The susceptibility of tsetse flies (Diptera: Glossinidae), Glossina palpalis gambiensis (Vanderplank), and G. m. morsitans (Westwood) to topically applied spinosad, a mixture of insecticidal molecules from the actinomycete Saccharopolyspora spinosa, is almost as high as to deltamethrin. However, susceptibility to spinosad does not differ significantly between teneral and gravid flies, contrary to deltamethrin. Spinosad might be a promising candidate for future tsetse control by the sequential aerial technique.

The patterns of exochorion ornaments on eggs of seven South American Lutzomyia sand fly species were analyzed by scanning electron microscopy (SEM): Lutzomyia (Lutzomyia) cruzi (Mangabeira 1938), Lutzomyia (Micropygomyia) evandroi (Costa Lima and Antunes 1936), L. (Nyssomyia) intermedia (Lutz and Neiva 1912), L. longipalpis (Lutz and Neiva 1912), L. migonei (França 1920), L. (Nyssomyia) neivai (Pinto 1926), and L. renei (Martins, Falcão, and Silva 1957). Different patterns were observed, which showed the distinction between some species. Egg ornaments in L. cruzi and L. longipalpis appear as single, parallel, unconnected ridges, whereas eggs of L. migonei appear as single, parallel, connected ridges. Eggs of L. (Nyssomyia) intermedia and L. (N.) neivai present a new variation of the single, unconnected, parallel ridges pattern: small tubercles are present, distributed between the ridges. Eggs of L. renei present an elliptical pattern, with most structures connected by straight ridges. Eggs of L. (M.) evandroi present a polygonal pattern, with alternate rows of small and large hexagons. Our data emphasize the advantages of the SEM approach in the study of the exochorion patterns of Lutzomyia eggs and in the distinction of the sand fly species.

Using ecoethology of bats and statistical methods, we anticipate the evidence of specific species of spinturnicids associated with Myotis myotis and Myotis bechsteinii (Chiroptera, Vespertilionidae) mixed colonies are unknown. Traditional description of this new crpytic species Spinturnix bechsteini, parasite of M. bechsteinii, is done. Statistical approach is based on analysis of variance and principal component analysis. The current knowledge on parasites of the genus Myotis in the West Palearctic subregion is presented.

A new species of phlebotomine sand fly, Lutzomyia emberai n. sp, is described and illustrated from specimens collected in a dwelling of the Emberá Indian community, situated in the foothills of the Serranía del Baudó on the Colombian Pacific coast. The morphological characteristics of L. emberai n. sp. suggest that it belongs to the series pia of the group verrucarum, easily differentiated from the other members of this group by diagnostic characters on the palps, labro-pharynx, thorax, and spermathecal ducts. The discovery of this new phlebotomine raises to seven the number of species in the series pia, including Lutzomyia pia (Fairchild & Hertig, 1961); Lutzomyia reclusa Fernandez & Rogers, 1991; Lutzomyia suapiensis Le Pont, Torrez-Espejo & Dujardin, 1997; Lutzomyia tihuiliensis Le Pont, Torrez-Espejo & Dujardin, 1997; Lutzomyia tocaniensis Le Pont, Torrez-Espejo & Dujardin, 1997; Lutzomyia limafalcaoae (Wolff & Galati, 2002); and Lutzomyia emberai Bejarano, Duque & Velez, 2004, n. sp. The taxonomy, distribution, and medical importance of this series are reviewed.

The blacklegged tick, Ixodes scapularis Say, a vector for the agents of Lyme borreliosis and other diseases, has expanded its range dramatically over the past 20 yr. However, the relative contributions of different vertebrate host species to this expansion have remained largely unexplored. To address this issue, we simulated the expansion of a theoretical tick population across a simple landscape by using a deterministic, spatially explicit, cellular automata model. The model incorporates the ecology of ticks and three vertebrate hosts: white-tailed deer, Odocoileus virginianus Zimmermann; white-footed mouse, Peromyscus leucopus Rafinesque; and American robin, Turdus migratorius L. Host contribution to tick dispersal is modeled as a function of tick burden, home range size, and population density. These parameters were determined using published and unpublished data. Our results suggest that 1) hosts with high tick burdens and large home ranges (e.g., deer) play a critical role in I. scapularis range expansion; 2) hosts with small home ranges (e.g., mice) can limit range expansion if they divert a sufficient number of ticks from feeding on more mobile hosts; and (3) birds that migrate annually (e.g., robins) can play a crucial role in tick range expansion.

