A detailed larval salivary gland polytene chromosome photomap for Culex quinquefasciatus (Diptera: Culicidae) from Johannesburg, South Africa.

The suitability of polytene chromosomes for population genetic and in situ DNA physical mapping was investigated in Johannesburg, South Africa, Culex quinquefasciatus Say and Culex pipiens L.. The most defined and consistent polytene spreads were obtained from salivary glands of early fourth instars from Cx. quinquefasciatus. A photomap is provided for a Cx. quinquefasciatus colony originating from Johannesburg. Variations in banding patterns, chromosome aberrations, and paracentric inversions within the colony and comparisons with previous published descriptions are discussed. Chromosomes of sufficient quality were obtained such that a DNA coding for an odorant binding protein could be mapped by colorimetric in situ hybridization.

Effects of lambda-cyhalothrin on mosquito larvae and predatory aquatic insects.

Agricultural insecticides can affect mosquito production in rice fields by controlling mosquitoes, disrupting biological control or contributing to selection of insecticide resistance. The duration of insecticidal activity of the pyrethroid lambda-cyhalothrin was quantified on predatory insects in rice fields and on three kinds of mosquito larva: a pyrethroid-susceptible strain of Culex tarsalis Coquillet, a pyrethroid-resistant strain of Cx pipiens L. (sensu lato) and non-resistant Cx pipiens s.l. Lambda-cyhalothrin killed most caged, susceptible mosquitoes for up to 21 days. It killed fewer resistant Cx pipiens s.l., but suppressed their survival for over a week. Lambda-cyhalothrin suppressed field populations of predatory insects through day 29. Agricultural use of lambda-cyhalothrin can provide incidental mosquito control. However, the pyrethroid persisted in sediment and gradually decreased in activity, which could contribute to selection of pyrethroid-resistant mosquitoes. Because caged mosquitoes showed good survival before predators recovered, disruption of biological control is possible. It is therefore advisable for growers and mosquito control agencies to communicate about pesticide use.

Development of a HPLC/tandem-MS method for the analysis of the larvicides methoprene, hydroprene, and kinoprene at trace levels using Diels-Alder derivatization.

The invasion and subsequent spread of the mosquito-borne West Nile virus in the United States has resulted in increased use of methoprene. With the increased need for sensitive detection and monitoring of methoprene in the environment, an analytical LC/ESI-MS/MS method has been developed for the analysis of methoprene and two analogues, kinoprene and hydroprene, in water. To improve the ionization efficiency of the nonpolar analytes, a derivatization step with the Cookson-type reagent 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) was used. Derivatization improved the limit of detection 100-fold. For tandem MS analyses, limits of detection in environmental water samples (S/N = 3) are about 6 pg/mL for methoprene and 20 pg/mL for kinoprene and hydroprene, resulting in limits of quantification (S/N = 10) of 20 pg/mL for methoprene and 60 pg/mL for hydroprene and kinoprene extracted from 10 mL of water. This method was applied to measure methoprene concentrations in water samples from a treated site.

Pyrethroid tolerance in Culex pipiens pipiens var molestus from Marin County, California.

In May 2001 a sample of Culex pipiens pipiens variety molestus Forskål from Marin County, California, collected as larvae and reared to adults, was found to show reduced resmethrin and permethrin knock-down responses in bottle bioassays relative to a standard susceptible Cx. pipiens quinquefasciatus Say colony (CQ1). Larval susceptibility tests, using CQ1 as standard susceptible, indicated that the Marin mosquitoes had LC50 resistance ratios of 18.3 for permethrin, 12 for deltamethrin and 3.3 for pyrethrum. A colony of Marin was established and rapidly developed higher levels of resistance in a few generations after exposure to permethrin as larvae. These selected larvae were shown to cross-resist to lambda-cyhalothrin as well as to DDT. However, adult knock-down time in the presence of permethrin, resmethrin and pyrethrum was not increased after increase in tolerance to pyrethroids as larvae. Partial and almost complete reversion to susceptibility as larvae was achieved with S, S, S-tributylphosphorotrithioate and piperonyl butoxide (PBO), respectively, suggesting the presence of carboxylesterase and P450 monooxygenase mediated resistance. Insensitive target site resistance (kdr) was also detected in some Marin mosquitoes by use of an existing PCR-based diagnostic assay designed for Cx. p. pipiens L mosquitoes. Carboxylesterase mediated resistance was supported by use of newly synthesized novel pyrethroid-selective substrates in activity assays. Bottle bioassays gave underestimates of the levels of tolerance to pyrethroids of Marin mosquitoes when compared with mortality rates in field trials using registered pyrethroid adulticides with and without PBO. This study represents the first report of resistance to pyrethroids in a feral population of a mosquito species in the USA.

Role of esterase enzymes in monitoring for resistance of California red scale, Aonidiella aurantii (Homoptera: Diaspididae), to organophosphate and carbamate insecticides.

Eighty-seven populations of California red scale, Aonidiella aurantii (Maskell), from the San Joaquin Valley of California were tested for insecticide resistance by using chlorpyrifos, methidathion, and/or carbaryl in a standard fruit-dip bioassay as well as for general esterase activity by using alpha-naphthyl acetate as a substrate in a colorimetric test. The percentage of individuals that survived a discriminating concentration of methidathion, chlorpyrifos, or carbaryl was significantly correlated with the percentage of individuals showing > 0.4 nmol of esterase activity per minute per microgram of protein in the colorimetric test. Scale survival of the organophosphates showed a higher correlation with esterase activity than survival of carbaryl. These results suggest that the colorimetric test of esterase activity is useful as an indicator of the frequency of organophosphate-resistant and, to a lesser extent, carbamate-resistant individuals in California red scale populations. The results of tests for activity and inhibition of acetylcholinesterase activity suggest that California red scale is using increased amounts of esterase enzymes, including acetylcholinesterase, to sequester organophosphate and carbamate insecticides, rather than modified acetylcholinesterase. Third instars collected from twigs, leaves, and fruit showed similar levels of esterase activity. The colorimetric test of esterase activity is a useful tool to detect organophosphate and carbamate resistance in San Joaquin Valley California red scale because of its speed of testing over a wide range of months, allowing for within-season decision making by citrus growers.

Influence of temperature and concentration of VectoBac on control of the salt-marsh mosquito, Ochlerotatus squamiger, in Monterey County, California.

Laboratory susceptibility bioassays were conducted to determine the efficacy of VectoBac TP (Bacillus thuringiensis var. israelensis [Bti]) at different concentrations and temperatures against the salt-marsh mosquito Ochlerotatus squamiger. Bioassays on late 3rd- and early 4th-stage larvae, read at 72 h and 14 degrees C produced an LD90 of 0.223 mg/liter, whereas more than double this dose was required to produce similar mortality at 6 degrees C. A field trial in the winter of 2001-02 of an aerially applied VectoBac TP formulation in Salinas, CA, corroborated laboratory bioassay observations by producing 97-100% control of Oc. squamiger at 72 h postapplication. Inconsistencies in mortality with field applications of VectoBac TP previously observed by North Salinas Valley Mosquito Abatement personnel were most likely caused by uneven application rates and varying temperatures and water volumes.