Despite tremendous efforts by public health organizations in dengue-endemic countries, it has proven difficult to achieve effective and sustainable control of the primary dengue virus vector Aedes aegypti (L.) and to effectively disrupt dengue outbreaks. This problem has multiple root causes, including uncontrolled urbanization, increased global spread of dengue viruses, and vector and dengue control programs not being provided adequate resources. In this forum article, we give an overview of the basic elements of a vector and dengue control program and describe a continuous improvement cyclical model to systematically and incrementally improve control program performance by regular efforts to identify ineffective methods and inferior technology, and then replacing them with better performing alternatives. The first step includes assessments of the overall resource allocation among vector/dengue control program activities, the efficacy of currently used vector control methods, and the appropriateness of technology used to support the program. We expect this will reveal that 1) some currently used vector control methods are not effective, 2) resource allocations often are skewed toward reactive vector control measures, and 3) proactive approaches commonly are underfunded and therefore poorly executed. Next steps are to conceptualize desired changes to vector control methods or technologies used and then to operationally determine in pilot studies whether these changes are likely to improve control program performance. This should be followed by a shift in resource allocation to replace ineffective methods and inferior technology with more effective and operationally tested alternatives. The cyclical and self-improving nature of the continuous improvement model will produce locally appropriate management strategies that continually are adapted to counter changes in vector population or dengue virus transmission dynamics. We discuss promising proactive vector control approaches and the continued need for the vector and dengue control community to incorporate emerging technologies and to partner with academia, business and the community-at-large to identify new solutions that reduce dengue.

We report the development of a new mosquito aspirator with the same aspiration capacity (airflow) of the CDC Backpack Aspirator (CDC-BP), but smaller and lighter (0.8 kg without battery), less expensive (US$45–70), easier to build, and compatible with the use of telescoping extension poles to access hard-to-reach locations. The performance of this new aspirator, named “Prokopack,” was compared with the CDC-BP in laboratory settings as well as in paired collections in combined sewer overflow (CSO) tunnels in Atlanta, GA, and indoor mosquito collections in Iquitos, Peru. The difference in suction power between both aspirators (average, 0.29–0.43 m/s) was negligible. However, 2.3 times more mosquitoes were collected using the Prokopack in the upper wall (>1.5 m) and ceilings of CSO tunnels than with the CDC-BP in lower walls. Indoor collection in Iquitos yielded significantly more total mosquito numbers [including Culex pipiens complex, Culex (melanoconion) sp., and Mansonia sp.] and Aedes aegypti (L.) in the Prokopack than in the CDC-BP. Our results demonstrate the effectiveness of the Prokopack to collect different mosquito species in different epidemiological settings.

Among several unusual species collected during surveillance of ectoparasites on wildlife hosts in the southeastern United States and Caribbean Region, the larvae of a new species of Whartonacarus were encountered in 2003 on a cattle egret, Bubulcus ibis (L.), in the Florida Keys. This is the first record for a member of Whartonacarus in the continental United States. The mite is described and named as Whartonacarus floridensis Mertins, and the possible significance of this discovery with respect to the “tropical bont tick,” Amblyomma variegatum (F.), is discussed. A brief taxonomic review of Whartonacarus raises questions about the putative synonymy of Whartonacarus nativitatis (Hoffmann) and Whartonacarus thompsoni (Brennan) and suggests that Whartonacarus shiraii (Sasa et al.) may include two distinct taxa. Whartonacarus is redefined, and a revised key to the known taxa is provided. Toritrombicula oceanica Brennan & Amerson is placed in the genus Whartonacarus. Also, Whartonacarus palenquensis (Hoffman) is rejected as a member of this genus and placed in its own new genus, Longisetacarus Mertins.

As a main vector of West Nile (WN) virus (family Flaviviridae, genus Flavivirus) in Europe, Culex modestus Ficalbi (Diptera: Culicidae) is commonly found in delta regions, lakes, and ponds. The Dombes area is located along one of the main corridors of bird migrations in France and lies 300 km north of the Camargue region, a frequent focus of WN virus circulation. It is an important breeding, wintering, and stopover site for many bird species that are putative carriers of viruses of different kinds. It is also a continental wetland with ≈1,200 fish farming ponds, scattered over the area, that provide suitable breeding sites for Cx. modestus. This article reports an entomological study based on larval surveys conducted in ponds in 2007 to assess the prevalence and abundance of Cx. modestus in the Dombes. Using the larval survey as an ecological screening test, we investigated the proportion of ponds found positive for Cx. modestus, and the relative abundance of this species was estimated in larval samples. We found that its pond distribution was more extensive in the 2007 survey than in that conducted in the 1970s. Survey methods and meteorological and anthropological factors that could account for the differences or variations between the findings of the two investigations are discussed.

The arrival and establishment of Aedes (Finhya) japnicus japonicus (Theobald) (Diptera: Culicidae) in Iowa are reported. In total, 518 wild adult specimens were collected through the statewide mosquito and mosquito-borne virus surveillance program in 2007 and 2008. Specimens were collected with New Jersey light traps, CO₂-baited CDC light traps, grass infusion-baited gravid traps, and Mosquito Magnet traps located in 12 counties in central and eastern Iowa. Specimens were identified morphologically, and identity was further supported by molecular DNA barcoding. Specimens also were tested for infection with West Nile virus (family Flaviviridae, genus Flavivirus, WNV) and La Crosse virus (family Bunyaviridae, genus Bunyavirus, LACV) by reverse transcription-polymerase chain reaction. Although no specimens tested positive for arbovirus infection, the arrival of Ae. j. japonicus in Iowa is a public health concern considering its potential to transmit several arboviruses, particularly WNV and LACV.

