| Abstract |
Arthropod pests seriously threaten food security and human health, as they
attack agricultural crops and transmit various diseases. Their control has been
largely based on chemical insecticides. However the intense use of insecticides has
led in the development of resistance, mainly achieved by target site resistance
mutations and detoxification, enzymes, such as the Cytochrome P450s, the
Glutathione S-transferases GSTs and the Carboxylesterases (CCEs). The same
detoxification enzymes also participate in the adaptation of arthropod pests to their
hosts, as they also metabolize – inactivate phytotoxins. In this thesis, I used
transgenic approaches, bioassays, transcriptomics and biochemical/ functional
techniques to investigate detoxification mechanisms of major arthropod pests, such
as the Aedes aegypti, the Bactrocera oleae and the Tetranychus urticae, against
xenobiotics.
First, the A. aegypti cytochrome P450 CYP9J28 was successfully expressed in
Drosophila melanogaster and shown to confer significant levels of resistance in vivo,
providing solid evidence for its role in pyrethroid resistance and showing that ectopic
expression in D. melanogaster may be a robust approach for validation of candidate
resistance genes.
Second, a large transcriptomic dataset of B. oleae was generated and more
than 130 putative detoxification genes were identified and phylogenetically
classified. The transcriptome was used for the construction of a microarray tool,
which was used, in its pilot application, to study detoxification and adaptation
mechanisms of the olive fly against insecticides and olive flesh/phytotoxins,
respectively. The pyrethroid resistance study indicated the association of two
cytochrome P450 genes with the phenotype. Several detoxification and digestive
genes were found over-expressed upon development in olives (green versus black
versus artificial diet), providing a useful starting point for further investigation.
In the last chapter, my study dealt and focused on T. urticae GSTs that had
been associated with insecticide resistance by microarray studies. Four GSTs were
functionally expressed and characterized. TuGSTd14 was found to interact with abamectin, supporting earlier work that GSTs are may play a role in abamectin
resistance. Strong evidence were provided that TuGSTd05 catalyzes the conjugation
of glutathione (GSH) to cyflumetofen in vitro and the possible site of attack as well as
key amino acids possibly implicated in the interaction were identified. This study
represents the first functional convincing report for the implication of an acari GST in
resistance.
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Adaptation of arthropod pests in plant allelochemicals and pesticides, with emphasis on the role of detoxification
