BackgroundCabbage stem flea beetle (CSFB), Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae) is a major early season pest of oilseed rape throughout Europe. Pyrethroids have been used for controlling this pest by foliar application, but in recent years control failures have occurred, particularly in Germany due to the evolution of knock-down resistance (kdr). The purpose of this study was to investigate the incidence and spread of pyrethroid resistance in CSFB collected in Germany, Denmark and the United Kingdom during 2014. The level of pyrethroid resistance was measured in adult vial tests and linked to the presence of kdr genotypes.ResultsAlthough kdr (L1014F) genotypes are present in all three countries, marked differences in pyrethroid efficacy were found in adult vial tests. Whereas Danish CSFB samples were in general susceptible to recommended label rates, those collected in the UK mostly resist such rates to some extent. Moderately resistant and susceptible samples were found in Germany. Interestingly, some of the resistant samples from the UK did not carry the kdr allele, which is in contrast to German CSFB. Pre-treatment with PBO, prior to exposure to λ-cyhalothrin suggested involvement of metabolic resistance in UK samples.ConclusionDanish samples were mostly susceptible with very low resistance ratios, while most other samples showed reduced sensitivity in varying degrees. Likewise, there was a clear difference in the presence of the kdr mutation between the three countries. In the UK, the presence of kdr genotypes did not always correlate well with resistant phenotypes. This appears to be primarily conferred by a yet undisclosed, metabolic-based mechanism. Nevertheless our survey disclosed an alarming trend concerning the incidence and spread of CSFB resistance to pyrethroids, which is likely to have negative impacts on oilseed production in affected regions due to the lack of alternative modes of action for resistance management purposes.
The antipsychotic drug thioridazine is a candidate drug for an alternative treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) in combination with the β-lactam antibiotic oxacillin. The drug has been shown to have the capability to resensitize MRSA to oxacillin. We have previously shown that the expression of some resistance genes is abolished after treatment with thioridazine and oxacillin. To further understand the mechanism underlying the reversal of resistance, we tested the expression of genes involved in antibiotic resistance and cell wall biosynthesis in response to thioridazine in combination with oxacillin. We observed that the oxacillin-induced expression of genes belonging to the VraSR regulon is reduced by the addition of thioridazine. The exclusion of such key factors involved in cell wall biosynthesis will most likely lead to a weakened cell wall and affect the ability of the bacteria to sustain oxacillin treatment. Furthermore, we found that thioridazine itself reduces the expression level of selected virulence genes and that selected toxin genes are not induced by thioridazine. In the present study, we find indications that the mechanism underlying reversal of resistance by thioridazine relies on decreased expression of specific genes involved in cell wall biosynthesis.
The newly collected field strain 845b had significantly higher constitutive gene expression than both WHO-SRS and 791a. High constitutive expression of CYP4G2 in houseflies indicates a possible role of this gene in metabolic resistance. There is a strong indication that CYP6G4 is a major insecticide resistance gene involved in neonicotinoid resistance.
BackgroundSpinosad is important in pest management strategies of multiple insect pests. However, spinosad resistance is emerging in various pest species. Resistance has in some species been associated with alterations of the target-site receptor, but in others P450s seems to be involved. We test the possible importance of nine cytochrome P450 genes in the spinosad-resistant housefly strain 791spin and investigate the influence of spinosad on P450 expression in four other housefly strains.ResultsSignificant differences in P450 expression of the nine P450 genes in the four strains after spinosad treatment were identified in 40% of cases, most of these as induction. The highly expressed CYP4G2 was induced 6.6-fold in the insecticide susceptible WHO-SRS females, but decreased 2-fold in resistant 791spin males. CYP6G4 was constitutively higher expressed in the resistant strain compared to the susceptible strain. Furthermore, CYP6G4 gene expression was increased in susceptible WHO-SRS flies by spinosad while the expression level did not alter significantly in resistant fly strains. Expression of CYP6A1 and male CYP6D3 was constitutively higher in the resistant strain compared to the susceptible. However, in both cases male expression was higher than female expression.Conclusion CYP4G2, CYP6A1, CYP6D3 and CYP6G4 have expressions patterns approaching the expectations of a hypothesized sex specific spinosad resistance gene. CYP4G2 fit requirements of a spinosad resistance gene best, making it the most likely candidate. The overall high expression level of CYP4G2 throughout the strains also indicates importance of this gene. However, the data on 791spin are not conclusive concerning spinosad resistance and small contributions from multiple P450s with different enzymatic capabilities could be speculated to do the job in 791spin. Differential expression of P450s between sexes is more a rule than an exception. Noteworthy differences between spinosad influenced expression of P450 genes between a field population and established laboratory strains were shown.
BackgroundThe housefly is a global pest that has developed resistance to most insecticides applied against it. Resistance of the spinosad-resistant strain 791spin and the neonicotinoid-resistant 766b strain is believed to be due to metabolism. We investigate differentially expressed genes in these two resistant strains related to metabolism in comparison with an insecticide-susceptible reference strain.ResultsGenes involved in metabolism of xenobiotics were primarily up-regulated in resistant flies with some differences between resistant strains. The cyp4g98 and cyp6g4 genes proved interesting in terms of neonicotinoid resistance, while cyp4d9 was overexpressed in 791spin compared to spinosad-susceptible strains. GSTs, ESTs and UGTs were mostly overexpressed, but not to the same degree as P450s. We present a comprehensive and comparative picture of gene expression in three housefly strains differing significantly in their response to insecticides. High differential expression of P450s and genes coding for cuticle protein indicates a combination of factors involved in metabolic neonicotinoid and spinosad resistance.ConclusionResistance in these strains is apparently not linked to the alteration of a single gene but is composed of several changes including differential expression of genes encoding metabolic detoxification enzymes.
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