We examined the relationship between distance from major larval habitats and abundance of adult mosquitoes in the semiarid plains landscape characteristic of eastern Colorado. Mosquito collection was conducted from late June to early August 2007 and included trap locations at distances ranging from <10 m up to 20–150 m and 160–373 m from three major larval habitats: one area along a river corridor and two small reservoirs. The study yielded 65,140 mosquitoes of 14 species, and five species were sufficiently abundant to be included in statistical analyses: Aedes vexans (Meigen), Culex tarsalis Coquillett, Ochlerotatus dorsalis (Meigen) (=Ae. dorsalis), Ochlerotatus melanimon (Dyar) (=Ae. melanimon), and Culex pipiens L. Distance to nearest major larval habitat was not strongly related to Culex abundance within the ≈ 400-m range from larval habitats examined in this study. Abundance of Ae. vexans declined significantly with distance from the larval habitat, whereas abundance was significantly higher in the 20–150- and 160–373-m classes compared with areas within 10 m of the larval habitat for both Ochlerotatus species. Except for Ae. vexans, however, we did not find monotonic increasing or decreasing abundance trends associated with distance from larval habitats for the 400-m range examined. This, combined with a finding that fine-scale habitat heterogeneity influenced abundance for most of the mosquitoes examined, underscores the importance of considering not only distance from larval habitat but also fine-scale habitat heterogeneity to understand how important nuisance-biters and West Nile virus (family Flaviviridae, genus Flavivirus, WNV) vectors use the landscape. We also discuss how these results relate to previous studies from western North America and explore their relevance to operational implementation of adulticides to suppress mosquito vectors during WNV disease outbreaks in the Great Plains.

Female engorgement weight, oviposition, and molting times of larvae and nymphs of Amblyomma maculatum Koch (Acari: Ixodidae) were studied at various photoperiods under constant humidity and temperature in the laboratory. Ticks were held at photoperiods of 0:24, 10:14, 12:12, or 14:10 (L:D) h from egg through unfed nymphal stage and then at either the same or a different regime from fed nymphs to adults. No significant effects were observed on oviposition, female engorgement weights, survival, or molting time to unfed nymphs. Nymphal molting times were significantly shorter at the short-day regime (10:14) during the larval stage and 12:12 during the nymphal stage compared with those held at either 14:10 during both life periods or at 0:24 during both life periods. Longer molting times also were observed in ticks held at 12:12 during the larval phase and either 10:14, 12:12, or 0:24 during the nymphal phase compared with 14:10 during both life periods or 0:24 during both life periods. Ticks held at 10:14 during the larval phase and at 0:24 or 10:14 had longer molting times compared with those at 14:10 or 0:24 during both life periods. No differences in survival to either nymphal or adult stages were observed at any regime, and at day 25 no individuals were observed to be in developmental diapause. This study demonstrates that developmental diapause does not seem to be photoperiodically induced in fed nymphal A. maculatum in the laboratory.

Larval behavioral diapause was shown to be the major factor controlling the 1-yr generation pattern of Amblyomma cajennense (F.) (Acari: Ixodidae) in Brazil. During fieldwork, this behavior was shown to coincide with long daylength (>12 h) and high mean ground temperature (≈25°C), which prevail during spring-summer in Brazil. The current study evaluated biological parameters of engorged females, their eggs, and the resultant larvae inside plastic pots planted with the grass Brachiaria decumbens Stapf. held in incubators set with different combinations of temperature and photoperiod. Both the long daylength (photoperiod 14:10 [L:D] h) and high temperature (25°C) during larval hatching induced larval behavioral diapause, characterized by the confinement of hatched larvae on the ground below the vegetation for many weeks. When long daylength was present during hatching, but temperature was low (15°C), larvae did not enter diapause. Similarly, when short daylength (10:14 or 12:12) was present during larval hatching, larvae did not enter diapause regardless whether temperature was high (25°C). Termination of diapause was induced by shifting photoperiod from 14:10 to 12:12 or the temperature from 25 to 15°C. When applied to field conditions, the present results indicate that both high ground mean temperature (≈25°C) and long daylength (>12 h) during spring-summer (October—March) are responsible for the induction and maintenance of A. cajennense larval behavioral diapause in the field. Furthermore, both the low ground mean temperature (≈20°C) and the short daylength (<12 h) during autumn (April—May) are responsible for termination of larval behavioral diapause in the field.

In this study, we examined the stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), larval developmental habitat within the round hay bale feeding sites on cattle pastures, and we identified three zones with distinct characteristics around two types of hay feeders (ring and cone). The parameters monitored in each zone included stable fly emergence, substrate temperature, moisture, pH, thickness of hay-manure layer, and concentration of fecal coliform bacteria (Escherichia coli and Klebsiella oxytoca) as indicators of fecal material. All measurements were conducted during the period of high stable fly prevalence (HSF) in May-June and low stable fly prevalence (LSF) in July-August to better understand the environmental factors influencing stable fly seasonality. Substrate temperature and fecal coliform concentration were the only two significantly different factors between HSF and LSF. Temperatures ranged from 21 to 25°C during HSF versus 25–30°C in LSF but all were within the range for successful stable fly development. Fecal coliform concentrations ranged from 4.2 × 10³ to 4.1 × 10⁴ colony-forming units (CFU)/g of the substrate during HSF and from undetectable (<10) to 100 CFU/g during LSF. Furthermore, we evaluated the effect of different hay:manure ratios (0:1, 1:1, 2:1, and 5:1) on stable fly development (egg to adult). Temperature was significantly higher and stable fly developmental time significantly shorter in all substrates containing hay when compared with that of manure alone, but no significant differences were detected in stable fly emergence among the substrates. These results strongly indicate that the fecal microbial community plays an important role in stable fly larval development in hay feeding sites and that it is the main factor behind stable fly developmental seasonality on pastures. Our results also demonstrate that animal manure mixed with hay provides conditions for faster stable fly development than manure alone; however, hay does not significantly affect overall stable fly emergence.

In Chile, the horn fly, Hematobia irritans (L., 1758), is a major pest of grazing cattle and affects livestock production during the summer. Previous studies in Europe and the United States have shown that cattle flies, including H. irritans, are differentially attracted to individual cattle within herds and that volatile semiochemicals are responsible for this phenomenon. This study provides evidence that similar differential attractiveness occurs for the interaction between Chilean Holstein-Friesian cattle herds and local H. irritans populations. Thus, Holstein-Friesian dairy cattle, Bos taurus, which were of similar age and physiological condition, were shown to possess an uneven distribution of H. irritans. Heifers h6904 and h8104 were defined as low-carrier heifers and h5804, h2304 and h1404 as high-carrier heifers. Gas chromatography (GC) and coupled GC-mass spectrometric (GC-MS) analysis of samples collected from heifers revealed the presence of compounds previously reported as semiochemicals for cattle flies, including meta- and para-cresol, methylketones (C8–C11), and 6-methyl-5-hepten-2-one. Other compounds identified included carboxylic acids (butanoic, 3-methylbutanoic, pentanoic, and hexanoic acids), 1-hexanol, and 3-octanone. In Y-tube olfactometer studies, both m- and p-cresol attracted H. irritans at the highest doses tested (10-6 g), as did the positive control l-octen-3-ol. Of the other compounds tested, only 2-decanone and 2-undecanone produced a behavioral response, with significantly more flies being recorded in the control arm when the former compound was tested (at 10^-6 and 10^-8 g), and more flies being recorded in the treated arm for the latter compound (at 10^-7 g). This demonstration of behavioral activity with the identified compounds represents a first step for research into the application of semiochemicals in monitoring and control of cattle flies in Chile.