Diel feeding activity of third and fourth instars of Anopheles quadrimaculatus Say were studied in a Michigan permanent pond. This field study examined the consumption of microbial and microinvertebrate food resources over a diel (24-h) period between two habitats (open water and vegetated areas). A fluorochromatic stain (4,6-diamidino-2-phenylindole) was used to quantify microbial dietary components within larval guts and habitats. Microbial analyses show that bacteria were the most abundant food type, followed by detritus, algae, and invertebrate parts/protozoans (IPP). Larval consumption of cladocerans was significantly greater at midnight than noon. Larval gut analyses examined every hour over a 24-h period provided significant evidence as to the approximate time larvae switch microinvertebrate dietary resources. Habitat had a significant effect on microinvertebrate consumption by An. quadrimaculatus larvae. Larvae consumed more water mites and rotifers in the open water areas than vegetated zones. We found that An. quadrimaculatus larvae do not preferentially feed on microinvertebrates over a diel period, however, larvae may feed selectively on rotifers in open water habitats. Knowledge of the “feeding area” or microhabitats, with respect to where and when larvae optimally forage as well as particle sizes and food types consumed in the natural habitats will enhance the success of bacteria and other particulate larvicides.

Spatial patterns of Ixodes scapularis Say, the vector of the Lyme disease agent, have been examined at various geographic scales, demonstrating that distributions of these ticks are spatially autocorrelated at both national and state scales. We tested the hypothesis that distributions of nymphal I. scapularis ticks at the fine scale of an endemic community also are spatially autocorrelated. Nymphal tick densities were determined by collecting ticks from 51 and 47 wooded residential properties in a southern Rhode Island town in 2002 and 2003, respectively. The average tick density at residences during 2002 was 51.17 (± 46.04) nymphs per hour, with a range of 3–297 and median of 40.82. In 2003, the average tick density was 44.48 (± 38.31) nymphs per hour, with a range of 3–153 and median of 36. Semivariance analysis revealed no spatial autocorrelation in tick densities between residences, likely due to the high variability of tick distributions at this scale. Further analysis of drag-sampling data at individual residences by using Lloyd’s patchiness index (m*/m) demonstrated a patchy distribution of nymphs. High variability of nymphal I. scapularis densities may greatly affect predicting spatial patterns of ticks at a fine scale.

Heat and vibration are common host-generated cues that ectoparasites use to orient to hosts. Three experiments evaluated effects of heat and vibration on the movement of northern fowl mite, Ornithonyssus sylviarum (Canestrini & Fanzago). Individual arrested mites in an isolation chamber always initiated movement (walking) after substrate vibration (7.8-min walking duration), but only initiated movement 50% of the time (2.8-min walking duration) upon exposure to a 3°C heat fluctuation. Heat fluctuation in combination with vibration extended the period of activity by ≈50% (11.6-min walking duration) compared with activity initiated by vibration alone. Mites with longer time off-host moved for shorter durations. In a choice test, individual mites consistently moved closer to a 35°C heat source 1 or 6 mm away, but not to a heat source 11 mm away. In a circular arena, mites were able to orient accurately to a 35°C heat source and reached the arena edge almost 4 times faster (11.2 s) than mites without a heat source (41.2 s). These results suggest that northern fowl mite is capable of directed thermo-orientation, as well as modulation of activity depending on the type of sensory information perceived. The adaptive significance of this orientation for a “permanent” ectoparasite is discussed.

A new automatic device for recording the host-seeking behavior of mosquitoes was designed using photoelectric sensors. The host-seeking rhythms of several species of mosquitoes were recorded under laboratory conditions. Use of CO₂, in addition to heating and black color to activate mosquito flight, proved to be important for evaluation of the present recording device. The diel rhythms of nonblood-fed Aedes albopictus (Skuse), Aedes aegypti (L.), Culex quinquefasciatus Say, Culex tritaeniorhynchus Giles and Anopheles stephensi Liston females recorded by the device corresponded well with known flight and activity rhythms in field for the same mosquito species. This simple automatic recording device provided accurate information on the flight behaviors of colonized and field collected mosquitoes.

