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Nelms B.M.,University of California at Davis | Kothera L.,Centers for Disease Control and Prevention | Thiemann T.,Pacific University in Oregon | Macedo P.A.,Sacramento Yolo Mosquito and Vector Control District | And 2 more authors.
American Journal of Tropical Medicine and Hygiene | Year: 2013

The vector competence and bionomics of Culex pipiens form pipiens L. and Cx. pipiens f. molestus Forskäl were evaluated for populations from the Sacramento Valley. Both f. pipiens and f. molestus females became infected, produced disseminated infections, and were able to transmit West Nile virus. Form molestus females also transmitted West Nile virus vertically to egg rafts and F1 progeny, whereas f. pipiens females only transmitted to egg rafts. Culex pipiens complex from urban Sacramento blood-fed on seven different avian species and two mammalian species. Structure analysis of blood-fed mosquitoes identified K = 4 genetic clusters: f. molestus, f. pipiens, a group of genetically similar hybrids (Cluster X), and admixed individuals. When females were exposed as larvae to midwinter conditions in bioenvironmental chambers, 85% (N = 79) of aboveground Cx. pipiens complex females and 100% (N = 34) of underground f. molestus females did not enter reproductive diapause. Copyright © 2013 by The American Society of Tropical Medicine and Hygiene.

Pellegrini A.R.,University of California at Davis | Wright S.,Sacramento Yolo Mosquito and Vector Control District | Reisen W.K.,University of California at Davis | Treiterer B.,Stone Lakes National Wildlife Refuge | Ernest H.B.,University of California at Davis
Condor | Year: 2011

From 2001 to 2008, we estimated probabilities of survival and encounter of adult House Finches (Carpodacus mexicanus) breeding at Stone Lakes National Wildlife Refuge, Sacramento County, California, from capture-recapture data on birds trapped with mist nets and ground traps. Our primary objectives were to determine when West Nile virus (WNV, Flaviviridae, Flavivirus) arrived at the site and if survivorship changed after this arrival. We monitored viral activity by screening blood samples from House Finches for WNV antibodies with an enzyme immunoassay and by testing mosquito pools for viral RNA. WNV arrived after the breeding season in late 2004, so we compared data from 2001-2004 (pre-WNV) to that from 2005-2008 (post-WNV). We found a decrease in annual survival following the arrival of WNV (pre-WNV, 0.59; post WNV, 0.47), which, if representative, may have contributed to the reported decline in the abundance of this species in northern California. Copyright © The Cooper Ornithological Society 2011.

Nelms B.M.,University of California at Davis | MacEdo P.A.,Sacramento Yolo Mosquito and Vector Control District | Kothera L.,Centers for Disease Control and Prevention | Savage H.M.,Centers for Disease Control and Prevention | Reisen W.K.,University of California at Davis
Journal of Medical Entomology | Year: 2013

At temperate latitudes, Culex (Diptera: Culicidae) mosquitoes typically overwinter as adult females in reproductive arrest and also may serve as reservoir hosts for arboviruses when cold temperatures arrest viral replication. To evaluate their role in the persistence of West Nile virus (WNV) in the Sacramento Valley of California, the induction and termination of diapause were investigated for members of the Culex pipiens (L.) complex, Culex tarsalis Coquillett, and Culex stigmatosoma Dyar under field, seminatural, and experimental conditions. All Culex spp. remained vagile throughout winter, enabling the collection of 3,174 females and 1,706 males from diverse habitats during the winters of 2010-2012. Overwintering strategies included both quiescence and diapause. In addition, Cx. pipiens form molestus Forskäl females remained reproductively active in both underground and aboveground habitats. Some blood-fed, gravid, and parous Cx. tarsalis and Cx. pipiens complex females were collected throughout the winter period. Under both field and experimental conditions, Cx. tarsalis and Cx. stigmatosoma females exposed to autumnal conditions arrested primary follicular maturation at previtellogenic stage I, with primary to secondary follicular ratios <1.5 (indicative of a hormonally induced diapause). In contrast, most Cx. pipiens complex females did not enter reproductive diapause and ovarian follicles matured to ≥stage I-II (host-seeking arrest) or were found in various stages of degeneration. Diapause was initiated in the majority of Cx. tarsalis and Cx. stigmatosoma females by mid-late October and was terminated after the winter solstice, but hostseeking seemed limited by temperature. An accrual of 97.52 ± 30.7 and 162.85 ± 79.3 degree-days after the winter solstice was estimated to be necessary for diapause termination in Cx. tarsalis under field and seminatural conditions, respectively. An increase in the proportion of blood-fed Culex females in resting collections occurred concurrently with diapause termination in field populations based on ovarian morphometrics. WNV RNA was detected in one pool of 18 males and in a single blood-fed female Cx. tarsalis collected during winter. Therefore, both vertically and horizontally infected Culex females may persist through winter and possibly transmit WNV after diapause termination in late winter or early spring in the Sacramento Valley of California. © 2013 Entomological Society of America.

