Entity

Time filter

Source Type


Su T.,West Valley Mosquito and Vector Control District | Cheng M.-L.,West Valley Mosquito and Vector Control District
Journal of Medical Entomology | Year: 2014

ABSTRACT A southern house mosquito Culex quinquefasciatus Say colony was established from surviving late instars and pupae from a semifield evaluation on Natular XRG (a granular formulation containing 2.5% spinosad). The initial lethal levels of Natular XRG against this colony were determined in the laboratory for the first-generation progeny (designated as F1). Selection pressure was applied at LC70-90 levels to 10,000-15,000 late third- and early fourth-instar larvae of each generation with Natular XRG. Susceptibility changes in response to selection were determined every other generation, where a gradual and steady decline in susceptibility occurred from generation F1 to F35, followed by significant decline from generations F37 to F45 For reference purposes, susceptibility of freshly collected wild populations as well as a laboratory colony of the same species was also determined concurrently, which fluctuated within a slightly wider range for the wild populations and a tighter range for the laboratory colony. By comparing with wild populations and laboratory reference colony, tolerance to spinosad was observed from generations up to F9 in the selected population. Resistance levels increased gradually from generation F11 to F35, and elevated significantly from generations F37 to F45 when resistance ratios reached 1,415.3- to 2,229.9-fold at LC50 and 9,613.1- to 17,062.6-fold at LC90 Possible mechanisms of resistance development to spinosad were discussed. © 2014 Entomological Society of America. Source


Cheng M.-L.,West Valley Mosquito and Vector Control District | Su T.,West Valley Mosquito and Vector Control District
Journal of the American Mosquito Control Association | Year: 2011

A novel test procedure can screen seroconversions in sentinel chickens with the commercially available VecTest® designed to detect viral antigens, such as West Nile virus. The test requires minimum laboratory equipment and skills, and provides qualitative results in about 45 min, which are immediately available to vector control agencies for making decisions to manage mosquito populations in order to interrupt arbovirus transmission. © 2011 by The American Mosquito Control Association, Inc. Source


Su T.,West Valley Mosquito and Vector Control District | Cheng M.-L.,West Valley Mosquito and Vector Control District
Journal of Medical Entomology | Year: 2014

ABSTRACT A Culex quinquefasciatus Say colony was selected for 45 generations at LC70-90 levels using Natular XRG, a granular formulation of 2.5% spinosad for induction of spinosad resistance. Resistance to spinosad was noticed in early generations (F1-F9). Resistance levels increased gradually from generations F11-F35, and elevated significantly from generation F37 through F47. when resistance ratios reached 2,845-2,907-fold at LC50 and 11,948-22,928-fold at LC90 The spinosad-resistant Cx. quinquefasciatus colony was found not to be cross-resistant to Bacillus thuringiensis israelensis (Bti), a combination of Bti and Bacillus sphaericus, methoprene, pyriproxyfen, diflubenzuron, novaluron, temephos, or imidacloprid. However, it showed various levels of cross-resistance to B. sphaericus, spinetoram, abamectin, and fipronil. Conversely, a laboratory colony of Cx. quinquefasciatus that is highly resistant to B. sphaericus did not show cross-resistance to spinosad and spinetoram. Field-collected and laboratory-selected Cx. quinquefasciatus that showed low to moderate resistance to methoprene did not show cross-resistance to spinosad and spinetoram. Mechanisms of cross-resistance among several biorational pesticides were discussed according to their modes of actions. © 2014 Entomological Society of America. Source


Molaei G.,Center for Vector Biology and Zoonotic Diseases | Su T.,West Valley Mosquito and Vector Control District | Armstrong P.M.,Center for Vector Biology and Zoonotic Diseases | Williams G.A.,Northwest Mosquito and Vector Control District | And 2 more authors.
American Journal of Tropical Medicine and Hygiene | Year: 2010

Southern California remains an important focus of West Nile virus (WNV) activity, with persistently elevated incidence after invasion by the virus in 2003 and subsequent amplification to epidemic levels in 2004. Eco-epidemiological studies of vectors-hosts-pathogen interactions are of paramount importance for better understanding of the transmission dynamics of WNV and other emerging mosquito-borne arboviruses. We investigated vector-host interactions and host-feeding patterns of 531 blood-engorged mosquitoes in four competent mosquito vectors by using a polymerase chain reaction (PCR) method targeting mitochondrial DNA to identify vertebrate hosts of blood-fed mosquitoes. Diagnostic testing by cell culture, real-time reverse transcriptase-PCR, and immunoassays were used to examine WNV infection in blood-fed mosquitoes, mosquito pools, dead birds, and mammals. Prevalence of WNV antibodies among wild birds was estimated by using a blocking enzyme-linked immunosorbent assay. Analyses of engorged Culex quinquefasciatus revealed that this mosquito species acquired 88.4% of the blood meals from avian and 11.6% from mammalian hosts, including humans. Similarly, Culex tarsalis fed 82% on birds and 18% on mammals. Culex erythrothorax fed on both birds (59%) and mammals (41%). In contrast, Culex stigmatosoma acquired all blood meals from avian hosts. House finches and a few other mostly passeriform birds served as the main hosts for the blood-seeking mosquitoes. Evidence of WNV infection was detected in mosquito pools, wild birds, dead birds, and mammals, including human fatalities during the study period. Our results emphasize the important role of house finches and several other passeriform birds in the maintenance and amplification of WNV in southern California, with Cx. quinquefasciatus acting as both the principal enzootic and "bridge vector" responsible for the spillover of WNV to humans. Other mosquito species, such as Cx. tarsalis and Cx. stigmatosoma, are important but less widely distributed, and also contribute to spatial and temporal transmission of WNV in southern California. Copyright © 2010 by The American Society of Tropical Medicine and Hygiene. Source


Su T.,West Valley Mosquito and Vector Control District | Cheng M.-L.,West Valley Mosquito and Vector Control District
Journal of the American Mosquito Control Association | Year: 2012

A Culex quinquefasciatus colony was established from surviving late instars and pupae from a semifield microcosm test with Natular® XRG (a granular formulation containing 2.5 spinosad) applied at 14.2 kg/ha. The initial lethal concentrations for 50 and 90 of the population (LC50 and LC 90) against Natular XRG were determined in the laboratory for the 1st generation progeny (F1). Selection was applied at LC70-90 levels to 10,00015,000 of late 3rd and early 4th instars each generation. Susceptibility changes were determined every other generation and referenced to a susceptible laboratory colony as well as freshly collected wild populations of the same species concurrently. Tolerance to spinosad (resistance ratio <5.0 fold) was observed up to F8 generation in the selected population. Thereafter, resistance ratios increased significantly from F10 to F16 generations, being 7.26-to 20.52-fold at the LC50 and 7.48-to 20.08-fold at the LC90 level. © 2012 by The American Mosquito Control Association, Inc. Source

Discover hidden collaborations