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Identifier

000382275

Title

Διερεύνηση των μηχανισμών ανθεκτικότητας στα εντομοκτόνα και της διασποράς των υπεύθυνων γονιδίων σε πληθυσμούς των Bemisia Tabaci (αλευρώδη) και Tetranychus Urticae (τετράνυχου)

Alternative Title

Investigation of insecticide resistance mechanisms and geographical distribution of responsible genes in the whitefly Bemisia Tabaci and the spider mite Tetranychus Urticae

Author

Ηλίας, Άρης

Thesis advisor

Βόντας, Ιωάννης

Abstract

Spider mite Tetranychus urticae and whitefly Bemisia tabaci are two of the most damaging pests in agriculture. Chemicals are the main way to control their populations. However, their extensive use is responsible for the selection of extremely high levels of insecticide/acaricide resistance for both species. We examined the levels of resistance in nine T. urticae populations from Greece against a range of chemicals with different mode of actions. The majority of the populations displayed high levels of resistance in at least one active ingredient. In one population originating from a roses greenhouse we detected extremely high levels of resistance to abamectin. We examined the molecular mechanisms responsible for abamectin resistance, by employing a comprehensive approach including bioassays with synergists, biochemical analysis of detoxification pathways, use of RNAi via feedings with artificial diet, and molecular analysis of target sites. We identified a novel mutation in the GluCl3 which was strongly correlated with resistance. We employed genetic crosses and single individual genotyping to investigate the link between the mutation and the resistant phenotype, and concluded that the mutation has a crucial role in abamectin resistance and is necessary for the mite to survive at high concentrations of the chemical. Subsequently, molecular diagnostics were developed for the detection of abamectin resistance in the field. Ten populations of the whitefly Bemisia tabaci collected from Crete, exhibited resistance against different neonicotinoid insecticides. Laboratory selection with the neonicotinoids, imidacloprid and acetamiprid, was subsequently undertaken. The resistant strains exhibited very high levels of resistance to thiacloprid (RR>900) and moderate levels to imidacloprid (24 <RR< 56) and acetamiprid (9 <RR< 17). In vivo experiments with synergists as well as biochemical assays with model substrates and RNAi via feeding with artificial diet were used to investigate the underlying mechanisms. The involvement of cytochrome P450 detoxification in resistance was indicated. Real Time PCR showed higher expression levels of the known neonicotinoid metaboliser CYP6CM1 in the resistant strains. However, this specific P450 has been strongly associated with resistance to imidacloprid and thiacloprid but not to acetamiprid, and thus the existence of additional mechanism associated with neonicotinoid resistance is possible. In the last chapter of this thesis, we examined the presence and distribution of known target site resistance mutations in 33 T. urticae collections from 20 countries by sequencing. Those mutations were detected in variable frequencies and most of them had a wide distribution all over the world. We subsequently looked at the evolutionary history of the resistant acetylcholinesterase (ace) alleles, looking at whether the resistance mutations arose in one location and spread globally or in different locations independently. The genetic background of these mutations was examined by sequencing coding and non coding regions. Significant levels of genetic variation were observed, however there was no correlation with their geographical region. Taking into account the number of different mutations or combination of mutations and the fact that each mutation is associated with different genetic backgrounds we concluded that mutations arose in different geographic locations independently, at least three times.

Language

Greek

Subject

Acaricides

Acetylcholinesterase

Detoxification enzymes

Target site resistance

Ένζυμα αποτοξικοποίησης

Ακαρεοκτόνα

Ακετυλοχολινεστέραση

Μεταλλαγές ανθεκτικότητας

Issue date