Previous analyses have established that host species range in the most important determinant of plant— and animal—associated parasite species richness, and that the age of a host species within a region is, at most, much less important in determining this richness. However, these previous analyses were not able to completely rule out age as a cause, because the available host age estimations were crude and few host groups were available for comparison. This paper examines the arthropod pests of sugarcane (Saccharum officinarum) in 51 regions for which dates of introduction, areas in cultivation, and associated pest data are available. The sugarcane data are more complete and extensive than those for previously investigated host—parasite associations, and they make possible a more detailed analysis of the causes of species richness. Multiple regression analyses of these data cannot identify time to have any measurable influence upon the species richness of sugarcane pests. This implies pest species accumulation to reach an asymptote within, at most, a few hundred years. The asymptote is set by the geographic range of host species. The results of this study are consistent with those of four other analyses of host—parasite associations. We suggest sufficient evidence has accumulated to justify abandoning nonasymptotic species accumulation models (the "time) and "stability—time" hypotheses), at least for parasite communities. We caution against invoking "time" hypotheses for the explanation of diversity variation in other ecological systems where the influence of area and immigration rates cannot be dealt with. The "time" hypothesis also often involves virtually untestable assumptions about habitat constancy over very long periods of time.

Oviposition traps set in rural to urban environments in three south Florida counties were colonized predominantly by Culex quinquefasciatus Say (35.1%), Aedes albopictus (Skuse) (34.5%), Aedes aegypti (L.) (23.8%), and Culex nigripalpus Theobald (6.6%) during 1 yr of monthly sampling. Significant differences were detected among counties for abundances of Cx. quinquefasciatus and for percentage composition of that species and Ae. albopictus. Aerial images of habitats around each collection site were digitized, and coverages by each of 16 habitat variables were recorded. Abundances ofAe. aegypti were positively related to habitat variables associated with urbanization and negatively correlated to those reflecting rural characteristics. Multiple regression models of habitat selection explained similar proportions of variances in abundance of Ae. aegypti and Ae. albopictus, but signs of significant variables were opposite for these two species. No consistent trends of habitat associations were observed among counties for the two Culex spp. Co-occurrences of the four species in individual traps depended on container type (tub versus cup), and, for Aedes spp. with Culex spp., county. The results underscore the importance of scale in evaluating habitat selection and the utility of quantifiable habitat characteristics of intermediate scale to identify site characteristics favored by the arboviral vectors Ae. aegypti and Ae. albopictus.

Salt marshes of the Indian River Lagoon, Florida (USA) were once p.'olif]c producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the inflequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16,200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes.However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation fiom the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped fl'om 16 to 5 alter impounding Wetland vegetation within some impoundments was totally eliminated: other impoundments developed into freshwater systems.When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began ahnost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped intlllet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic.Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of" the year. Culverts are typically opened when the thll sea level rise first floods the high marsh. Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRk system. One stumbling block is private ownership of many of the remaining isolated impoundments.-" Uni\ersity of Florida, IFAS. Journal Series No. R-05201. ; Itarbor Branch Contribution Number II52. 94 VOLUSIA t IR ~Mkk Merritt r Island ! i. BR Impounded Wetlands in the Indian River Lagoon 9 Impoundments _ land Water KILOMETERS 0 6.43 12.8

La reciente expansión geográfica del mosquito Aedes albopictus ha estado acompañada en algunos sitios por la disminución en la abundancia o por la eliminación local de Aedes aegypti, pero las dos especies aún coexisten en extensas regiones de América. En este trabajo se ofrece un resumen de los posibles mecanismos responsables de sus patrones de abundancia y desplazamiento, así como de su significado en cuanto a la transmisión de enfermedades. Entre los mecanismos observados, se encuentran la competencia por recursos, las diferencias en la capacidad para soportar la inanición, la competencia aparente a través de efectos diferenciales del parásito Ascogregarina taiwanensis, y la inhibición causada por larvas de Ae. albopictus en el desarrollo de los huevos de Ae. aegypti. Un mecanismo propuesto como promotor de la coexistencia de estas especies es la segregación en diferentes hábitats, lo que evita la competencia directa. Aedes aegypti predomina en áreas urbanas, Ae. albopictus en áreas rurales, y las dos especies coexisten en áreas periurbanas. Existen pruebas de que la distribución de Ae. aegypti y Ae. albopictus también puede verse afectada en ciertas áreas, por la distancia desde la costa. Otra posible causa de la rápida desaparición de Ae. aegypti es la interferencia reproductiva entre las dos especies. De acuerdo con esta hipótesis, los efectos asimétricos de los apareamientos entre especies favorecen a Ae. albopictus. Este tipo de interferencia reproductiva podría ser la causante de la eliminación de poblaciones simpátricas de las especies involucradas y de la rapidez con que Ae. aegypti ha desaparecido de muchos lugares en América luego de la invasión de Ae. albopictus. Palabras clave:Aedes, arbovirus, virus chikungunya, dengue, hábitat. doi: http://dx.doi.org/10.7705/biomedica.v35i2.2514 Ecology of Aedes aegypti and Aedes albopictus in the Americas and disease transmissionThe recent range expansion of the mosquito Aedes albopictus has been associated in some areas by declines in abundance or local elimination of Aedes aegypti, but the two species still coexist in large regions of the Americas. We offer a summary of the possible mechanisms responsible for the abundance and displacement pattern observed and of their significance in terms of disease transmission. Among these mechanisms we may mention the competition for limiting resources, the differences in the ability to withstand starvation, the apparent competition through differential effects of the parasite Ascogregarina taiwanensis, and the inhibition of Ae. aegypti egg development by Ae. albopictus larvae. Habitat segregation has been proposed as a mechanism promoting the coexistence of the two species through avoidance of direct competition. Aedes aegypti predominates in urban areas, Ae. albopictus in rural ones, and both species coexist in the suburbs. There is also evidence that in certain areas, habitat segregation in terms of distance from the coast can influence the distribution of both species. Another possible cause of the rapid disappearanc...