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Title: Investigating the molecular mechanisms of insecticide resistance in the tomato leaf miner Tuta Absoluta
Author: Berger , Madeleine
ISNI:       0000 0004 6348 3695
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2016
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Tuta absoluta is an economically significant pest of tomatoes, which has undergone a rapid expansion in its range during the past six years. One of the main means of controlling this pest is through the use of chemical insecticides including pyrethroids and spinosad. However, their intensive use has led to the development of resistance. The aim of this PhD was to understand the mechanisms underlying resistance to pyrethroids and spinosad. The target site of pyrethroids, the sodium channel, was cloned and three known knockdown resistance mutations, L1014F, M918T and T929I were found. High-throughput diagnostic assays were developed and the prevalence of the three mutations was then assessed. All three mutations were found at high frequencies in populations across the range of T. absoluta. Additionally, a fourth novel mutation L925M was found in 14% of samples. Therefore, pyrethroids are unlikely to be effective at controlling T. absoluta. Bioassays were conducted to determine the sensitivity of five populations of T. absoluta to spinosad. One population, from an area where control failure using spinosad was reported in 2012, exhibited a high level of resistance after selection in the laboratory with spinosad. Synergist bioassays did not show enhanced activity/expression of P450s and esterases. The transcriptome of T. absoluta was sequenced and used, in combination with degenerate PCR, to identify the target site of spinosad, the nicotinic acetylcholine receptor (nAChR) a6 subunit. Analysis of Taa6 revealed that two mutually exclusive exons (3a and 3b) that encode loop D of the ligand binding domain are both absent in all transcripts from the selected strain. Additionally, QPCR showed that a6 is down regulated in both larvae and adults of the selected strain. Taken together this study has provided new data on the molecular basis of resistance of T. absoluta to pyrethroids and spinosad.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available