Four field populations and four laboratory colonies of Culex tarsalis from California were evaluated for their susceptibility to infection with western equine encephalomyelitis (WEE) virus by intrathoracic inoculation and by feeding on pledgets soaked with a virus-blood-sucrose mixture. All mosquito strains were uniformly susceptible to infection by intrathoracic inoculation, but 50% infective doses for field and colonized strains varied as much as 1000- to 1500-fold, respectively, by pledget feeding. Moreover, dose-response curves obtained by pledget feeding revealed that some field and laboratory strains of C. tarsalis were quite heterogeneous for susceptibility since some individual females could be infected after ingestion of small concentrations of virus and others could not 0e infected by increasing the concentration of virus by 1000- to 10,000-fold. Variability in viral susceptibility of different mosquito strains could not be correlated with differences in autogeny rates or organophosphorus insecticede resistance.
Can. Ent. 118: 1185Ent. 118: -1191Ent. 118: (1986 Oxydemeton-methyl, azinphosmethyl, dimethoate, and acephate were evaluated in Douglas-fir seed orchards for control of Douglas-fir cone gall midge, Contarinia oregonensis Foote, and Douglas-fir seed chalcid, Mepsrigmus spermotrophus Wachtl. Results varied with infestation levels and specific chemicals. There was no significant reduction of infestation levels of either insect with the application of acephate. Oxydemeton-methyl injections. oxydemeton-methyl spray, and dimethoate significantly reduced cone gall midge damage. All four chemicals were ineffective against the seed chalcid for infestations of less than 10% of extractable seed. Oxydemeton-methyl injections, azinphosmethyl, and dimethoate significantly reduced the incidence of seed chalcid when the infestation was high (61%). There was no statistically significant difference (a = 0.05) for painvise comparisons between chemicals which significantly reduced the infestation levels of either insect.On a test6 l'oxyd6meton-mkthyle, I'azinphosmCthyle, le dimethoate et l'acephate dans des plantations de semence du sapin Douglas, contre la ckcidomie des canes du Douglas, Contarinia oregonensis Foote, et le chalcis du Douglas, Megastigrnus sperrnotrophus Wachtl. Les rksultats ont varik selon les niveaux d'infestation et les produits utilids. Aucune rkduction significative des niveaux d'infestation de l'un ou I'autre nuisible n'a tt6 observk avec I'acQhate. Des injections d'oxydtmtton-rnCthyIe. un arrosage 2 I'oxydtm6ton-mtthyle, et le dimethoate ont r a u i t significativement les dommages causds par la ckcidomie des canes du Douglas. Les quaue produits se sont avCds inefficaces contre le chalcis aux niveaux d'infestation infkrieurs li 10% des graines extractibles. Des injections d'oxydkmtton-methyle, I'azinphosmtthyle et Ie dimkthoate ont M u i t significativement I'incidence du chalcis lorsque I'infestation ttait Gvkre (61%). On n'a pas observe de difference significative (a =0.05) enue les produits qui ont &hit signifcativement les infestations de I'un ou I'autre insecte, sur la base de comparaisons pairkes .
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