Costs and benefits of multiple resistance to insecticides for Culex quinquefasciatus mosquitoes

<p>Abstract</p> <p>Background</p> <p>The evolutionary dynamics of xenobiotic resistance depends on how resistance mutations influence the fitness of their bearers, both in the presence and absence of xenobiotic selection pressure. In cases of multiple resistance, these dynamics will also depend on how individual resistance mutations interact with one another, and on the xenobiotics applied against them. We compared <it>Culex quinquefasciatus </it>mosquitoes harbouring two resistance alleles <it>ace-1</it>^{<it>R </it>}and <it>Kdr</it>^{<it>R </it>}(conferring resistance to carbamate and pyrethroid insecticides, respectively) to mosquitoes bearing only one of the alleles, or neither allele. Comparisons were made in environments where both, only one, or neither type of insecticide was present.</p> <p>Results</p> <p>Each resistance allele was associated with fitness costs (survival to adulthood) in an insecticide-free environment, with the costs of <it>ace-1</it>^{<it>R </it>}being greater than for <it>Kdr</it>^<it>R</it>. However, there was a notable interaction in that the costs of harbouring both alleles were significantly less than for harbouring <it>ace-1</it>^{<it>R </it>}alone. The two insecticides combined in an additive, synergistic and antagonistic manner depending on a mosquito's resistance status, but were not predictable based on the presence/absence of either, or both mutations.</p> <p>Conclusion</p> <p>Insecticide resistance mutations interacted to positively or negatively influence a mosquito's fitness, both in the presence or absence of insecticides. In particular, the presence of the <it>Kdr</it>^{<it>R </it>}mutation compensated for the costs of the <it>ace-1</it>^{<it>R </it>}mutation in an insecticide-free environment, suggesting the strength of selection in untreated areas would be less against mosquitoes resistant to both insecticides than for those resistant to carbamates alone. Additional interactions suggest the dynamics of resistance will be difficult to predict in populations where multiple resistance mutations are present or that are subject to treatment by different xenobiotics.</p

Experimental hut evaluation of bednets treated with an organophosphate (chlorpyrifos-methyl) or a pyrethroid (lambdacyhalothrin) alone and in combination against insecticide-resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes

BACKGROUND: Pyrethroid resistant mosquitoes are becoming increasingly common in parts of Africa. It is important to identify alternative insecticides which, if necessary, could be used to replace or supplement the pyrethroids for use on treated nets. Certain compounds of an earlier generation of insecticides, the organophosphates may have potential as net treatments. METHODS: Comparative studies of chlorpyrifos-methyl (CM), an organophosphate with low mammalian toxicity, and lambdacyhalothrin (L), a pyrethroid, were conducted in experimental huts in Côte d'Ivoire, West Africa. Anopheles gambiae and Culex quinquefasciatus mosquitoes from the area are resistant to pyrethroids and organophosphates (kdr and insensitive acetylcholinesterase Ace.1(R)). Several treatments and application rates on intact or holed nets were evaluated, including single treatments, mixtures, and differential wall/ceiling treatments. RESULTS AND CONCLUSION: All of the treatments were effective in reducing blood feeding from sleepers under the nets and in killing both species of mosquito, despite the presence of the kdr and Ace.1(R )genes at high frequency. In most cases, the effects of the various treatments did not differ significantly. Five washes of the nets in soap solution did not reduce the impact of the insecticides on A. gambiae mortality, but did lead to an increase in blood feeding. The three combinations performed no differently from the single insecticide treatments, but the low dose mixture performed encouragingly well indicating that such combinations might be used for controlling insecticide resistant mosquitoes. Mortality of mosquitoes that carried both Ace.1(R )and Ace.1(S )genes did not differ significantly from mosquitoes that carried only Ace.1(S )genes on any of the treated nets, indicating that the Ace.1(R )allele does not confer effective resistance to chlorpyrifos-methyl under the realistic conditions of an experimental hut

Dosage-dependent effects of permethrin-treated nets on the behaviour of Anopheles gambiae and the selection of pyrethroid resistance

BACKGROUND: The evolution and spread of pyrethroid resistance in Anopheles gambiae s.s, the major malaria vector in sub-Saharan Africa, is of great concern owing to the importance of pyrethroid-treated nets in the WHO global strategy for malaria control. The impact of kdr (the main pyrethroid-resistance mechanism) on the behaviour of An. gambiae is not well understood. The objective of this study was to determine whether high or low doses of permethrin differ in their resistance-selection effects. METHODS: The effect of permethrin treatment was assessed under laboratory conditions using the tunnel test technique against susceptible, heterozygous and homozygous genotypes. Experimental huts trials were then carried out in Benin to assess the level of personal protection conferred by nets treated with a variety of permethrin concentrations and their impact on the selection for kdr allele. RESULTS: Tunnel tests showed that nets treated with permethrin at 250 and 500 mg/m(2 )induced higher mortality and blood feeding reduction among susceptible and heterozygous (RS) females as compared to the lower concentration (100 mg/m(2)). The experimental hut trials showed that the best personal protection was achieved with the highest permethrin concentration (1,000 mg/m(2)). Mosquito genotyping revealed a non-linear relationship in the survival of kdr susceptible and resistant genotypes with permethrin dosage. Higher dosages (≥250 mg/m(2)) killed more efficiently the RS genotypes than did lower dosages (50 and 100 mg/m(2)). CONCLUSION: This study showed that nets treated with high permethrin concentrations provided better blood feeding prevention against pyrethroid-resistant An. gambiae than did lower concentrations. Permethrin-treated nets seem unlikely to select for pyrethroid resistance in areas where the kdr mutation is rare and present mainly in heterozygous form

Interakcje między neurotoksynami na poziomie układu nerwowego owadów

Interakcje między pyretroidami i karbaminianem oraz toksyną ATX II z jadu anemona morskiego Anemonia sulcata były badane z użyciem metody pojedynczej i podwójnej przegrody olejowej. Obserwowano czynność bioelektryczną synaps w ostatnim zwoju odwłokowym oraz izolowanego aksonu olbrzymiego z układu nerwowego karaczana Periplaneta americana. Wykazano: (1) synergizm między permetryną (pyretroidem I typu) i propoksurem (karbaminianem), (2) przyspieszenie działania deltametryny (pyretroidem II typu) w obecności toksyny ATX II oraz brak wpływu toksyny na efektywność permetryny.Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 dofinansowane zostało ze środków MNiSW w ramach działalności upowszechniającej naukę