The population genetics of Triatoma dimidiata (Latreille, 1811) from five different provinces in Guatemala, including three sylvan and three domestic populations, was investigated by random amplification of polymorphic DNA-polymerase chain reaction. There is a high degree of genetic variation in all of the T. dimidiata populations as evidenced by high levels of average expected heterozygosity and polymorphism. Domestic populations are more closely related to each other (D = 0.05–0.085, Nei’s genetic distance) than are the sylvan (D = 0.121–0.189). Within the limited sample size of three populations, there was a correlation with geographic and genetic distance for the domestic populations, but not for the sylvan. Surprisingly, one of the sylvan populations was genetically very similar to the domestic populations. The F_ST demonstrated a high degree of differentiation at the country-wide level (F_ST = 0.175) and a moderate degree of differentiation within the sylvan (F_ST = 0.135) or domestic (F_ST = 0.097) populations. Although these results demonstrated that gene flow is limited between different provinces in Guatemala, hierarchical analysis showed that barriers between the Atlantic and Pacific drainage slopes were not biologically significant limiters of gene flow.

Complexes of sibling species are common among mosquitoes, and their existence within vector species can have important epidemiological consequences. Anopheles albitarsis sensu stricto and Anopheles deaneorum Rosa-Freitas are two putative vectors of malaria parasites belonging to the Albitarsis species complex (Diptera: Culicidae). Using an induced mating technique, we studied the reproductive isolation between these two closely related species and their reciprocal hybrids. Evidence for hybrid male sterility consistent with Haldane’s rule was found. The results indicate that male hybrids show very low insemination rates, probably due to abnormalities in their reproductive organs. In addition, the data show that hybrid males carrying an X chromosome derived from An. deaneorum perform significantly worse than hybrid males carrying an An. albitarsis s.s. X chromosome.

Prior studies have identified a complicated pattern of interspecific hybridization between members of the Aedes (Stegomyia) scutellaris (Walker) mosquito group, which includes medically important vectors of bancroftian filariasis and dengue. Here, we report that two members of the group, Aedes polynesiensis Marks and Aedes riversi Bohart & Ingram, are both infected with intracellular Wolbachia bacteria. Sequencing of the Wolbachia wsp gene demonstrates that the infections differ from each other and from Wolbachia infections previously reported in mosquitoes. Aedes polynesiensis is the first mosquito identified with a wMel Wolbachia type. Intraspecific crosses of infected and aposymbiotic lines generated via antibiotic treatment show that the Wolbachia infections in both species cause high levels of cytoplasmic incompatibility. Interspecific crosses show that the two species are reproductively isolated. However, repeating the interspecific crosses with aposymbiotic mosquito strains demonstrates that the Wolbachia infections play a role in preventing hybrid offspring. We discuss Wolbachia infections in relation to better defining the evolutionary relationships and causes of speciation within the group, understanding the basis for the observed east-to-west gradient in filarial refractoriness, and developing novel genetic control measures.

An entomological survey was conducted on vectors of malaria in a village of the forest–savannah transition area in Cameroon from February 1999 to October 2000. A total of 2,050 anopheline mosquitoes belonging to eight species were caught 1) after landing on human volunteers, 2) by using pyrethrum spray collections in human dwellings, and 3) in resting sites outdoors. Anopheles funestus Giles was the most abundant species (accounting for 91% of anophelines caught) followed by Anopheles gambiae Giles (7%). Applying polymerase chain reaction led to the identification of all specimens of the An. funestus group as An. funestus sensu stricto and mosquitoes from the An. gambiae complex were mostly An. gambiae sensu stricto of the S molecular form. Malaria transmission was perennial with an entomological inoculation rate estimated at 172 infective bites per person during the period of study. An. funestus was responsible for 88% of the total malaria transmission, with a Plasmodium falciparum circumsporozoïte rate of 6.8% and an anthropophilic rate of 99.3%. These results confirm that in high agricultural activity areas, An. funestus can be, by far, the major malaria vector.