Our research tests the hypothesis that the inability to sugar-feed reduces the insemination rate in mosquito populations. To test this, we measured the effects of sugar availability on cumulative insemination performance of male Anopheles gambiae Giles s. s. (Diptera: Culicidae) during 10-d periods of continual emergence of equal numbers of both sexes, and we evaluated the implications at the population level with a matrix population model. On each day of each of four replicates, 20 newly emerged mosquitoes of each sex were recruited into the populations within two mesocosms, large walk-in enclosures with simulated natural conditions. Each mesocosm contained a cage to replicate the experiment on a small scale. Scented sucrose was absent or present (control). A human host was available nightly as a bloodmeal source in both mesocosms. Sugar availability and enclosure size significantly influenced female insemination. In the mesocosms, with sugar 49.7% of the females were inseminated, compared with 10.9% of the females without sugar. In the small cages, the insemination rates were 76.0 and 23.5%, respectively. In the mesocosms, cumulative survival of females after 10 d was 51.6% with sugar and 25.6% without sugar. In the cages, female survival was 95 and 73%, respectively. Sensitivity analysis of the population projection matrix shows that both reduced male survival and reduced mating capability due to a lack of sugar contributed to lower insemination rates in females, and in the absence of sugar the insemination rate was lowered to an extent that led to population decline.

Species-specific differences in the responses of egg-laying mosquitoes (Diptera: Culicidae) to the presence of fish exudates in oviposition sites in laboratory bioassays have been related to the likelihood of encountering mosquito-eating fish in natural oviposition sites. We examined the responses of egg-laying mosquitoes to the presence of larvivorous fish in oviposition sites to test this hypothesis in the field. The number of Culex tarsalis Coquillett egg rafts laid on mesocosms (15.5 m²; 8 m³) containing caged mosquitofish (0.066 Gambusia affnis per liter) was reduced by 84% relative to mesocosms lacking fish. Egg-laying Culex quinquefasciatus Say did not differentiate significantly between comparatively small (0.11 m²) oviposition sites containing water conditioned with mosquitofish (0.3 G. affnis per liter) versus aged reservoir water. Cx. quinquefasciatus egg rafts were not collected from the larger mesocosms, and Cx. tarsalis egg rafts were rarely collected from the smaller oviposition sites. Oviposition preferences for characteristics of aquatic habitats that lack fish (e.g., small size, semipermanence, and high levels of organic enrichment in which hypoxic conditions are prevalent) may limit the coexistence of immature stages of some mosquito species such as Cx. quinquefasciatus and insectivorous fish. Mosquito species such as Cx. tarsalis that also use comparatively large water bodies as developmental sites may have evolved the ability to detect the presence of predatory fish.

Aedes aegypti L. (Diptera, Culicidae) is the main vector of dengue and yellow fever. In Argentina, the species was apparently eradicated approximately in 1964; by 1986, it was reintroduced. To identify different gene pools in geographical populations of the species and to ascertain the possible routes of colonization, we analyzed the diversity of mitochondrial DNA haplotypes in 572 specimens from Argentina and neighboring countries. We found that the restriction fragment length polymorphism-polymerase chain reaction screening of a large DNA fragment including the A T-rich region was the best strategy to reconstruct the colonization pattern of Ae. aegypti in Argentina. Twenty haplotypes were recognized; levels of genetic similarity varied among populations from different geographical locations. The haplotype network constructed on the basis of genetic distances showed three well differentiated groups. Two of them exhibited a well defined spatial distribution and populations in these groups presented an isolation-by-distance pattern. The persistence of relictual populations after the last eradication campaigns would explain the high levels of haplotype diversity and the presence of exclusive haplotypes in urban centers from northwestern Argentina. Eastern Argentine populations showed one prevalent haplotype, also predominant in Brazil and Paraguay. Our results highlight the need for efficient surveys and control campaigns, given the strong effect of land trade on genetic exchange among mosquito populations from Argentina and neighboring countries where dengue is endemic.

Mutations I48L, I54V, R86Q, V137I, I492M, and T548A were identified previously in BmAChE3, a gene encoding acetylcholinesterase, from the organophosphate (OP) acaricide-resistant San Román strain of Rhipicephalus (Boophilus) microplus. Recombinant BmAChE3 acetylcholinesterase containing the R86Q mutation was shown to exhibit nearly 20-fold reduction in the rate of phosphorylation by paraoxon relative to the wild-type sequence. In addition, the R86Q mutation was present in resistant laboratory strains at elevated frequency compared with OP-susceptible strains but was insufficient to alone generate the OP-resistant phenotype (J. Med. Entomol. 44:1013–1018). Here, we developed assays to genotype the remaining five mutations and evaluated frequency of all six BmAChE3 mutations in individual R. microplus ticks from laboratory and Mexican field-collected strains. We found a substantial number of individuals in known OP-susceptible strains that seemed to be homozygous for each of the mutations surveyed, the exception being I48L, which was infrequent in all strains, leading us to conclude that none of the mutations alone were responsible for generation of phenotypic resistance to OP acaricide.

Cytochrome b, coded by mitochondrial DNA, is one of the cytochromes involved in electron transport in the respiratory chain of mitochondria. Cytochrome b is a critical intermediate in a mitochondrial death pathway. To reveal whether cytochrome b of the mosquito Aedes aegypti (L.) (Diptera: Culicidae) (AeaCytB) is developmentally regulated, we used real-time quantitative polymerase chain reaction (qPCR) to examine AeaCytB gene expression levels in different developmental stages of Ae. aegypti. The qPCR showed that AeaCytB was expressed in each developmental stage, with peaks at first and second instars and was highly expressed in teneral male and female Ae. aegypti adults. Because mitochondrial genes exist as multiple copies, AeaCytB has much higher expression levels in all developmental stages in Ae. aegypti compared with nuclear genes. We also investigated the effect of abiotic environmental factors (e.g., high temperatures, ultraviolet radiation, and pesticide) on AeaCytB gene expression. Taken together, these results suggest that AeaCytB gene plays an important role in the development of Ae. aegypti and its response to environmental stress.

