Why does pesticide resistance arise in mosquito populations

Furthermore, abdomen positive mosquitoes cannot all be assumed to become infective sporozoite-transmitters, particularly if vector life-span is reduced; a positive abdomen can also reflect a recent feed on an infected individual or the passage of sporozoites to the salivary glands. Finally, manual parity dissections have a number of known constraints, including insensitivity, especially in low endemicity areas, and inter-operator subjectivity. While every effort was made to consistently bisect individuals, and our reported sporozoite rate was low, other studies have demonstrated higher number of sporozoite false positives by PCR when abdomens were removed posterior to the junction of the abdomen and thorax We also cannot entirely discount natural variation in parity, which may have increased over the sampling period at the beginning of the rainy season.

These findings present a comprehensive overview of the current levels of insecticide resistance and underlying target site mutations present in Maferinyah, Guinea, an area of high malaria transmission.

Local mosquito populations were intensely resistant to pyrethroids alpha-cypermethrin, deltamethrin and permethrin , associated with high frequencies of the LF kdr allele. NY and IT mutations in the VGSC gene were present at lower levels and may warrant increased surveillance efforts, particularly as LF kdr approaches fixation. Restoration of mosquito susceptibility following pre-exposure to PBO indicates increased activity of detoxification enzymes is also contributing to pyrethroid resistance in this area and requires additional characterization.

Despite no ongoing vector control activities using carbamates, bendiocarb resistance was observed, and the GS Ace-1 allele was detected in a subset of tolerant individuals. Malaria infection was not associated with pyrethroid resistance but it was associated with bendiocarb resistance.

In general, resistant vectors were younger than their susceptible counterparts. Further studies are necessary to investigate the impact of insecticide resistance on vector fitness, including mosquito fecundity, egg viability, hatchability and parasite development following an infected blood meal.

Deltamethrin-treated LLINs had been distributed as part of a national mass campaign in Maferinyah in Sampling was conducted between 22 nd June and 17 th July , coinciding with the beginning of the long rainy season. All bioassays were performed using mosquitoes identified morphologically as An. Centers for Disease Control and Prevention CDC resistance intensity bioassays for three pyrethroid insecticides alpha-cypermethrin, deltamethrin and permethrin were conducted according to published guidelines Stock solutions of 1, 2, 5 and 10 times the diagnostic dose of insecticide alpha-cypermethrin: Bioassays for bendiocarb were conducted using the diagnostic dose 1X: Following coating, bottles were left to dry in a dark box.

Approximately 15—25 field-caught adult female An. In each bioassay, a control bottle, coated with acetone, was run in parallel. Ovarian dissection to determine mosquito parity was performed on ten mosquitoes including both survivors and those that died selected randomly from each bottle after bioassay completion The ovaries of each mosquito were dissected on a sterile microscope slide in distilled water, using a binocular dissection microscope and physiological status was determined.

The ovaries were then examined under a light microscope 10X magnification for the presence of tightly coiled skeins or loose coils, indicative of a nulliparous or parous ovary, respectively. A subset of susceptible and resistant An.

Positive controls from gDNA extracted from known An. Sub-samples of individuals from each district confirmed as An. At CDC, An. Amplified PCR products were visualized on 1. Detection of the LF West African kdr mutation was performed on a subset of individuals from all six districts according to the adapted protocol for allele-specific PCR developed by Martinez-Torres et al. Sequences were assembled manually in BioEdit v7. The presence of the GS Ace-1 mutation was determined using PCR restriction fragment length polymorphism analysis Presence of all three product sizes indicated that the sample was heterozygous.

Positive controls from gDNA extracted from a cultured P. PCR reactions were prepared using 6. Where molecular species ID data were available, results are reported for An. Other analyses utilized quasi-Poisson regression to estimate prevalence ratios PRs of mosquito survival, except the model in Fig. Outcomes from pyrethroid bioassays were evaluated separately to carbamate assays, unless otherwise specified. All statistical analyses were performed in R version 3.

Prior to study initiation, community consent was sought from village leaders and written, informed consent was obtained from the heads of all households selected for participation and from all fieldworkers who performed HLCs. Fieldworkers participating in human landing catches were provided with doxycycline malaria prophylaxis for the duration of the study.

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BMC Genomics 16 , Eventually, when many individuals in a population carry the resistance mutation, the chemical becomes ineffective. This can happen where insecticide "fogging" is common practice. Overseas, fogging is sometimes undertaken across entire neighbourhoods, several times a month, despite concerns about its effectiveness as well as its environmental and health impacts. Once resistance develops, it can spread to non-resistant mosquito populations in other areas.

Pest species, including mosquitoes, are often highly mobile because they fly or are carried passively in vehicles, ships and planes at any stage of their life cycle. Their mobility means mutations spread quickly, crossing borders and possibly seas. Despite this, Australian populations of Aedes mosquitoes remain susceptible to pyrethroids. Aedes aegypti the yellow fever mosquito is the main disease-carrying mosquito in Australia. Its population is restricted to urban areas of northern Queensland, where dengue can occur.

Recent research found that all Australian populations of this species are still vulnerable to pyrethroids. None of the hundreds of mosquitoes tested had any mutations in the sodium channel gene, despite the high incidence of such mutations in mosquito populations of South-East Asia. We believe these mosquitoes remain vulnerable to pyrethroids because in Australia pressure to select for resistance has been low.

Australia does not carry out routine fogging. If dengue is detected in an area , pyrethoids are used in highly regimented and limited fashion. Spraying is restricted to the insides of premises within selected house blocks, and then only for a short period. Importantly, water-filled artificial containers, which can serve as a habitat for larvae, are treated with insect growth regulators, which do not select for the pyrethroid resistance mutations.

With chemical resistance growing around the world, it is more urgent than ever that we co-ordinate action to control and reduce risk of resistance. Unfortunately, no global guidelines exist to minimise the evolution of resistance in mosquitoes. Adopting pesticide resistance management strategies has proven to be effective against other pests — for example, the corn earworm Helicoverpa armigera.

Guidelines include rotating different class of pesticides to deny pests the chance to develop resistance, and investing in non-chemical options such as natural predators of target pests. Resistance management strategies are particularly critical for new pesticides that have different modes of attack , such as preventing juvenile insects from moulting, or attacking various chemical receptors. To prolong the effectiveness of pesticides, we must develop these strategies before resistance begins to develop.

North Queensland may be an example to the rest of the world on the best path forward. Explore further. This article was originally published on The Conversation. Read the original article. Use this form if you have come across a typo, inaccuracy or would like to send an edit request for the content on this page. For general inquiries, please use our contact form. For general feedback, use the public comments section below please adhere to guidelines. Your feedback is important to us. The technique, referred to as the CDC bottle bioassay, is simple, rapid, and economical compared with alternatives.

The results can help guide the choice of insecticide used for spraying. Kits include bottles, insecticide, and manual. CDC has determined bottle bioassay threshold times and diagnostic doses for several species of mosquitoes. Using the suggested bottle diagnostic dosages, the threshold times for various susceptible colonies are provided below. The CDC entomology laboratory uses these threshold times and amounts for their bottle bioassays. The concentrations and cut-off times can be used as a starting point for determining diagnostic doses and threshold times for additional species if susceptible colonies or populations are available.

Once developed, the test can be routinely used for insecticide resistance testing. Information for Aedes aegypti , Ae. Culex species mosquitoes are important vectors of other arboviruses such as West Nile virus, St.