The sand fly Lutzomyia longipalpis Lutz & Neiva (Diptera: Psychodidae: Phlebotominae), the main vector of Leishmania infantum in the Americas, is believed to be a species complex, although the status of different Brazilian populations is still somewhat unclear. Preliminary analysis of the acoustic signals that are produced during copulation by L. longipalpis males has suggested the existence of three sibling species in Brazil. In the current report, we analyze in more detail a number of parameters of the copulatory courtship songs of L. longipalpis males from four allopatric populations from different parts of the country (Marajó Island, Natal, Jacobina, and Lapinha Cave) and from two sympatric populations from the locality of Sobral, where two types of males can be differentiated by the number of pale spots (one or two pairs) found on the abdomen. We show that males from the localities of Natal, Marajó, and Sobral (two-spot morph) have very similar songs composed of successive bursts, which are modulated in frequency and amplitude. No significant differences were found in the song parameters of these three populations. In contrast, one-spot males from Sobral and males from Jacobina and Lapinha produce songs that are made of pulses but with distinct patterns for each population and significant differences in all song parameters studied. The results suggest that the L. longipalpis complex in Brazil is composed of four sibling species and that the differences in song patterns between the populations are consistent with the level of divergence found in the period gene.

In 2000, 22,000 French military personnel were deployed overseas. The French military health service implemented a vector control strategy including personal protection by the use of permethrin preimpregnated battlefield uniforms (BFUs) and the application on the skin of a topical repellent (50% DEET). In 2000, French forces used an industrial process to impregnate cloth with permethrin by soaking it before cut-out of the BFU. A study was implemented in four experimental huts in Côte d’Ivoire to assess the field efficacy of the impregnated BFUs and their resistance to washing. Taking into account the systematic variations in each variable in the field and using a modeling based on logistic regression and discriminant analysis, this study showed that after 6 h without reapplication, the protective effects of the use of DEET as skin repellent was not significant, perhaps due to the high density of Anopheles mosquitoes during the night catching sessions and an average time of effective repellency of <2 or 3 h in the field. The analysis also showed that the French process of industrial impregnation of permethrin of the BFU offered in 2000 some protection from mosquito bites but not enough to reduce significantly the incidence of malaria among nonimmune troops. No positive or negative interaction was noted when DEET and the impregnated BFUs were used together.

Ixodes scapularis Say adults, nymphs, and larvae were treated with the entomopathogenic fungus Metarhizium anisopliae in a combination of field and laboratory experiments to assess sublethal effects of the fungus on I. scapularis fecundity and body mass. Postengorgement and egg mass weights were 33 and 50% lower, respectively, in adult females treated with M. ansiopliae in the field before engorging on laboratory rabbits. M. anisopliae did not significantly reduce egg mass weight, conversion efficiency, or oviposition period in I. scapularis females treated with the fungus after engorging on white-tailed deer, although only 33% of treated females oviposited. Engorged nymphs and larvae treated with M. anisopliae converted significantly lower percentages of their engorged weight to their molted adult and nymphal weights. This study indicates that M. anisopliae reduces fitness (fecundity and body mass) in all active I. scapularis stages and indicates that its impact as a biocontrol agent might be higher than that suggested by direct mortality alone.

Resistance management for insecticide-treated nets (ITNs) remains a challenge. Options are limited, because a safe and highly active insecticide with a persistence of several months is required. These criteria have only been met by pyrethroids, although organophosphates (OPs) and carbamates have been considered as alternatives for impregnation of eave curtains. It has been observed that some pyrethroid-resistant mosquito strains show increased OP susceptibility over pyrethroid-susceptible strains (i.e., negative cross-resistance). The current study investigated whether this phenomenon applies to a range of mosquito species and strains, because a mixture or rotation strategy for resistance management could then be envisaged. Adult female mosquitoes from laboratory strains of Anopheles stephensi Liston, Anopheles gambiae Giles, and Culex quinquefasciatus Say were tested in World Health Organization susceptibility test kits. For An. stephensi, the highly pyrethroid-resistant DUB 234 strain showed the same level of resistance to malathion as the pyrethroid-susceptible DUB S. The malathion-resistant ST MAL strain was as susceptible to pyrethroids as the insecticide-susceptible BEECH. For An. gambiae, the malathion tolerance of the previously pyrethroid-resistant RSP strain was significantly higher than that of the insecticide-susceptible KWA. For Cx. quinquefasciatus, selection of the QUINQ strain with permethrin abolished preexisting resistance to the OP malathion as pyrethroid resistance increased, rendering the strain more susceptible to malathion than PEL SS. Some indication of negative cross-resistance to malathion was found for the permethrin-resistant MUHEZA strain. The occurrence of negative cross-resistance seems dependent on the history of insecticide selection and is not generally applicable. Resistance management for ITNs will need to use mechanisms other than negative cross-resistance to be effective.