Wright S.A.,Sacramento Yolo Mosquito and Vector Control District | Tucker J.R.,Vector Borne Disease Section | Donohue A.M.,Napa Mosquito Abatement District | Castro M.B.,Vector Borne Disease Section | And 3 more authors.
Journal of Medical Entomology | Year: 2011

Larval and nymphal western blacklegged tick, Ixodes pacifiais Cooley & Kohls (Acari: Ixodidae), were collected from birds, rodents, and lizards at Quail Ridge Reserve located in Napa County in northwestern California. Species from three vertebrate classes were sampled simultaneously from two transects during two consecutive spring seasons. Feeding larval and nymphal ticks were removed and preserved for counting, examination and testing for the presence of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner. Mean infestations with I. pacificus subadults on lizards were 10.0, on birds 2.9, and on rodents 1.3. I. pacificus larvae (204) collected from 10 avian species and (215) collected from two rodent species were tested for the presence of B. burgdorferi s.s. via real-time polymerase chain reaction. Three B. burgdorferi-infected larvae were taken from two Junco hyemalis and two infected larvae from one Neotoma fuscipes Baird. This is the first reported detection of B. burgdorferi in larvae feeding on a bird in western North America. © 2011 Entomological Society of America.

Dingler R.J.,University of California at Davis | Wright S.A.,Sacramento Yolo Mosquito and Vector Control District | Donohue A.M.,Napa Mosquito Abatement District | Macedo P.A.,Sacramento Yolo Mosquito and Vector Control District | Foley J.E.,University of California at Davis
Ticks and Tick-borne Diseases | Year: 2014

We investigated the involvement of birds in the ecology of the western black-legged tick, Ixodes pacificus, and its associated zoonotic bacteria, Borrelia burgdorferi and Anaplasma phagocytophilum, at two interior coast-range study sites in northern California. Anaplasma phagocytophilum, the agent of granulocytic anaplasmosis (GA), and B. burgdorferi s.s., the agent of Lyme disease (LD), are tick-borne pathogens that are well established in California. We screened blood and ticks from 349 individual birds in 48 species collected in 2011 and 2012 using pathogen-specific PCR. A total of 617 immature I. pacificus was collected with almost three times as many larvae than nymphs. There were 7.5 times more I. pacificus at the Napa County site compared to the Yolo County site. Two of 74 (3%) nymphal pools from an Oregon junco ( Junco hyemalis) and a hermit thrush ( Catharus guttatus) and 4 individual larvae (all from Oregon juncos) were PCR-positive for B. burgdorferi. Blood samples from a golden-crowned sparrow ( Zonotrichia atricapilla) and a European starling ( Sturnus vulgaris) were positive for A. phagocytophilum DNA at very low levels. Birds that forage on ground or bark and nest on the ground, as well as some migratory species, are at an increased risk for acquiring I. pacificus. Our findings show that birds contribute to the ecologies of LD and GA in California by serving as a blood-meal source, feeding and transporting immature I. pacificus, and sometimes as a source of Borrelia infection. © 2014 Elsevier GmbH.

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