Identification of quantitative trait loci affecting sex determination in the Eastern treehole mosquito (Ochlerotatus triseriatus). (1/30)

Laboratory colonies of the eastern treehole mosquito (Ochlerotatus triseriatus (Say)) exhibit a consistent female-biased sex ratio. This is unusual among mosquito species, in which heritable sex ratio distortion is usually male biased and mediated by meiotic drive. Quantitative trait loci (QTL) affecting sex were mapped in an F(1) intercross to better understand the genetics underlying this female bias. In P(1) and F(1) parents and in 146 F(2) individuals with a female-biased sex ratio (106 females:40 males), regions of seven cDNA loci were analyzed with single-strand conformation polymorphism (SSCP) analysis to identify and orient linkage groups. Genotypes were also scored at 73 random amplified polymorphic DNA (RAPD)-SSCP loci. In addition to the sex locus, at least four QTL affecting sex determination were detected with interval mapping on linkage groups I and II. Alleles at the sex locus cumulatively accounted for approximately 61-77% of the genetic variance in sex. Alleles at QTL adjacent to the sex locus and at a QTL on the opposite end of linkage group I increased the proportion of females, but alleles at a QTL on linkage group I and a second QTL on linkage group II increased the proportion of males. The female-biased sex ratio observed in laboratory colonies of O. triseriatus is most easily explained by the existence of multiple female biased distorter loci, as have been observed in other Diptera.  (+info)

Field detection of eastern equine encephalitis virus in the Amazon Basin region of Peru using reverse transcription-polymerase chain reaction adapted for field identification of arthropod-borne pathogens. (2/30)

In support of efforts to develop rapid diagnostic assays for use in the field, reverse transcription-polymerase chain reaction (RT-PCR) assays were developed to detect arboviruses circulating in the Amazon Basin region of Peru. Previous knowledge of arthropod/pathogen relationships allowed a focused evaluation to be conducted in November 2000 that assessed the feasibility and reliability of a mobile, rapid, field-expedient RT-PCR diagnostic system aimed at detecting eastern equine encephalitis virus (EEEV) in Culex (Melanoconion) pedroi mosquitoes. Modifications were made to a commercially available mobile molecular laboratory kit and assay procedures were tailored for use under harsh environmental conditions with field-collected and field-processed mosquitoes. From CO2 baited mosquito light traps, 3,227 Cx. (Mel.) pedroi mosquitoes were collected and sorted into 117 pools. The pools were processed and assayed in the field by RT-PCR and five of those pools were found positive for EEEV. Laboratory sequence analysis confirmed the presence of two distinct subtypes of EEEV.  (+info)

Differences in the effects of salinity on larval growth and developmental programs of a freshwater and a euryhaline mosquito species (Insecta: Diptera, Culicidae). (3/30)

The effects of salinity on growth and development of the euryhaline Ochlerotatus taeniorhynchus and the freshwater Aedes aegypti are compared. O. taeniorhynchus grow larger, and have greater intrinsic growth rates, than A. aegypti. Females of each species attain greater mass, take longer to develop, and have greater growth rates than do males. In O. taeniorhynchus, pupal mass, larval stage duration and growth rates (dry mass) increase with salinity, whereas growth rates (wet mass) remain constant across salinities, reflecting a decrease in percent body water. The pupal mass (wet or dry) of O. taeniorhynchus is determined primarily by effects of salinity on the rate of assimilation of dry mass, because the latter contributes very strongly to final pupal mass in both species. In contrast, the duration of A. aegypti larval stage follows a upsilon-shaped curve, with most rapid development at intermediate salinities. Growth rates of A. aegypti decrease with increasing salinity, and percent body water is constant across salinities. As for O. taeniorhynchus, duration of A. aegypti larval stage increases at high salinity. However, this increase in larval stage duration cannot compensate for the decrease in growth rate at high salinity, resulting in an overall decrease in both wet and dry pupal mass at high salinity. Thus, salinity has fundamentally different effects on developmental programs and phenotypic plasticity in the two species investigated.  (+info)

pH tolerances and regulatory abilities of freshwater and euryhaline Aedine mosquito larvae. (4/30)

The pH regulatory abilities of two members of the mosquito tribe Aedini, known to have dramatically different saline tolerances, are investigated. The freshwater mosquito Aedes aegypti and the euryhaline Ochlerotatus taeniorhynchus tolerate very similar pH ranges. Both species complete larval development in waters ranging from pH 4 to pH 11, but naive larvae always die in water of pH 3 or 12. Across the pH range 4-11, the hemolymph pH of O. taeniorhynchus is maintained constant while that of A. aegypti varies by 0.1 pH units. The salt composition of the water (3.5 g l(-1) sea salt, 3.5 g l(-1) NaCl, or nominally salt-free) has no effect on the range of pH tolerated by A. aegypti. In both species, the effects of pH on larval growth and development are minor in comparison with the influence of species and sex. Acclimation of A. aegypti to pH 4 or 11 increases survival times in pH 3 or 12, respectively, and allows a small percentage of larvae to pupate successfully at these extreme pH values. Such acclimation does not compromise survival at the other pH extreme.  (+info)

