Characterisation of neonicotinoid resistance in the cotton aphid, Aphis gossypii from Australian cotton

Langfield, Kate Louise

Characterisation of neonicotinoid resistance in the cotton aphid, Aphis gossypii from Australian cotton

Langfield, Kate Louise

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Publication Type:: Thesis
Issue Date:: 2017

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Field	Value	Language
dc.contributor.author	Langfield, Kate Louise
dc.date.accessioned	2017-09-13T00:49:29Z
dc.date.available	2017-09-13T00:49:29Z
dc.date.issued	2017
dc.identifier.uri	http://hdl.handle.net/10453/116898
dc.description	University of Technology Sydney. Faculty of Science.	en_AU
dc.description.abstract	The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a highly polyphagous pest that inflicts serious damage to a broad range of agricultural, horticultural and greenhouse crops. In Australia, A. gossypii is a significant pest of cotton and is difficult to control with insecticides because of its high propensity to develop resistance. Neonicotinoids are among the most effective insecticides used to control A. gossypii but the recent detection of resistance threatens their longevity. Consequently, I aimed to restore neonicotinoid efficacy against A. gossypii through elucidation of underlying resistance mechanism(s). Bioassay was used to measure thiamethoxam (neonicotinoid) response in three field strains collected from commercial cotton. Resistance ratios between 49- and 85-fold were produced and resistance was correlated with potential field control failures via a glasshouse efficacy trial. Results showed that resistant A. gossypii could complete their development on cotton grown from thiamethoxam-treated seed. A second trial investigated the use of phorate (an organophosphate) as an alternative pre-germination treatment to thiamethoxam. Phorate effectively controls neonicotinoid resistant A. gossypii but cross resistance between phorate and the carbamate insecticide pirimicarb must be carefully considered as part of any sustainable management strategy. PCR-Sequencing was employed to identify if mutation R81T known to confer resistance to neonicotinoid compounds was present in Australian A. gossypii. Comparative sequence analysis between susceptible and resistant strains confirmed the absence of mutation R81T. Potential biochemical mechanisms of thiamethoxam resistance in A. gossypii were then studied using synergist bioassays. The use of the synergist piperonyl butoxide in tandem with thiamethoxam completely or partially suppressed resistance. This suggests that resistance is at least in part, mediated by overexpression of detoxification enzymes that could subsequently be targeted to achieve improved field control of resistant aphids. High-throughput sequencing of the A. gossypii transcriptome found differences in gene expression associated with thiamethoxam resistance. Two transcripts involved in the detoxification of xenobiotics (putatively annotated as cytochrome P450 gene 6K1-like) were found differentially expressed between resistant and susceptible strains. Transcript expression was further validated by qRT-PCR and showed a similar tendency in up-regulation of expression. As such I identified this gene as the strongest candidate for thiamethoxam resistant A. gossypii. This study has generated a comprehensive transcriptome resource for A. gossypii that has characterised the expression of numerous important transcripts encoding proteins involved in insecticide resistance. Consequently, my study will contribute to future research relating to molecular characterization of insecticide resistance mechanisms in A. gossypii and other insect pests.	en_AU
dc.format	Thesis (PhD)
dc.language.iso	en_AU	en_AU
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/116898/2/02whole.pdf
dc.rights	au.edu.uts.lib/ppc
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	info:eu-repo/semantics/openAccess
dc.subject	Aphis gossypii Glover (Hemiptera: Aphididae)	lat
dc.subject	Pest of cotton.	en
dc.subject	Resistance.	en
dc.subject	Neonicotinoid efficacy.	en
dc.subject	Glasshouse efficacy trial.	en
dc.subject	Thiamethoxam-treated seed.	en
dc.subject	PCR-Sequencing.	en
dc.subject	Mutation R81T.	en
dc.subject	Cytochrome P450 gene 6K1-like.	en
dc.subject	Synergist bioassays.	en
dc.subject	Insecticide resistance.	en
dc.title	Characterisation of neonicotinoid resistance in the cotton aphid, Aphis gossypii from Australian cotton	en_AU
dc.type	Thesis	en_AU
utslib.copyright.status	open_access

Abstract:

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a highly polyphagous pest that inflicts serious damage to a broad range of agricultural, horticultural and greenhouse crops. In Australia, A. gossypii is a significant pest of cotton and is difficult to control with insecticides because of its high propensity to develop resistance. Neonicotinoids are among the most effective insecticides used to control A. gossypii but the recent detection of resistance threatens their longevity. Consequently, I aimed to restore neonicotinoid efficacy against A. gossypii through elucidation of underlying resistance mechanism(s). Bioassay was used to measure thiamethoxam (neonicotinoid) response in three field strains collected from commercial cotton. Resistance ratios between 49- and 85-fold were produced and resistance was correlated with potential field control failures via a glasshouse efficacy trial. Results showed that resistant A. gossypii could complete their development on cotton grown from thiamethoxam-treated seed. A second trial investigated the use of phorate (an organophosphate) as an alternative pre-germination treatment to thiamethoxam. Phorate effectively controls neonicotinoid resistant A. gossypii but cross resistance between phorate and the carbamate insecticide pirimicarb must be carefully considered as part of any sustainable management strategy. PCR-Sequencing was employed to identify if mutation R81T known to confer resistance to neonicotinoid compounds was present in Australian A. gossypii. Comparative sequence analysis between susceptible and resistant strains confirmed the absence of mutation R81T. Potential biochemical mechanisms of thiamethoxam resistance in A. gossypii were then studied using synergist bioassays. The use of the synergist piperonyl butoxide in tandem with thiamethoxam completely or partially suppressed resistance. This suggests that resistance is at least in part, mediated by overexpression of detoxification enzymes that could subsequently be targeted to achieve improved field control of resistant aphids. High-throughput sequencing of the A. gossypii transcriptome found differences in gene expression associated with thiamethoxam resistance. Two transcripts involved in the detoxification of xenobiotics (putatively annotated as cytochrome P450 gene 6K1-like) were found differentially expressed between resistant and susceptible strains. Transcript expression was further validated by qRT-PCR and showed a similar tendency in up-regulation of expression. As such I identified this gene as the strongest candidate for thiamethoxam resistant A. gossypii. This study has generated a comprehensive transcriptome resource for A. gossypii that has characterised the expression of numerous important transcripts encoding proteins involved in insecticide resistance. Consequently, my study will contribute to future research relating to molecular characterization of insecticide resistance mechanisms in A. gossypii and other insect pests.

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