Synergistic interactions among the multiple endotoxins of Bacillus thuringiensis subsp. israelensis de Barjac play an important role in its high toxicity to mosquito larvae and the absence of insecticide resistance in populations treated with this bacterium. A lack of toxin complexity and synergism are the apparent causes of resistance to Bacillus sphaericus Neide in particular Culex field populations. To identify endotoxin combinations of the two Bacillus species that might improve insecticidal activity and manage mosquito resistance to B. sphaericus, we tested their toxins alone and in combination. Most combinations of B. sphaericus and B. t. subsp. israelensis toxins were synergistic and enhanced toxicity relative to B. sphaericus, particularly against Culex quinquefasciatus Say larvae resistant to B. sphaericus and Aedes aegypti (L.), a species poorly susceptible to B. sphaericus. Toxicity also improved against susceptible Cx. quinquefasciatus. For example, when the Cyt1Aa toxin from B. t. subsp. israelensis was added to Bin and Cry toxins, or when native B. t. subsp. israelensis was combined with B. sphaericus, synergism values as high as 883-fold were observed and combinations were 4–59,000-fold more active than B. sphaericus. These data, and previous studies using cytolytic toxins, validate proposed strategies for improving bacterial larvicides by combining B. sphaericus with B. t. subsp. israelensis or by engineering recombinant bacteria that express endotoxins from both strains. These combinations increase both endotoxin complexity and synergistic interactions and thereby enhance activity and help avoid insecticide resistance.

Female white-tailed deer, Odocoileus virginianus (Zimmerman), were held in small pens and administered doramectin by free choice of doramectin-coated whole kernel corn, Zea mays L., fed ad libitum with 19% protein deer pellets also being fed ad libitum in a separate container. The mean concentration of doramectin in the serum during treatment was 72.8 ppb. The mean doramectin concentration in the serum decreased to <2 ppb, the lower limit of detection by high-pressure liquid chromatography, by day 14 after termination of treatment after withdrawal of doramectin-treated corn from the diet.

The susceptibility of four strains of Aedes albopictus (Skuse) to permethrin, deltamethrin, resmethrin, chlorpyrifos, malathion, propoxur, fipronil, imidacloprid, spinosad, and Bacillus thuringiensis variety israelensis (Bti) was determined. The HAmAal and MAmAal strains were collected in 2002 and 2003, respectively, from Huntsville and Mobile, AL, and the VBFmAal and SFmAal strains were collected in 1998 from Vero Beach and southern Florida, respectively. The HAmAal strain showed a 22-fold elevated level of resistance to deltamethrin compared with the susceptible Ikaken laboratory strain, whereas the VBFmAal strain showed a six-fold lower sensitivity to deltamethrin compared with Ikaken. However, comparison of resistance ratios for deltamethrin at LC₅₀ and LC₉₀ (21-fold) and the gradual slopes of dose–response curves indicated that the field population of this mosquito strain was heterogenous in response to deltamethrin. All four mosquito strains showed elevated levels of resistance to chlorpyrifos, with resistance ratios from 10 to 33. Nevertheless, except for the relatively low resistance to deltamethrin and chlorpyrifos, all mosquito strains showed a similar susceptibility or lower tolerance to the remaining insecticides tested compared with the susceptible Ikaken strain, even though some, such as permethrin, resmethrin, malathion, and Bti, have been used in the field for a long time, especially in Alabama. These results indicate that the development of resistance to insecticides in Ae. albopictus is slow and conventional insecticides, such as permethrin, resmethrin, malathion, and Bti, and relatively new insecticides, such as fipronil, imidacloprid, and spinosad, may all be valuable for the management of this important mosquito.

