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Resistance to Organophosphorus Insecticides in the predatory mite Ttphlodromus pyri Scheuten (Acarina:Phytoseiidae), an important biocontrol agent in apple orchards

Resistance to Organophosphorus Insecticides in the predatory mite Ttphlodromus pyri Scheuten (Acarina:Phytoseiidae), an important biocontrol agent in apple orchards
Resistance to Organophosphorus Insecticides in the predatory mite Ttphlodromus pyri Scheuten (Acarina:Phytoseiidae), an important biocontrol agent in apple orchards

Typhlodromus pyri collected from orchards in the W of England showed differences in the intensity and spectrum of resistance to several OPs in laboratory bioassays when compared with standard OP-resistant mites from the SE.

There were significant differences between strains of T. pyri for total development period, with the two OP-susceptible strains having the longest development times from egg to adult. There were significant differences in preoviposition time between strains but this was not correlated with resistance status. The East Malling OP-resistant strain produced significantly more eggs in total than the other strains, and the standard OP-susceptible significantly less. There were significant differences in dorsal shield size between strains.

In laboratory assays with an OP-resistant strain of T. pyri no differences were found in LC50s when the mites were treated with synergists for esterases, glutathione S-transferases and mixed function oxidases in conjunction with phosalone (an OP), compared to the LC50 obtained with phosalone alone. Spectrophotometric assays of esterase activity showed no differences in activity between OP-resistant and OP-susceptible mites. GST activity, while showing significant differences between strains was not well correlated with resistance to OPs.

Assays of acetylcholinesterase activity showed activity in the OP-resistant strains tested to be half that of the OP-susceptible mites and the enzyme was less inhibited by addition of an OP than the enzyme from OP-susceptible mites. These results indicated that an altered AChE is likely to be the major mechanism of resistance to OPs in the strains of T. pyri tested.

Degenerate primers were used in PCR to amplify part of the acetylcholinesterase gene in T. pyri and Drosophila spp. Sequence data obtained from Drosophila showed 100% homology with sequences recorded in the database. The sequence for T. pyri was not homologous with any sequence in the database, but a small section of the conceptually translated protein sequence was shown to be analogous to the AChE active site, confirming that this was part of the AChE gene.

University of Southampton
Fitzgerald, Jean Dorothy
Fitzgerald, Jean Dorothy

Fitzgerald, Jean Dorothy (1999) Resistance to Organophosphorus Insecticides in the predatory mite Ttphlodromus pyri Scheuten (Acarina:Phytoseiidae), an important biocontrol agent in apple orchards. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Typhlodromus pyri collected from orchards in the W of England showed differences in the intensity and spectrum of resistance to several OPs in laboratory bioassays when compared with standard OP-resistant mites from the SE.

There were significant differences between strains of T. pyri for total development period, with the two OP-susceptible strains having the longest development times from egg to adult. There were significant differences in preoviposition time between strains but this was not correlated with resistance status. The East Malling OP-resistant strain produced significantly more eggs in total than the other strains, and the standard OP-susceptible significantly less. There were significant differences in dorsal shield size between strains.

In laboratory assays with an OP-resistant strain of T. pyri no differences were found in LC50s when the mites were treated with synergists for esterases, glutathione S-transferases and mixed function oxidases in conjunction with phosalone (an OP), compared to the LC50 obtained with phosalone alone. Spectrophotometric assays of esterase activity showed no differences in activity between OP-resistant and OP-susceptible mites. GST activity, while showing significant differences between strains was not well correlated with resistance to OPs.

Assays of acetylcholinesterase activity showed activity in the OP-resistant strains tested to be half that of the OP-susceptible mites and the enzyme was less inhibited by addition of an OP than the enzyme from OP-susceptible mites. These results indicated that an altered AChE is likely to be the major mechanism of resistance to OPs in the strains of T. pyri tested.

Degenerate primers were used in PCR to amplify part of the acetylcholinesterase gene in T. pyri and Drosophila spp. Sequence data obtained from Drosophila showed 100% homology with sequences recorded in the database. The sequence for T. pyri was not homologous with any sequence in the database, but a small section of the conceptually translated protein sequence was shown to be analogous to the AChE active site, confirming that this was part of the AChE gene.

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Published date: 1999

Identifiers

Local EPrints ID: 463754
URI: http://eprints.soton.ac.uk/id/eprint/463754
PURE UUID: 226b851a-5ac7-4412-a227-de2ffafb4a94

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Date deposited: 04 Jul 2022 20:56
Last modified: 04 Jul 2022 20:56

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Author: Jean Dorothy Fitzgerald

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