Mosquitoes play an important role as vectors for a variety of pathogens. Insecticide use for control means results in selection of tolerant/resistant mosquitoes. An esterase cDNA was isolated from Culex nigripalpus Theobald (Diptera: Culicidae), and its spatial expression was characterized. GenBank tblastx and VectorBase searches with the translation product of the longest cDNA fragment (397 bp, CN Temsha est-1) of the Cx. nigripalpus esterase revealed similarity (95%) to the estalpha2 esterase gene product of Culex pipiens quinquefasciatus Say, suggesting it is a member of the esterase family. Transcripts encoding Cx. nigripalpus esterase were detected in midgut tissue, thoraces, and abdomens of female Cx. nigripalpus, findings that may support possible roles in feeding, digestion, or reproduction. Gene expression studies to determine the role of Cx. nigripalpus esterase in the mosquito are being conducted.

We previously showed that gene expression in the midgut of female Culex nigripalpus Theobald (Diptera: Culicidae) was altered after ingestion of a bloodmeal and some of the expressed cDNAs showed stage-, sex-, and tissue-specific expression. One of these expressed cDNAs, CN G11B, is here shown to be similar to members of a gene family that encodes odorant-binding proteins. CN G11B.1 is a cDNA fragment of 721 bp, is incomplete at the 5′-end, and contains a canonical polyadenylic acid tail signal sequence in the 103-bp 3′-untranslated region. Translation of CN G11B.1 provides a putative protein product of 207 amino acids. GenBank tblastx, VectorBase, and Pfam database searches showed identity to hypothetical proteins from Culex pipiens quinquefasciatus Say (86%) and Aedes aegypti (L.) (55%). These proteins have structural motifs similar to those found in the gene family that includes odorant-binding proteins. CN G11B.1 putative protein has two of the six cysteines that are highly conserved in most invertebrate odorant-binding proteins. CN G11B.1 expression increased in thoraces (6–12 h) and in abdomens (3–48 h) of blood fed female Cx. nigripalpus but was not detected in RNA from heads, indicating a possible role in both chemoreception and blood feeding.

Using a proteomics approach, we identified 13 differentially abundant proteins in heads of nondiapause, early, and mid-diapause Culex pipiens L. adult females. Three proteins that were more abundant during early diapause showed highest identities to pupal cuticle protein (PCP). The majority of less abundant proteins were involved in energy metabolism and cytoskeletonal reorganization. The increase of PCP in early diapause may be involved in enhancing stress resistance in the cuticle, a response akin to the general enhancement of stress resistance associated with overwintering insects. PCP also may have utility as a biomarker for early diapause in this species.

Kunzea ambigua (Smith) Druce (Myrtaceae) is an Australian native plant, commonly known as tick bush. The essential oil of the plant has been proposed as a potential mosquito repellent. Commercial K. ambigua oil was analyzed by gas chromatography-mass spectrometry (GC-MS) and its composition compared with that of oils from two individual K. ambigua plants and citronella oil. K. ambigua oils were studied for their repellency against Aedes aegypti L. Formulations of three different K. ambigua essential oils (30% vol:vol) were tested for repellency to mosquitoes using human volunteers. One oil was compared with citronella and N,N′-diethyl-3-methylbenzamide (deet) for repellency. Oil formulations were also tested for repellency with and without the addition of 5% vanillin. The formulation containing commercially produced K. ambigua oil had a mean complete protection time (CPT) of 49 ± 24 (SD) min. All the K. ambigua formulations had comparable repellency to 40% citronella. However, the 60% citronella formulation showed higher repellency than the 40% K. ambigua formulation. The addition of 5% vanillin did not increase the repellency of K. ambigua oil. Both K. ambigua oil and citronella were significantly less repellent than deet. The K. ambigua essential oil formulations should not be advocated for use as repellents in regions prone to mosquito-borne disease.

Open marsh water management (OMWM) is a commonly used approach to manage salt marsh mosquitoes than can obviate the need for pesticide application and at the same time, partially restore natural functions of grid-ditched marshes. OMWM includes a variety of hydrologic manipulations, often tailored to the specific conditions on individual marshes, so the overall effectiveness of this approach is difficult to assess. Here, we report the results of controlled field trials to assess the effects of two approaches to OMWM on larval mosquito production at National Wildlife Refuges (NWR). A traditional OMWM approach, using pond construction and radial ditches was used at Edwin B. Forsythe NWR in New Jersey, and a ditch-plugging approach was used at Parker River NWR in Massachusetts. Mosquito larvae were sampled from randomly placed stations on paired treatment and control marshes at each refuge. The proportion of sampling stations that were wet declined after OMWM at the Forsythe site, but not at the Parker River site. The proportion of samples with larvae present and mean larval densities, declined significantly at the treatment sites on both refuges relative to the control marshes. Percentage of control for the 2 yr posttreatment, compared with the 2 yr pretreatment, was >90% at both treatment sites.

Vapor toxicities of two prototype formate esters, ethylene glycol di-formate (EGDF) and heptyl formate, and the prototype heterobicyclic menthofuran were determined against laboratory-reared adult house flies, Musca domestica L. (Diptera: Muscidae). Toxicities were compared between house flies and other dipteran species tested previously. The organophosphate fumigant insecticide dichlorvos (DDVP) was used as a positive control. Although less toxic than DDVP, all three prototype compounds were toxic to house flies. Most toxic was menthofuran (LC₅₀ = 3.70 mg/liter air), followed by EGDF (LC₅₀ = 9.27 mg/liter air) and heptyl formate (LC₅₀ = 32.62 mg/liter air). The toxicity of menthofuran when applied after piperonyl butoxide increased 1.5-fold. The toxicities of heptyl formate and EGDF when applied after S,S,S-tributyl phosphorotrithioate decreased by 1.5-and 2-folds, respectively. These results are slightly different from results obtained for other dipterans, further supporting previous hypotheses that toxicity may have some species specificity. Ceramic porous rods impregnated with heptyl formate were used to evaluate the effectiveness of controlled vapor release for a single dose of heptyl formate against house flies. Controlled vapor release of heptyl formate can be used successfully to provide prolonged house fly mortality. Even though the prototype compounds did not exhibit toxicity as high as that of DDVP, their toxicities to dipterans, along with their reduced mammalian toxicities relative to DDVP, make them potential DDVP replacement candidates.