Exposure and sensitization to cockroach allergens is an importantrisk factor for allergic disease in humans. Despite a recent burgeoningof clinical and socioeconomic studies regarding environmentalpervasiveness and human exposure to cockroach allergens, little isknown about the basic biology of these proteins. The purpose of thisstudy was to ascertain gene expression patterns and the tissuedistribution of Blattella germanica allergen 1 (Bla g1), a perennial indoor environmental allergen, thought to be involvedin digestion in cockroaches. We also investigated the relativepotential contribution of different life stages of the German cockroachto environmental Bla g 1. Enzyme-linked immunosorbent assay was used toquantify the Bla g 1 contents of feces and various anatomical tissues,and Northern blot analysis was used to elucidate tissue-specificexpression of Bla g 1. Results showed that the Bla g 1 protein is mostprevalent in the midgut, and the Bla g 1 gene is exclusively expressedby midgut cells. Although Bla g 1 is produced by both sexes and alllife stages of the German cockroach, adult females produce and excretesignificantly more Bla g 1 in their feces than males or nymphs, evenwhen corrected for body mass or mass of voided feces. Our results showthat the concentration of Bla g 1 in feces of adult females is 6- to 7-and 30-fold higher than in adult males and nymphs, respectively,probably because females process more food than other life stages ofthe German cockroach.

In Brazil, dengue viruses (DENV) are transmitted by Aedes aegypti (L.). However, the recent introduction of Aedes albopictus (Skuse) has caused concern, because some populations of this species also are capable of DENV transmission. Ae. albopictus from rural and urban localities of São Paulo State, Brazil, were artificially exposed to infection with DENV-1 and -2 to evaluate their susceptibility. The rates of infection (6.2 and 5.7% for DENV-1; 5.3 and 12% for DENV-2) and dissemination (22.2 and 40% for DENV-1; 0 and 20% for DENV-2) were low in both urban and rural populations, with no significant differences detected between these mosquito populations.

Nestling mourning doves and house finches produced elevated viremias after inoculation with 2–3 log₁₀ plaque-forming units (PFU) of St Louis encephalitis (SLE) virus and infected 67 and 70% of Culex tarsalis Coquillett that engorged upon them, respectively. Mosquito infection rates as well as the quantity of virus produced after extrinsic incubation increased as a function of the quantity of virus ingested and peaked during days 3–5 postinoculation in mourning doves and days 2–4 in house finches. Only female Cx. tarsalis with body titers ≥4.6 log₁₀ PFU were capable of transmitting virus. Overall, 38% of females infected by feeding on mourning doves and 22% feeding on house finches were capable of transmission. The quantity of virus expectorated was variable, ranging from 0.8 to 3.4 log₁₀ PFU and was greatest during periods when avian viremias were elevated. Our data indicated that nestling mourning doves and house finches were competent hosts for SLE virus and that the quantity of virus ingested from a viremic avian host varies during the course of the infection and determines transmission rates by the mosquito vector.

Selected species of mosquitoes and Ornithodoros ticks were evaluated for their potential to transmit Karshi and Langat (tick-borne encephalitis virus complex) viruses in the laboratory. Although there was no evidence of replication of Karshi virus in either of the two mosquito species tested [Ochlerotatus taeniorhynchus (Wiedemann) or Culex pipiens (L.)], Karshi virus replicated in and was transmitted by all three species of Ornithodoros ticks tested (Ornithodoros parkeri Cooley, Ornithodoros sonrai Sautet & Witkowski, and Ornithodoros tartakovskyi Olenev). When inoculated with Karshi virus, 90% of Ornithodoros ticks (44/49) transmitted this virus by bite to suckling mice, and transmission continued to occur for at least 1 yr, the longest extrinsic incubation tested. After feeding on a suckling mouse with a viremia of ≈10⁵ suckling mouse subcutaneous lethal dose₅₀ units of Karshi virus per milliliter of blood, all three species of Ornithodoros tested became infected with and transmitted Karshi virus both trans-stadially and horizontally by bite to suckling mice. In addition, female O. tartakovskyi transmitted Karshi virus vertically to their progeny. In a continuation of a previous study, O. sonrai, orally exposed to Langat virus, were able to transmit this virus after >3 yr, the longest interval tested. Therefore, Ornithodoros spp. should be considered as potential vectors and as possible long-term maintenance hosts for Karshi virus and other members of the tick-borne encephalitis virus complex.

