2 research outputs found
Molecular mechanisms of insecticide resistance in the glasshouse whitefly, Trialeurodes vaporariorum
The whitefly Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae) is a
serious pest of protected vegetable and ornamental crops in most temperate regions of
the world. Neonicotinoids, pymetrozine (a feeding blocker), spiromesifen (a tetronic
acid derivative), bifenthrin (a pyrethroid), and pyriproxyfen (a juvenile hormone
mimic) are among the most important insecticides used to control this species.
Bioassays were used to quantify responses of recently-collected strains of T.
vaporariorum to three neonicotinoids (imidacloprid, thiamethoxam, and acetamiprid),
pymetrozine, spiromesifen, bifenthrin, and pyriproxyfen. 454 pyrosequencing was
exploited to generate the first transcriptome for this species. PCR-sequencing was
used to identify mutations in the target proteins of spiromesifen and bifenthrin
potentially associated with resistance to these compounds. Microarray sequencing
technology was employed to investigate differences in gene expression associated
with pyriproxyfen resistance.
Resistance to neonicotinoids was age-specific in expression and consistently
associated with resistance to pymetrozine, supporting a hypothesis of metabolic
resistance analogous to that in the tobacco whitefly, Bemisia tabaci. Bioassays also
showed moderate to high level resistance to spiromesifen, bifenthrin and
pyriproxyfen in some strains. Analysis of the transcriptome identified genes encoding
enzymes involved in the detoxification of xenobiotics (cytochrome P450s,
carboxyl/cholinesterases, and glutathione-s transferases) and ones encoding
insecticide targets: acetyl-coA carboxylase (ACCase), the target of spiromesifen and
the voltage-gated sodium channel protein targeted by pyrethroids. PCR-sequencing
revealed a single nucleotide polymorphism in the ACCase gene, which was
consistently associated with spiromesifen resistance. Three amino-acid substitutions
in the sodium channel of pyrethroid-resistant T. vaporariorum were found in
positions previously implicated in pyrethroid resistance in B. tabaci. Microarray
sequencing disclosed that a cytochrome P450 gene (CYP4G61) was overexpressed in
a strain selected for increased pyriproxyfen resistance. The implications of these
results and opportunities for further work are discussed.BBSRCBayer CropScienc
Pyrosequencing the transcriptome of the greenhouse whitefly, Trialeurodes vaporariorum reveals multiple transcripts encoding insecticide targets and detoxifying enzymes.
Published onlineJournal ArticleResearch Support, Non-U.S. Gov'tBACKGROUND: The whitefly Trialeurodes vaporariorum is an economically important crop pest in temperate regions that has developed resistance to most classes of insecticides. However, the molecular mechanisms underlying resistance have not been characterised and, to date, progress has been hampered by a lack of nucleotide sequence data for this species. Here, we use pyrosequencing on the Roche 454-FLX platform to produce a substantial and annotated EST dataset. This 'unigene set' will form a critical reference point for quantitation of over-expressed messages via digital transcriptomics. RESULTS: Pyrosequencing produced around a million sequencing reads that assembled into 54,748 contigs, with an average length of 965 bp, representing a dramatic expansion of existing cDNA sequences available for T. vaporariorum (only 43 entries in GenBank at the time of this publication). BLAST searching of non-redundant databases returned 20,333 significant matches and those gene families potentially encoding gene products involved in insecticide resistance were manually curated and annotated. These include, enzymes potentially involved in the detoxification of xenobiotics and those encoding the targets of the major chemical classes of insecticides. A total of 57 P450s, 17 GSTs and 27 CCEs were identified along with 30 contigs encoding the target proteins of six different insecticide classes. CONCLUSION: Here, we have developed new transcriptomic resources for T. vaporariorum. These include a substantial and annotated EST dataset that will serve the community studying this important crop pest and will elucidate further the molecular mechanisms underlying insecticide resistance.CASE PhD studentship BBSRCBayer CropScienceRothamsted Researc