Venezuelan equine encephalitis emergence: enhanced vector infection from a single amino acid substitution in the envelope glycoprotein. (5/30)

In 1993 and 1996, subtype IE Venezuelan equine encephalitis (VEE) virus caused epizootics in the Mexican states of Chiapas and Oaxaca. Previously, only subtype IAB and IC VEE virus strains had been associated with major outbreaks of equine and human disease. The IAB and IC epizootics are believed to emerge via adaptation of enzootic (sylvatic, equine-avirulent) strains for high titer equine viremia that results in efficient infection of mosquito vectors. However, experimental equine infections with subtype IE equine isolates from the Mexican outbreaks demonstrated neuro-virulence but little viremia, inconsistent with typical VEE emergence mechanisms. Therefore, we hypothesized that changes in the mosquito vector host range might have contributed to the Mexican emergence. To test this hypothesis, we evaluated the susceptibility of the most abundant mosquito in the deforested Pacific coastal locations of the VEE outbreaks and a proven epizootic vector, Ochlerotatus taeniorhynchus. The Mexican epizootic equine isolates exhibited significantly greater infectivity compared with closely related enzootic strains, supporting the hypothesis that adaptation to an efficient epizootic vector contributed to disease emergence. Reverse genetic studies implicated a Ser --> Asn substitution in the E2 envelope glycoprotein as the major determinant of the increased vector infectivity phenotype. Our findings underscore the capacity of RNA viruses to alter their vector host range through minor genetic changes, resulting in the potential for disease emergence.  (+info)

Quantitative genetics of vector competence for La Crosse virus and body size in Ochlerotatus hendersoni and Ochlerotatus triseriatus interspecific hybrids. (6/30)

La Crosse virus is a leading cause of pediatric encephalitis in the United States. The mosquito Ochlerotatus triseriatus is an efficient vector for La Crosse virus, whereas the closely related O. hendersoni transmits only at very low rates. Quantitative trait loci (QTL) affecting the ability to orally transmit this virus and adult body size were identified in 164 F(2) female individuals from interspecific crosses of O. hendersoni females and O. triseriatus males using a combination of composite interval mapping (CIM), interval mapping (IM) for binary traits, and single-marker mapping. For oral transmission (OT), no genome locations exceeded the 95% experimentwise threshold for declaring a QTL using IM, but single-marker analysis identified four independent regions significantly associated with OT that we considered as tentative QTL. With two QTL, an increase in OT was associated with alleles from the refractory vector, O. hendersoni, and likely reflect epistatic interactions between genes that were uncovered by our interspecific crosses. For body size, two QTL were identified using CIM and a third tentative QTL was identified using single-marker analysis. The genome regions associated with body size also contain three QTL controlling OT, suggesting that these regions contain either single genes with pleiotropic effects or multiple linked genes independently determining each trait.  (+info)

Larval feeding behavior of three co-occurring species of container mosquitoes. (7/30)

Interspecific differences in foraging behavior may help to determine whether the outcome of interspecific competition is coexistence or exclusion. Mosquitoes in the genus Culex are commonly described as foraging primarily by filtering the water column. This behavior contrasts with that of other container-dwelling genera, such as Aedes and Ochlerotatus, that are thought to forage primarily by browsing on container and detritus surfaces. We compared the feeding behavior of Cx. pipiens, Ae. albopictus, and Oc. triseriatus in a laboratory experiment in which we monitored behavior of individual mosquitoes in two different food environment treatments: food suspended in the water column only and food attached to leaf surfaces only. For each mosquito in each food environment, we quantified the time allocated by larvae to one of four positions and to one of three activities. The effect of treatment was significant, with individuals in Fluid Only environments spending more time resting-filtering at the surface, and individuals in Leaf Only environments spending more time browsing on walls. There were significant differences among species, with Cx. pipiens spending more time at the surface than the other species, which spent more time thrashing below the surface. There was no significant interaction of species and treatment, indicating that all three species modify their behavior in similar ways in these environments. Contrary to current understanding, our data suggest that Cx. pipiens browse as frequently as do these potential competitors but show a greater concentration of foraging effort at the top of a container.  (+info)

Preliminary evidence of association between species of mosquitoes in Atlantic forest of Santa Catarina State, (Diptera: Culicidae). (8/30)

A positive coefficient of association (affinity) between Runchomyia reversa and Anopheles cruzii and high (0.38) index were observed, probably due to the similar breeding places (bromeliads) and to landing habits. Furthermore, a high (0.92) index of association between Oc. scapularis and Wyeomyia incaudata, with low coefficient of association was observed.  (+info)

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