House finches, Carpodacus mexicanus, were experimentally infected with high and standard doses of western equine encephalomyelitis virus (WEEV) or St. Louis encephalitis virus (SLEV) to determine whether high doses would produce an elevated viremia response and a high frequency of chronic infections. Finches inoculated with ≈100,000 plaque forming units (PFU) of WEEV or SLEV produced viremia and antibody responses similar to those in finches inoculated with ≈100 PFU of WEEV or 1000 PFU of SLEV, the approximate quantities of virus expectorated by blood-feeding Culex tarsalis Coquillett. Infected finches were held through winter and then necropsied. Only one finch inoculated with the high dose of SLEV developed a chronic infection. Our data indicated that elevated infectious doses of virus may not increase the viremia level or the frequency of chronic infection in house finches.

The life table attributes of Culex tarsalis Coquillett females infected experimentally by feeding on 4 and 6 log₁₀ plaque-forming units (PFU) of western equine encephalomyelitis virus (WEEV) per milliliter of heparinized chicken blood were compared with an uninfected control group. Females continually were offered 10% sucrose and an oviposition substrate and daily a blood meal through a biomembrane feeder. Mortality (dead females) and fecundity (female eggs per female) were monitored daily until all females died. Overall, 94% of 198 females in the two virus-infected groups were positive for WEEV at death when tested by plaque assay; the average body virus titer at death did not differ between groups. WEEV infection significantly altered the life table characteristics of Cx. tarsalis. Life expectancy at infection in days (e_x), reproductive effort in female eggs per female per generation (R_o), and generation time (T) in days for the infected cohorts were significantly lower than for the uninfected controls, whereas the reproductive rate (r_c) in female eggs per female per day was higher for infected than uninfected cohorts. In agreement with the WEEV infection data that showed similar body titers, there were few differences between the life table parameters for the 4 and 6 log₁₀ PFU treatment groups. Greatest differences were observed for survivorship between days 17–40 when virus titers in infected dying females were greatest. Our data extend recent studies that indicate mosquito infection with encephalitis viruses has a cost of reduced life expectancy and fitness.

To test the hypothesis that adaptation to epizootic mosquito vectors mediates emergence of Venezuelan equine encephalitis virus (VEEV) from enzootic progenitors, experimental infection studies were conducted to determine the susceptibility of Ochlerotatus taeniorhynchus (Wiedemann) to epizootic and enzootic strains. Artificial blood meals containing epizootic subtype IC strains isolated during the 1962–1964, 1992–1993, and 1995 Venezuelan/Colombian epizootics and closely related Venezuelan enzootic subtype ID strains were used to compare infectivity and transmission potential. Their greater infectivity and replication suggested that adaptation of epizootic strains to Oc. taeniorhynchus may have enhanced epizootic transmission during the 1962–1964 and 1995 IC coastal epizootics. However, strains from the small 1992–1993 Venezuelan outbreak that did not extend to coastal regions do not seem to infect this species better than closely related subtype ID strains. Adaptation of VEEV to epizootic vectors such as Oc. taeniorhynchus mosquitoes may be a determinant of some but not all VEE emergence events and may influence spread into coastal regions.

An unusually high occurrence of Culex tritaeniorhynchus Giles resting indoors during daytime was observed in a Japanese encephalitis (JE) endemic area, Bellary district, Karnataka, India. Cx. tritaeniorhynchus, the primary vector of JE in this area, was the dominant species collected, and its abundance showed two peaks corresponding to rice crops in the district. More specimens (n = 20,966) were found resting in indoor habitats than in outdoor vegetation (n = 383), despite the availability of outdoor resting sites. This resting behavior is opposite to the Cx. tritaeniorhynchus behavior reported in the majority of JE-affected areas, where this species was captured in small numbers from indoor resting sites. Increased endophilic resting behavior indicates that indoor residual insecticides may provide an effective control method in this area.

Collections of Anopheles albitarsis Arribalzaga s.l. were conducted from May 1996 to June 2000 to estimate the human biting rate, and mark–release–recapture experiments were carried out to estimate the daily survival probability. The density of An. albitarsis females showed a marked seasonal variation, with peaks as high as 629 individuals per human per night in the wet season. The low daily survival probability of 0.61 is an important factor limiting the vectorial capacity of An. albitarsis s.l. in southeastern Brazil.