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A protein-electrophoretic analysis of six putative morphospecies in the bivalve family Vesicomyidae from eight deep-sea hydrothermal vent sites in the eastern Pacific, three cold-water seep sites in the eastern Pacific and the Gulf of Mexico, and one whale-carcass site off Southern California revealed electromorph patterns diagnostic of 10 vesicomyid species. Electrophoretic patterns for 14 enzymes encoded by 17 presumptive gene loci were scored in all 10 species. The pairwise genetic distances (Nei's D) for these 10 species ranged from 0.857 to 2.792, values within the range expected for distinct species and genera. However, the degree of genetic divergence among these taxa could not be used for phylogenetic inferences because allozyme differences had in many cases reached evolutionary saturation. Notwithstanding, the present results revealed a significant problem with current morphospecies identifications of these clams and with applications of the current generic names Calyptogena and Vesicomya. Given the cryptic nature of these taxa, we suggest that subsequent studies simply refer to these clams as “vesicomyids” until careful morphological analyses and molecular studies are completed and systematic relationships are clarified.

Nearly 80,000 immature and adult mosquitoes in three genera were collected in high-elevation (> 1,000 m) areas of California (68,229), Nevada (3,721), Oregon (5,918), and Washington (1,629) during 1990-1992 and tested for virus as adult males or females in 1,799 pools. Collections comprised primarily alpine Aedes in the Aedes communis (De Geer) group of the subgenus Ochlerotatus. Thirteen strains of Jamestown Canyon (JC) virus were recovered by plaque assay in Vero cell culture from three members of the Ae. communis group: 10 from Aedes tahoensis Dyar, 2 from Aedes cataphylla Dyar, and 1 from Aedes hexodontus Dyar. All isolates came from collections made in Alpine, Sierra, Tulare, or Tuolumne counties in the Sierra Nevada of California. Vertical transmission of JC virus in all three mosquito species was demonstrated by the isolation of virus from adult males or females reared from field-collected larvae or pupae. The prevalence of infected Ae. tahoensis was significantly higher in field-collected adult females than in reared adult males and females in Alpine County, which indicated that JC virus was being amplified by horizontal transmission. This study further incriminated Ae. tahoensis, Ae. cataphylla, and Ae. hexodontus as natural vectors of JC virus in California and greatly extended the known geographical range of this virus in the Sierra Nevada.

The salt marsh horse fly, Tabanus nigrovittatusMacquart, exhibits two nonoverlapping daily periods of hovering and mating activity, which are correlated with different environmental temperatures. Allelic and genotypic frequencies of hovering males collected during the two periods were compared by electrophoresis of three polymorphic enzyme loci. Approximately 26% of early-hovering males possessed a Pgmallozyme that was absent in our sample of late-hovering males. However, based on other allozyme loci, we found no evidence for reproductive isolation between early and late hoverers. All the genetic data are consistent with the hypothesis that the Pgmpolymorphism is associated with behaviorally and physiologically distinct groups of males that, by all other criteria, form a single Mendelian population.

Hovering aggregations of male salt marsh greenheads Tabanus nigrovittatusand the sibling species T. conterminuswere observed on marshes in southern New Jersey. T. nigrovittatusmales hovered over expanses of short marsh grasses, while T. conterminushovered over tidal creeks and near other prominent landmarks. T. nigrovittatusexhibited two distinct daily hovering periods. The timing of these periods varied daily but showed a strong negative correlation with ambient temperature. A principal-components analysis identified a combination of ambient temperature, black-body temperature, and light intensity as most predictive of hovering onset. T. conterminushovered during a time period which was generally intermediate to the two hovering periods of T. nigrovittatus.Temporal partitioning of hovering “windows” may represent a premating isolating mechanism.

A population-genetic study of adult female Tabanus lineola F. from New Jersey and Louisiana determined that the coastal and inland “varieties” T. lineola hinellus Philip and T. lineola lineola F. are reproductively isolated and represent distinct species. Diagnostic differences were found at 4 of 11 gene loci surveyed. Nine individuals were genetically distinct from all other specimens and may represent a third cryptic species. Stepwise discriminant analysis was used to produce a taxonomic key for separation of the coastal and inland species based on four easily measured morphological characters. The degree of separation achieved was greater for specimens collected in Louisiana.

Salt marsh horse flies were observed feeding on aphid honeydew located on the leaves of marsh elder, Iva frutescens L. Most feeding individuals were males. Onset of feeding activity of Tabanus nigrovittatus Macquart occurred when hovering and mating activity ended. Because males and females have not been observed previously to feed on floral nectar, honeydew may represent a major source of carbohydrates for flight.