This study quantified both contact irritancy and noncontact repellency behavioral responses of three strains of Aedes aegypti (L.) (one long-term colony and two F1–F2 generation field-caught strains) to field application rates of DDT (2g/m²) and α-Cypermethrin (ACyp) (0.025 g/m²) by using an excito-repellency test chamber. The colony The colony strain (USDA) was completely susceptible to DDT and ACyp. One field strain was collected from Chiang Mai (CM) Province, northern Thailand, and was characterized as tolerant (reduced susceptibility) to DDT and completely susceptible to ACyp. The second field strain, collected from Kanchanaburi (KAN) Province, western Thailand, was highly resistant to DDT but fully susceptible to ACyp. All three strains exhibited marked irritancy to contact with ACyp, with more pronounced escape responses occurring in the two field strains. With DDT, the KAN strain demonstrated the lowest escape response during both contact and noncontact trials, whereas a greater response was seen in trials conducted with CM and USDA strains. With exposure to ACyp, repellency was less profound than irritancy but still resulted in a significant escape response compared with paired controls without insecticide (P < 0.05). DDT elicited both irritancy and repellency responses but comparably greater spatial repellency than ACyp. Findings indicate ACyp functions primarily as a strong contact irritant, whereas DDT functions as a relatively strong noncontact repellent in the strains tested. The higher the degree of physiological resistance to DDT, the greater the apparent suppression of both behavioral avoidance responses. Most importantly, observations using susceptible, tolerant, and resistant Ae. aegypti strains show that behavioral responses that can interrupt human-vector contact still occur regardless of degree of physiological susceptibility to compounds tested.

Specimens of Salvadora persica Wallich (Salvadoraceae), Pistacia atlantica Desfontaines (Anacardiaceae), and Juniperus phoenicea L. (Cupressaceae) were collected at The Green Mountain in northeastern Libya. The tick-repellent effects of the essential oils from the plants were evaluated using host-seeking nymphs of Ixodes ricinus L. (Acari: Ixodidae) in the laboratory. Significant tick repellent effects were observed for the oils of all three species, but the duration of action was short. The oils were obtained by steam distillation. Volatile compounds of the essential oils were collected by solid phase microextraction and the constituents were identified by gas chromatographymass spectrometry.

The toxicity of several compounds isolated from Asarum heterotropoides root steam distillate to third-instar larvae of Culex pipiens pollens Coquillett, Aedes aegypti (L.), and Ochlerotatus togoi Theobald was examined using a direct contact mortality bioassay. Safrole was the most toxic constituent to Cx. p. pallens and Ae. aegypti larvae, whereas terpinolene was most toxic to Oc. togoi. However, LC⁵⁰ values of these three mosquito larvae to both essential oils as well as the remainder of the 26 compounds identified in A. heterotropoides were considerably greater than for fenthion or temephos. However, we suggest that constituents of A. heterotropoides root steam distillate merit further study as potential mosquito larvicides due to global efforts to reduce the level of highly toxic synthetic pesticides in the aquatic environment.

Insecticides are the most important component in the vector-control effort and pyrethroids such as permethrin are widely used for the indoor control of mosquitoes worldwide. However, the widespread development of resistance to pyrethroids is becoming a major problem. The current study reports an extensive survey of permethrin resistance in Alabama designed to characterize the importance of the L-to-F kdr mutation in pyrethroid resistant Culex mosquitoes. Mosquitoes were collected from 19 counties, 17 in Alabama and two from neighboring counties in Florida and Tennessee. Culex quinquefasciatus Say from all the counties tested were found to have developed resistance to permethrin. Seventy one percent of the field population from Alabama exhibited relatively low levels of resistance, with resistance ratios ranging from 71 to 390; 11% had medium/high levels of resistance, with resistance ratios ranging from 810 to 830; and the remaining 18% had high levels of resistance, with resistance ratios ranging from 1,100 to 1,400. Most of the mosquito populations tested showed a strong correlation between their level of resistance and the frequency of L-to-F mutation expression, suggesting the importance of target site insensitivity in the development of permethrin resistance. However, four populations with elevated levels of resistance showed no L-to-F mutation in their sodium channels. Although it is possible that other mutations other than L-to-F are present in the sodium channel, resulting in permethrin resistance in these four field populations, resistance mechanisms other than target site insensitivity also must be considered.

AeSCP-2 inhibitors (SCPIs) compete with cholesterol for binding to a mosquito sterol carrier protein-2 (AeSCP-2) known to aid in the uptake of cholesterol in mosquito cells. The larvicidal activities of AeSCP-2 inhibitor-1 (SCPI-1) and inhibitor-2 (SCPI-2) against Culex quinquefasciatus Say (Diptera: Culicidae) were therefore examined in insecticide-resistant Culex mosquitoes HAmCq^G9, MAmCq^G2, and BAmCq^G0. All of the resistant Culex mosquito strains exhibited similar sensitivity to SCPI-1 and SCPI-2 inhibitors compared with a susceptible S-Lab strain. When an AeSCP-2 inhibitor was applied simultaneously with permethrin, the toxicity of permethrin to the second-instar larvae of all four strains of Culex mosquitoes increased, suggesting a synergistic effect of AeSCP-2 inhibitors on the toxicity of permethrin against Culex mosquitoes. Both SCPI-1 and SCPI-2 inhibitors caused a 2.4-to 3-fold reduction in the level of permethrin resistance in the highly resistant strain HAmCq^G9. This result suggests that the mode of action of the AeSCP-2 inhibitors, which reduces the uptake of cholesterol by inhibiting the function of AeSCP-2 in mosquito cells, may interfere with the mechanisms or ability that govern permethrin resistance in the HAmCq^G9 mosquito strain.

