Molecular mechanisms of insecticide resistance in the glasshouse whitefly, Trialeurodes vaporariorum
Karatolos, Nikolaos
Date: 18 October 2011
Thesis or dissertation
Publisher
University of Exeter
Degree Title
PhD in Biological Sciences
Abstract
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) ...
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.
Doctoral Theses
Doctoral College
Item views 0
Full item downloads 0