Characterisation of insecticide resistance in Plutella xylostella (the diamondback moth)

Mishra, Ruchir (2011) Characterisation of insecticide resistance in Plutella xylostella (the diamondback moth). Doctoral thesis (DPhil), University of Sussex.

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Cry toxins are δ- endotoxins produced by Bacillus thuringiensis. They are toxic against different insect orders and are highly specific. However some of the insects have developed resistance to Cry toxins. Resistance to Cry1Ac in Heliothis virescens, Pectinophora gossypiella and Helicoverpa armigera has been linked to mutations in the cadherin gene. Plutella xylostella has also developed resistance to Cry1Ac but resistance to Cry1Ac in Plutella xylostella has not been linked to the cadherin gene. Previous studies have shown that a modified Cry1Ac toxin lacking helix-α1 of domain I is effective against insects which have developed resistance due to mutations in their cadherin gene. So it was decided to make modified Cry1Ac toxin lacking helix-α1 of domain I and check its effectiveness against the Cry1Ac resistant NOQA strain of Plutella xylostella. A modified cry1Ac toxin gene was created and expressed in E.coli. Bioassays conducted on the NOQA strain with modified and non-modified Cry1Ac showed that modified Cry1Ac was in fact the less effective toxin. This supports the hypothesis that the mechanism of resistance in NOQA population is not cadherin based.

A previous study has shown that field based resistance to spinosad in a Plutella xylostella strain collected from Pearl City, Hawaii is due to a point mutation in the ninth intron splice junction of nAChR Pxα6. Hence it was decided to check whether or not other spinosad resistant lepidopteran insects have similar mechanisms of resistance (i.e. splice-site mutation) as this population. PCR was performed to amplify nAChR intron 9 (including the splice junction) from a spinosad resistant Spodoptera litura population collected from the fields of Pakistan, but we were unable to amplify this region. Unfortunately the Spodoptera litura population was lost, so we could not carry on the experiments further. It was also decided to check whether Plutella xylostella NOQA population has the same splice site mutation as Plutella xylostella Pearl City population. Whether NOQA population is resistant to spinosad is not known. Sequencing showed that there was no splice site mutation present in NOQA.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Biochemistry
Subjects: Q Science > QD Chemistry > QD0241 Organic chemistry > QD0415 Biochemistry
Depositing User: Library Cataloguing
Date Deposited: 12 Aug 2011 09:00
Last Modified: 17 Aug 2015 13:51

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