Arcott sheep were evaluated as a model for studying active and passive immunity to tick paralysis caused by Dermacentor andersoni (Stiles). The incidence of tick paralysis in sheep increased from 0 at doses ≤0.33 ticks per kg to 100% at ≥0.8 ticks per kg. The dose required for 50% paralysis was 0.42 ticks per kg. Expressing dose as a ratio of initial ticks per unit body weight removed differences in response due to sheep weight. The interval from infestation to paralysis decreased from >12 d at 0.4 ticks per kg to <8 d at 1.3 ticks per kg. After exposure to a paralyzing doses of ticks, the incidence of paralysis varied among sheep that were naive (six of six, 100% paralysis), previously paralyzed (zero of six, 0% paralysis), and passively immunized with an intravenous treatment of 300 ml of serum from immune cattle (two of six, 33% paralysis). Sheep that were actively immunized by previous exposure had antibodies to a greater number of tick salivary antigens compared with those that were not immune. Antibodies to a 43.3-kDa antigen had 72% agreement with immunity to paralysis, and a sensitivity and specificity of 0.60 and 0.88, respectively. In conclusion, previously paralyzed sheep had developed antibodies against D. andersoni and were not susceptible to subsequent paralysis, whereas passive immunization conferred protection against paralysis in only some sheep.

Transovarial transmission of Orientia tsutsugamushi (Hayashi) in laboratory colonies of Leptotrombidium chiangraiensis Tanskul & Linthicum and Leptotrombidium imphalum (Vercammen-Grandjean & Langston) (Acari: Trombiculidae) was studied for two generations. In L. chiangraiensis, the transovarial and filial infection rate was 100% in each generation. Only infected females were produced. In L. imphalum, the transovarial infection rate of the parental generation was 100% but declined to 93.3% in the F₁ generation. The overall filial infection rate was 100% in the F₁ but was only 62.3% in the F₂ generation. In infected lines, only infected females were produced in the F₁ generation, but 1.5% of the F₂ progeny were infected males. Lower rates of transovarial transmission in L. imphalum may be the cause of the lower natural infection rates found in nature.

We report on the effect of tsetse fly starvation on the maturation of an established Trypanosoma brucei brucei midgut infection, i.e., the development of procyclic infection into the infectious metacyclic parasites in the tsetse fly salivary glands. Glossina morsitans morsitans flies were nutritionally stressed 10 d after the uptake of a T. b. brucei-infected bloodmeal by depriving these flies from feeding for seven consecutive days, whereas the control fly group (nonstarved group) continued to be fed three times a week. After this period, both fly groups were again fed three times per week on uninfected rabbit. Thirty days after the infected bloodmeal, all surviving flies were dissected and examined for the presence of an immature midgut and a mature salivary gland trypanosome infections. Results showed a significantly increased proportion of flies with salivary gland infection in the nutritionally stressed fly group suggesting an enhanced maturation of the trypanosome infection. These data suggest that environmental factors that cause nutritional stress in a tsetse population do not only make tsetse flies significantly more susceptible to establish a midgut infection as was shown previously but also boost the maturation of these midgut infections.

Although yellow fever (YF) has not been reported on the eastern coast of Brazil since 1942, there was a reemergence of dengue fever in Rrazil in 1987 due to the reintroduction of Aedes aegypti (L.). To assess areas of potential risk for transmission of vector-borne diseases, a surveillance system was placed in a large Atlantic Forest reserve in Natal, Rio Grande do Norte, Brazil, where in 2004 unexplained epizootics were reported among marmosets. The etiologic agent causing the mortality in marmosets has not been identified. Wyeomyia bourrouli Lutz, Haemagogus leucocelaenus Dyar & Shannon, Ae. aegypti, Aedes albopictus (Skuse), Ochlerotatus scapularis Rondani, Ochlerotatus serratus Theobald, Ochlerotatus taeniorhynchus Wiedemann, Culex quinquefasciatus Say, and Limatus durhami Theobald were collected in the park and in the proximity of the households adjacent to the park. Seasonal abundance fluctuation was significant for Ae. aegypti, Ae. albopictus, Ochlerotatus scapularis (Rondani), and Hg. leucocelaenus. Eggs of Ae. aegypti, Ae. albopictus, and Hg. leucocelaenus were more frequently found at the conclusion of the rainy season. A significant negative correlation between the number of Ae. albopictus collected and temperature was observed (r = -0.50), i.e., for each 1°C increase in temperature, the number of specimens collected decreased eight-fold. The findings reported herein reinforce the need for a sustainable arboviral surveillance program in this area to decrease the potential risk of emergence of vector borne diseases as YF.

Salp15 is a multifunctional protein, vital to the tick in its need to obtain vertebrate host blood without stimulating a host inflammatory and immune response. The Salp15 protein from both Ixodes scapularis Say and Ixodes ricinus (L.), the principal vectors of the Lyme disease spirochete in eastern North America and Europe, respectively, have been well characterized and found to bind the murine CD4 receptor, DC-SIGN, and the OspC protein of Borrelia burgdorferi. In the current study, we characterized the full salp15 gene in Ixodes pacificus Cooley & Kohls and Ixodes persulcatus Schulze, the principal vectors of Lyme disease spirochetes in western North America and Asia, respectively. In comparing the Salp15 protein of all four principal vector ticks of public health importance for the transmission of Lyme disease spirochetes, we find the 53 C-terminal amino acids to have a high degree of similarity. There are at least three clades in the tree of Salp15 and its homologues, probably representing a multigene family.

The establishment of the potential vector species Aedes (Finlaya) japonicus japonicus (Theobald) (Diptera: Culicidae) in southern Belgium is reported. The species was most likely introduced through the international trade in used tires. It was first collected in 2002 on the premises of a second-hand tire company and was sampled using different sampling methods in the two consecutive years (2003–2004). It was only in 2007 and 2008, during a national mosquito survey (MODIRISK), that its presence as adults and larvae at the above-mentioned site and at another tire company in the area was confirmed based on morphological and molecular identification. This discovery is the first record for Belgium of an exotic mosquito species that established successfully and raises the question on the need for monitoring and control. Considering the accompanying species found during the surveys, we also report here the first observation of Culex (Maillotia) hortensis hortensis (Ficalbi) in Belgium.

