit to naïve horses, showing that D. nitens infection with B. caballi was restricted to one generation in the absence of alimentary reinfection. These results imply that, in the event of the introduction of this pathogen into areas of the continental United States where D. nitens occurs, the tick could become a short-term reservoir of B. caballi, making control of introduced infections more complex.

The current study compared the susceptibility of larval stages of Amblyomma cajennense (F.), Amblyomma aureolatum (Pallas), and Rhipicephalus sanguineus (Latreille) to infection by a Brazilian strain of Rickettsia rickettsii. Guinea pigs experimentally infected by R. rickettsii were simultaneously infested by larvae of the three tick species. Recovered engorged larvae were allowed to molt to nymphs and held in an incubator at 23°C and 85–90% RH. Subsequent flat nymphs were tested for rickettsial infection by polymerase chain reaction (PCR). Concomitant infestations with sibling ticks on noninfected guinea pigs (control) were done. While 10–60% of the A. cajennense nymphs were shown to be infected by R. rickettsii, both A. aureolatum and R. sanguineus were highly susceptible to R. rickettsii, since 80–100% of their nymphs were shown to be infected in the corresponding trials. Most of the engorged larvae (≈70–95%), regardless of being infected or not, successfully molted to nymphs. Mortality rates for engorged larvae tended to be statistically similar (P > 0.05) for ticks recovered from R. rickettsii-infected and noninfected guinea pigs, within each tick species. The only exceptions were the significantly higher mortalities (P < 0.05) for engorged A. cajennense larvae recovered from two infected guinea pigs. Therefore, A. cajennense was less susceptible to R. rickettsii infection than A. aureolatum and R. sanguineus, while feeding on rickettsemic guinea pigs. These two later species were similarly highly susceptible.

The role of deer mice and other species of Peromyscus as enzootic reservoirs for plague remains controversial. In this study, we evaluated early-phase vector efficiency of Aetheca wagneri Baker, a common flea species infesting deer mice, to determine the likelihood that Y. pestis could be spread mouse to mouse by this species. We showed that A. wagneri could transmit plague bacteria to laboratory mice as early as 3 d postinfection (p.i.), but transmission efficiency was quite low (1.03%; 95% CI: 0.19–3.34%) 1–4 d p.i. compared with that for the established plague vector Oropsylla montana Baker (10.63%; 95% CI: 4.18–25.91). Using this early-phase transmission efficiency estimate, we determined through parameterization of a simple predictive model that at least 68 A. wagneri per deer mouse would be required to support levels of transmission adequate for enzootic maintenance. Because deer mice typically harbor fewer than three A. wagneri per host, our data do not support the notion of an independent deer mouse–A. wagneri transmission cycle.

This study was conducted as part of a field-ecology study of arboviral and malarial activity in the Amazon Basin, Loreto Department, Peru, to determine the relative abundance, species diversity, and seasonal and vertical distributions of potential mosquito vectors. Mosquitoes were captured either by volunteers using mouth aspirators while mosquitoes attempted to land on the collectors or in dry ice–baited ABC light traps. Anopheles darlingi, the principal malaria vector in the region, was the most commonly captured anopheline mosquito in Puerto Almendra village (99%) while landing on humans, with a mean of 37.1 mosquitoes captured per 24-h period, representing nearly one half of all mosquitoes collected. An. darlingi human landing activity began shortly after sunset, peaked at 2000–2100 hours, and declined gradually until sunrise. This species readily entered houses, because 51% of the An. darlingi captured by paired collectors, stationed inside and outside houses, were captured indoors. Human landing collections provided a more accurate estimate of human attraction of An. darlingi, capturing 30 times as many as co-located dry ice–baited ABC light traps. In contrast, eight times as many Culex (Melanoconion) species, including known arbovirus vectors, were captured in light traps as by co-located human collectors. Despite being located within 300 m of the village collection site, only a few Anopheles species were captured at the forest collection site, including only 0.1 An darlingi/24 h, thus indicating that An. darlingi activity was directly associated with the rural village. These data provide a better understanding of the taxonomy, population density, and seasonal distribution of potential mosquito vectors of disease within the Amazon Basin region and allow for the development of appropriate vector and disease prevention strategies that target vector populations.

New approaches for control of the dengue vector Aedes aegypti (L.) are being developed, including the potential introduction of life-shortening symbiont bacteria into field populations and the release of transgenic strains with reduced vector competency. With these new approaches comes the need for rapid estimations of existing field population size. Here, we describe the use of simulation modeling with container-inhabiting mosquito simulation (CIMSiM) for estimation of Ae. aegypti pupal crop size in north Queensland, Australia. CIMSiM was calibrated for local conditions by deploying “sentinel key containers” (tire, 2-liter plastic bucket, 0.6-liter pot plant base, and tarpaulin indentation) in which water flux and pupal productivity were studied for 72 d. Iterative adjustment of CIMSiM parameters was used to fit model outputs to match that of sentinel key containers. This calibrated model was then used in a blind field validation, in which breeding container and local meteorological data were used to populate CIMSiM, and model outputs were compared with a field pupal survey. Actual pupae per ha during two 10-d periods in 2007 fell within 95% confidence intervals of simulated pupal crop estimates made by 10 replicate simulations in CIMSiM, thus providing a successful field validation. Although the stochasticity of the field environment can never be wholly simulated, CIMSiM can provide field-validated estimates of pupal crop in a timely manner by using simple container surveys.

Tsetse flies are the cyclic vectors of sleeping sickness and African animal trypanosomosis. The possibility to classify the natural habitat of riverine tsetse species is explored in the Mouhoun River basin, Burkina Faso: the objectives were to discriminate the riverine forests community types and their fragmentation levels by using Landsat 7 enhanced thematic mapper images, to map tsetse densities. Glossina palpalis gambiensis Vanderplank 1949 (Diptera: Glossinidae) and G. tachinoides Westwood, 1850 are the vectors of trypanosomoses in this area. After a supervised classification, the community types were discriminated using the water area in 400-m-wide polygons around the river. A fragmentation analysis of the swamp forest unit, cross-tabulated with the community types, lead to identification of the final landscapes where tsetse apparent densities (ADT) were implemented using a training data set of 608 trap locations. The predicted ADT were then compared with an independent validation data set of 78 trap locations. The correlation between the model predictions and the validation data set was high, validating this approach (P < 0.001). The riverine forest community type and fragmentation level are critical factors for riverine tsetse species, which should be taken into consideration to map their suitable habitat.

A new strain of Culex flavivirus (family Flaviviridae, genus Flavivirus, CxFV), an insect virus first described in Japan, was isolated from adult Culex quinquefasciatus Say (Diptera: Culicidae) collected in 2006 from Izabal Department on the Caribbean coast of Guatemala. Mosquito pools were assayed for flavivirus RNA by using flavivirus group-specific primers that amplified a 720-bp region of the nonstructural (NS) 5 gene by standard reverse transcriptase-polymerase chain reaction. From 210 pools (1,699 mosquitoes), eight tested positive, and six of these mosquito pools produced virus isolates in Aedes albopictus Skuse C6/36 cells. Nucleotide sequence comparison of the eight flavivirus RNA-positive pools showed that there was 100% identity among them, and phylogenetic analysis of the NS5 and envelope gene regions indicated that they represent a strain of the recently described CxFV from Japan. This is the first report of an insect flavivirus from Central America.