Journal Article•
Simplification of adult mosquito bioassays through use of time-mortality determinations in glass bottles
01 Jun 1998-Journal of The American Mosquito Control Association (J Am Mosq Control Assoc)-Vol. 14, Iss: 2, pp 159-164
TL;DR: A simple method is described for treating 250-ml glass Wheaton bottles with insecticide, and using them as test chambers for detecting insecticide resistance in mosquito and sandfly populations.
Abstract: A simple method is described for treating 250-ml glass Wheaton bottles with insecticide, and using them as test chambers for detecting insecticide resistance in mosquito and sandfly populations. The methods for treating bottles, obtaining baseline data, and applying this technique to insects from the field are described. Sample data are presented from tests run on different vector species using a variety of insecticides. Time-mortality data from the bottle bioassay are presented alongside results from biochemical detection methods applied to the same mosquito population. The potential role, advantages, and limitations of the time-mortality bottle method are discussed.
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TL;DR: Finding these proportions of pyrethroid‐resistant An.
Abstract: Northern Kwazulu/Natal (KZN) Province of South Africa borders on southern Mozambique, between Swaziland and the Indian Ocean. To control malaria vectors in KZN, houses were sprayed annually with residual DDT 2 g/ m2 until 1996 when the treatment changed to deltamethrin 20-25 mg/m2. At Ndumu (27 degrees 02'S, 32 degrees 19'E) the recorded malaria incidence increased more than six-fold between 1995 and 1999. Entomological surveys during late 1999 found mosquitoes of the Anopheles funestus group (Diptera: Culicidae) resting in sprayed houses in some sectors of Ndumu area. This very endophilic-vector of malaria had been eliminated from South Africa by DDT spraying in the 1950s, leaving the less endophilic An. arabiensis Patton as the only vector of known importance in KZN. Deltamethrin-sprayed houses at Ndumu were checked for insecticide efficacy by bioassay using susceptible An. arabiensis (laboratory-reared) that demonstrated 100% mortality. Members of the An. funestus group from Ndumu houses (29 males, 116 females) were identified by the rDNA PCR method and four species were found: 74 An. funestus Giles sensu stricto, 34 An. parensis Gillies, seven An. rivulorum Leeson and one An. leesoni Evans. Among An. funestus s.s. females, 5.4% (4/74) were positive for Plasmodium falciparum by ELISA and PCR tests. To test for pyrethroid resistance, mosquito adults were exposed to permethrin discriminating dosage and mortality scored 24h post-exposure: survival rates of wild-caught healthy males were 5/10 An. funestus, 1/9 An. rivulorum and 0/2 An. parensis; survival rates of laboratory-reared adult progeny from 19 An. funestus females averaged 14% (after 1h exposure to 1% permethrin 25:75cis:trans on papers in WHO test kits) and 27% (after 30 min in a bottle with 25 microg permethrin 40:60cis:trans). Anopheles funestus families showing >20% survival in these two resistance test procedures numbered 5/19 and 12/19, respectively. Progeny from 15 of the families were tested on 4% DDT impregnated papers and gave 100% mortality. Finding these proportions of pyrethroid-resistant An. funestus, associated with a malaria upsurge at Ndumu, has serious implications for malaria vector control operations in southern Africa.
548 citations
TL;DR: Annotation of the recently determined genome sequence of the major dengue vector, Aedes aegypti, reveals an abundance of detoxification genes, and an array containing unique oligonucleotide probes for these genes was constructed and compared their expression level in insecticide resistant and susceptible strains.
319 citations
TL;DR: The tools and information presented provide a means for early detection and characterization of kdr that is critical to the development of strategies for resistance management and showed a high rate of recombination even though the two codons are only separated by a ~250 bp intron.
Abstract: Pyrethroids are commonly used as mosquito adulticides and evolution of resistance to these compounds is a major threat to public health. 'Knockdown resistance' to pyrethroids (kdr) is frequently caused by nonsynonymous mutations in the voltage-gated sodium channel transmembrane protein (para) that reduce pyrethroid binding. Early detection of kdr is critical to the development of resistance management strategies in mosquitoes including Aedes aegypti, the most prevalent vector of dengue and yellow fever viruses. Brengues et al. described seven novel mutations in hydrophobic segment 6 of domain II of para in Ae. aegypti. Assays on larvae from strains bearing these mutations indicated reduced nerve sensitivity to permethrin inhibition. Two of these occurred in codons Iso1011 and Val1016 in exons 20 and 21 respectively. A transition in the third position of Iso1011 encoded a Met1011 replacement and a transversion in the second position of Val1016 encoded a Gly1016 replacement. We have screened this same region in 1318 mosquitoes in 32 additional strains; 30 from throughout Latin America. While the Gly1016 allele was never detected in Latin America, we found two new mutations in these same codons. A transition in the first position of codon 1011 encodes a Val replacement while a transition in the first position of codon 1016 encodes an Iso replacement. We developed PCR assays for these four mutations that can be read either on an agarose gel or as a melting curve. Selection experiments, one with deltamethrin on a field strain from Santiago de Cuba and another with permethrin on a strain from Isla Mujeres, Mexico rapidly increased the frequency of the Iso1016 allele. Bioassays of F(3) offspring arising from permethrin susceptible Val1016 homozygous parents and permethrin resistant Iso1016 homozygous parents show that Iso1016 segregates as a recessive allele in conferring kdr. Analysis of segregation between alleles at the 1011 and 1016 codons in the F(3) showed a high rate of recombination even though the two codons are only separated by a ~250 bp intron. The tools and information presented provide a means for early detection and characterization of kdr that is critical to the development of strategies for resistance management.