Rates of infection of Amblyomma americanum (L.) by Ehrlichia chaffeensis were compared in 100 ticks collected from sites in each of four states: Indiana, North Carolina, Kentucky, and Mississippi. The overall infection rates were similar among sites, ranging from 1 to 4%. Because pathogenic differences may exist between E. chaffeensis strains, nested polymerase chain reaction (PCR) amplification of the variable-length PCR target (VLPT), and sequencing of the amplicons were performed to differentiate between strains. The most common infecting strains at all sites exhibited a repeat profile of 1,2,3,4 (corresponding to the Arkansas/Jax/Osceola and Liberty strains). To determine whether the minimum infection rates (MIRs) or the most common infecting strain were changing over time in southern Indiana sites, 2,765 ticks from six counties in 2000 and 837 ticks from seven counties in 2004 also were examined in pools of five ticks per pool. The MIRs for 2000 and 2004 were 3.5 and 4.2% respectively, suggesting that the overall MIRs remained low. At two sites, in Pike and Harrison counties, however, infection rates more than doubled from 2000 to 2004 (7 to 16% and 0.3 to 2.7% respectively). Across all sites, the most common infecting strains (Arkansas/Jax/Osceola and Liberty) did not significantly change (68% in 2000; 79% in 2004).

The potential vectors of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in Doña Ana County, NM, were determined during 2004 and 2005. Trapping was conducted using Centers for Disease Control and Prevention miniature light-traps baited with dry ice, and gravid traps baited with a hay infusion. In addition, sentinel chickens were housed at four of the trapping locations to monitor WNV epizootic transmission. In total, 5,576 pools consisting of 115,797 female mosquitoes were tested for WNV by reverse transcription-polymerase chain reaction, of which 152 from 13 mosquito species representing six genera were positive. Culex tarsalis Coquillett, Culex quinquefasciatus Say, Culex erythrothorax Dyar, Aedes vexans (Meigan), and Psorophora columbiae (Dyar & Knab) accounted for 86% of all detections. Based on the frequency of WNV detection, our data indicate primary and secondary vector roles for Cx. tarsalis and Cx. quinquefasciatus, respectively, with Cx. erythrothorax, Ae. vexans, and Ps. columbiae as occasional vectors of WNV in Doña Ana County. Other species testing positive for the virus included Aedes aegypti (L.), Anopheles franciscanus McCracken, Culex stigmatosoma Dyar, Culiseta inornata (Williston), Ochlerotatus dorsalis (Meigan), Ochlerotatus sollicitans (Walker), Ochlerotatus trivittatus (Coquillett), and Psorophora signipennis (Coquillett). Although they occurred after initial WNV detections in mosquitoes, in total, 21 seroconversions in sentinel chickens were detected during the study.

Surveys in 2001, 2005, and 2006 attempted to determine the role of wildlife in maintenance and dissemination of the tropical bont tick, Amblyomma variegatum (F.) (Acari: Ixodidae), in St. Croix, U.S. Virgin Islands. Small mammals; birds; white-tailed deer, Odocoileus virginianus (Zimmermann); and feral cattle, Bos taurus L., were examined at nine premises, in mountainous rain forest, and in surrounding areas in western St. Croix, an area including and central to all known bont tick-infested premises on the island. Small Asian mongooses, Herpestes javanicus (É. Geoffroy Saint-Hilaire), yielded 1,566 ectoparasite specimens, representing five species, and including larvae of a soft tick, Carios puertoricensis (Fox); the tropical horse tick, Anocentor nitens (Neumann); and the southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini). Black rats, Rattus rattus L., yielded 144 specimens, representing six ectoparasite species, including C. puertoricensis. Of 25 bird species examined, seven yielded 116 ectoparasite specimens representing at least 14 different species of lice and mites, but no ticks. White-tailed deer and feral cattle yielded only various stages of A. nitens and R. microplus ticks. A. variegatum was not encountered on any potential wildlife host sampled, reflecting its low occurrence in St. Croix during the survey period. One collection of chewing lice (Phthiraptera: Philopteridae) from a spotted sandpiper, Actitis macularia (L.), and collections of feather mites (Acari: Astigmata: Trouessartiidae) from both bananaquits, Coereba flaveola (L.), and black-faced grassquits, Tiaris bicolor (L.), may represent new, undescribed species.

During the hunting season 2007–2008, 494 Dermacentor marginatus (Sulzer) ticks were collected from 109 hunter-killed wild boars, Sus scrofa, in Lucca's province, Tuscany, Italy. Rickettsia slovaca, the causative agent of tick-borne lymphadenopathy (TIBOLA), was detected in 32.1% of ticks tested (n = 112) by using polymerase chain reaction primers targeting gltA, ompA, and ompB rickettsial genes. Moreover, Rickettsia raoultii was found for the first time in Italy, with 1.8% infection prevalence. This study confirms the risk posed to humans by ticks and tick-borne pathogens in the study area, where cases of spotted fever rickettsiosis (TIBOLA) are reported.

The relative efficacy of gravid and under-house CO₂ traps for monitoring mosquito species of public health importance within the Houston metroplex area was assessed. Gravid and under-house traps were colocated at 10 sites and monitored weekly between 1 March to 31 May 2007. The most numerous species caught was Culex pipiens quinquefasciatus Say. Other species of public health importance caught in gravid and under-house traps included Culex restuans Theobald, Aedes aegypti (L.), and Aedes albopictus Skuse. Adjusting for the week of collection, gravid traps caught significantly more mosquitoes (mean 23.1 per trap) in the study area than under-house traps (mean 3.6 per trap). However, under-house traps caught a greater variety of mosquito species (13) than gravid traps (11). Gravid and under-house traps only caught nine of 15 of the same mosquito species during the study period. In this study area, gravid traps should be used as the primary method of surveillance for mosquito-borne diseases of public health importance during the early part of the season, because of greater catch numbers of mosquitoes that pose a public health risk.

Mosquito-borne arboviral epidemics tend to strike without warning. The driving force for these epidemics is a combination of biotic (vector, amplification host, and virus) and abiotic (meteorological conditions, especially rainfall and temperature) factors. Abiotic factors that facilitate the synchronization and interaction of vector and amplification host populations favor epidemic amplification and transmission. In Florida, epidemics of St. Louis encephalitis (SLE) virus (family Flaviviridae, genus Flavivirus, SLEV) have been preceded by major freezes one or two winters before the onset of human cases. Here, we analyze the relationship between severe winter freezes and epidemic SLEV transmission in peninsular Florida and show that there is a significant relationship between the transmission of SLEV and these severe freezes. We propose that by killing cold-sensitive understory vegetation in the mid-peninsular region of Florida, freezes enhance the reproductive success of ground-feeding avian amplification hosts, especially mourning doves and common grackles. In conjunction with other appropriate environmental signals, increased avian reproductive success may enhance SLEV and West Nile (WN) virus amplification and result in SLE and WN epidemics during years when all of the biological cycles are properly synchronized. The knowledge that winter freezes in Florida may enhance the amplification and epidemic transmission of SLE and WN viruses facilitates arboviral tracking and prediction of human risk of SLE and WN infection during the transmission season.

To ascertain mosquito species-specific oviposition height preferences, a study was conducted evaluating the response of field populations of container-inhabiting mosquitoes to water, oak (Quercus spp.), or oak—pine (Pinus spp.) infusion-baited ovitraps in four suburban and four sylvatic habitats in north central Florida. In total, 48 ovitraps, 24 suspended at each height of 1 or 6 m (near the ground or tree canopy, respectively), were monitored weekly for 5 mo. Throughout our study, we collected 13,276 mosquito eggs, representing five species from four genera, the most common being Aedes triseriatus (Say), Aedes albopictus Skuse, and Orthopodomyia signifiera (Coquillett). Significantly more Ae. triseriatus and Ae. albopictus eggs were oviposited in containers with oak and oak—pine infusions compared with water alone. Significantly more Ae. albopictus eggs were recovered from traps at 1 m in suburban habitats, whereas more Ae. triseriatus eggs were recovered at 6 m in sylvatic habitats.

Wistar rats (Rattus norvegicus) infested with Dermatobia hominis (L. Jr., 1781) had their axillary lymph nodes removed and histopathologically processed. Follicular hyperplasia in the germinal center was noted from 2 d postinfestation (dpi), exhibiting a high number of centerblasts, mitotic and apoptotic cells, and a thin parafollicular area. The paracortex showed hyperplasia rich in dendritic cells, immunoblasts, and endothelial venules, with diapedesis seen from 4 dpi onward. Hyperplasia of the medullar sinus also was first observed at this point, as well as dilated lymphatic sinus, lymph, macrophages, neutrophils, mast cells, and eosinophils. Medullar strings were expanded and filled with immunoblasts, mitotic cells, and plasmocytes. Lymphadenitis was not observed. The expression of mast cells was similar for both myiasis-affected and control rats but increased significantly (mastocytosis) at 7 and 15 d postlarval emergence (dple). Eosinophilia was observed at 4, 10, 15, 20, and 28 dpi as well as at 2, 7, and 15 dple, particularly on the last three observations of dpi and the earliest dple. This experimental approach allowed progressive tissue reactions in the lymph nodes to be monitored during myiasis, particularly those involving mast cells and eosinophils. These reactions abated and complete repair was observed at 60 dple.

We examined seasonal patterns for entomological measures of risk for exposure to Culex vectors and West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in relation to human WNV disease cases in a five-county area of northeastern Colorado during 2006–2007. Studies along habitat/ elevation gradients in 2006 showed that the seasonal activity period is shortened and peak numbers occur later in the summer for Culex tarsalis Coquillett females in foothills-montane areas > 1,600 m compared with plains areas <1,600 m in Colorado's Front Range. Studies in the plains of northeastern Colorado in 2007 showed that seasonal patterns of abundance for Cx. tarsalis and Culex pipiens L. females differed in that Cx. tarsalis reached peak abundance in early July (mean of 328.9 females per trap night for 18 plains sites), whereas the peak for Cx. pipiens did not occur until late August (mean of 16.4 females per trap night). During June-September in 2007, which was a year of intense WNV activity in Colorado with 578 reported WNV disease cases, we recorded WNV-infected Cx. tarsalis females from 16 of 18 sites in the plains. WNV infection rates in Cx. tarsalis females increased gradually from late June to peak in mid-August (overall maximum likelihood estimate for WNV infection rate of 8.29 per 1,000 females for the plains sites in mid-August). No WNV-infected Culex mosquitoes were recorded from sites > 1,600 m. The vector index for abundance of WNV-infected Cx. tarsalis females for the plains sites combined exceeded 0.50 from mid-July to mid-August, with at least one site exceeding 1.00 from early July to late August. Finally, we found that abundance of Cx. tarsalis females and the vector index for infected females were strongly associated with weekly numbers of WNV disease cases with onset 4–7 wk later (female abundance) or 1–2 wk later (vector index).

The microbial flora associated with fleas may affect their ability to transmit specific pathogens, including Yersinia pestis, and also could be used to develop paratransgenesis-based approaches to interfere with transmission. To begin addressing this hypothesis, the microbial flora associated with the relatively efficient Y. pestis vectors Xenopsylla cheopis (Rothschild) (Siphonaptera: Pulicidae) and Oropsylla montana (Baker) (Siphonaptera: Ceratophyllidae), and the inefficient vector Ctenocephalides felis felis (Bouché) (Siphonaptera: Pulicidae) were investigated using polymerase chain reaction amplification of 16S rDNA genes. DNA sequencing revealed that these species harbor distinct communities of microbial flora and suggest that Acinetobacter sp. might be used in developing anti-transmission strategies.

Biting flies have been suggested as mechanical vectors of vesicular stomatitis New Jersey Virus (family Rhabdoviridae, genus Vesiculovirus, VSNJV) in livestock populations during epidemic outbreaks in the western United States. We conducted a proof-of-concept study to determine whether biting flies could mechanically transmit VSNJV to livestock by using a black fly, Simulium vittatum Zetterstedt (Diptera: Simuliidae), domestic swine, Sus scrofa L., model. Black flies mechanically transmitted VSNJV to a naïve host after interrupted feeding on a vesicular lesion on a previously infected host. Transmission resulted in clinical disease in the naïve host. This is the first demonstration of mechanical transmission of VSNJV to livestock by insects.

In Reunion Island, the distribution of the domestic form of Aedes aegypti (L.) has been restricted to natural habitats, in ravines located on the driest west coast over the past 50 yr. It is mainly found in rock holes, where it principally co-occurs with Aedes albopictus (Skuse), the most common Aedes species and the major vector of arboviruses there. To document and understand the changes in Ae. aegypti distribution on the island since the beginning of the 20th century, data on its distribution from 1985 to 1986 and from 2007 to 2008 were analyzed and compared with previously published reports. The results show that the number of breeding sites with Ae. aegypti and the relative abundance of this species have progressively decreased and that this species is not found anymore in artificial containers. The causes of the decrease of Ae. aegypti populations are discussed. It is suggested that ecological factors such as a competitive interactions between Ae. aegypti and Ae. albopictus might have triggered the decrease of Ae. aegypti observed during the fifties and that vector control campaigns during these years might have accelerated this process.