312 citations
Cites methods from "Simplification of adult mosquito bi..."
...After establishment of an F1 population in the laboratory, F2 adults were exposed to 1.2 µg of permethrin in a bottle bioassay (Brogdon & McAllister, 1998)....
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...F3 offspring were exposed to 1.2 µg of permethrin in a bottle bioassay (Brogdon & McAllister, 1998)....
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TL;DR: It is speculated that use of impregnated nets selected for higher oxidase and esterase levels in An.
Abstract: The permethrin tolerance (PT) of a population of the mosquito Anopheles gambiae (Diptera: Culicidae) increased following the introduction of permethrin-impregnated nets for malaria control in certain villages near Kisumu, western Kenya. Using a biochemical test that indirectly measures oxidases associated with permethrin resistance, we found that this population had higher oxidase levels than a comparison population from villages without impregnated nets. Mosquitoes from a colony of An. gambiae selected for PT, the RSP (reduced susceptibility to permethrin) strain, were exposed to permethrin with or without the oxidase inhibitor piperonyl butoxide (PB). Significantly higher mortality rates occurred when permethrin was synergized by PB, presumably by suppression of oxidases responsible for PT. An unselected (UNS) colony of An. gambiae that was more susceptible than RSP in a permethrin-susceptibility bioassay (i.e. LT50 22 min for UNS, vs. 42min for RSP) was compared with the RSP colony for levels of oxidases and esterases. The levels of both enzymes were very significantly higher in the RSP strain (P<0.0001). We speculate that use of impregnated nets selected for higher oxidase and esterase levels in An. gambiae to metabolize permethrin acquired from the nets. Both oxidase and esterase mechanisms could confer cross-resistance to other pyrethroids.
242 citations
TL;DR: The mechanisms of insecticide resistance, as well as specific instances of resistance emergence worldwide, are described, and prospects for resistance management and priorities for detection and surveillance are discussed.
Abstract: Insecticide resistance has been a problem in all insect groups that serve as vectors of emerging diseases. Although mechanisms by which insecticides become less effective are similar across all vector taxa, each resistance problem is potentially unique and may involve a complex pattern of resistance foci. The main defense against resistance is close surveillance of the susceptibility of vector populations. We describe the mechanisms of insecticide resistance, as well as specific instances of resistance emergence worldwide, and discuss prospects for resistance management and priorities for detection and surveillance.
240 citations
References
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TL;DR: Some general considerations show that the LD50, a standard measure for resistance monitoring, is very inefficient compared with diagnostic tests that accurately distinguish between resistant and susceptible individuals.
Abstract: Monitoring is critical to resistance management, but there has been very little discussion in the literature about the statistical design of monitoring programs. Some general considerations show that the LD50, a standard measure for resistance monitoring, is very inefficient compared with diagnostic tests that accurately distinguish between resistant and susceptible individuals. Even with diagnostic doses, sample sizes at any given location must often be very large (on the order of hundreds of individuals per population) to reliably detect resistance when it is present at frequencies of <10%. For those species where it is difficult to collect large numbers of individuals, resistance detection may not be a practical component of resistance management.
282 citations
Journal Article•
TL;DR: A simple, rapid, microplate-based assay that indirectly measures the differences in oxidase levels between individual susceptible, resistant, or induced mosquitoes is described.
Abstract: Optimum conditions are described for a simple, rapid, microplate-based assay that indirectly measures the differences in oxidase levels between individual susceptible, resistant, or induced mosquitoes. A small proportion (0.01-0.1) of a single mosquito is used, allowing multiple replicates of the oxidase assay. Cytochrome C is used as a positive control. The levels of oxidase found in sample populations of pyrethroid-susceptible, pyrethroid-resistant, and phenobarbital-induced Anopheles albimanus mosquitoes are characterized with the assay.
228 citations
TL;DR: A microtiter plate spectrophotometric system has been used together with the Bradford, Ellman, and van Asperen assays to measure protein concentration and the activities of acetylcholinesterase and carboxylesterase in small samples such as high-performance liquid chromatographic eluate fractions.
122 citations
TL;DR: As a guide to experimental design for bioassays, the effects of total sample size and dose selection on the precision of LD50 and LD90 estimates were determined by Monte Carlo simulations with the logit model, finding a sample size of 120 appears to be the minimum necessary for reliable estimation.
Abstract: As a guide to experimental design for bioassays, the effects of total sample size and dose selection on the precision of LD50 and LD90 estimates were determined by Monte Carlo simulations with the logit model. A sample size of 120 appears to be the minimum necessary for reliable estimation. For increased precision, sample sizes of 240 or more are required. A computer procedure was used to search for the percentage of mortality resulting in minimum predicted 95% confidence interval lengths for the LD50 and LD90 in dose-response experiments with three to eight doses, equal numbers of test subjects at each dose, and total sample sizes of 120, 240, 480, and 720. Regardless of the number of doses, the most precise LD50 estimates were obtained when responses when evenly distributed between 25 and 75%. Precise LD90 estimates, however, required one or two responses ≤10% and the majority between 75 and 95%.
105 citations