Cross-resistance between a Bacillus thuringiensis Cry toxin and non-Bt insecticides in the diamondback moth.
BACKGROUND
Bacillus thuringiensis Berliner (Bt) crystal (Cry) toxins are expressed in various transgenic crops and are also used as sprays in integrated pest management and organic agricultural systems. The diamondback moth (Plutella xylostella L.) is a major worldwide pest of crucifer crops and one that has readily acquired field resistance to a broad range of insecticides.


RESULTS
Selection of a subpopulation of the P. xylostella SERD4 population with the pyrethroid deltamethrin increased resistance to both deltamethrin and Cry1Ac relative to an unselected subpopulation. Selection of a second subpopulation with the Bt toxin Cry1Ac also increased resistance to both Cry1Ac and deltamethrin. A complementation test between the Cry1Ac-selected and deltamethrin-selected subpopulations suggested the presence of a common genetic locus or loci that control resistance to both insecticides. A piperonyl butoxide analogue with potent inhibitory activity against insect esterases significantly increased the toxicity of Cry1Ac and deltamethrin against the respective resistant subpopulations, but showed no such synergism with the unselected subpopulation of SERD4.


CONCLUSIONS
Selection of one resistance phenotype resulted in the simultaneous selection of the other. This phenomenon could be due to a single mechanism acting against both classes of insecticide or to genetically linked, but separate, mechanisms.
Sayyed
Ali H
AH
School of Life Sciences, University of Sussex, Falmer, Brighton, East Sussex BN1 9QG, UK. h.a.sayyed@sussex.ac.uk
Moores
Graham
G
Crickmore
Neil
N
Wright
Denis J
DJ
D000818:Animals; D001413:Bacillus thuringiensis / Q000737:chemistry; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000494:pharmacology*; D003433:Crosses, Genetic; D004731:Endotoxins / Q000494:pharmacology*; D005260:Female; D005816:Genetic Complementation Test; D008040:Genetic Linkage; D006460:Hemolysin Proteins / Q000494:pharmacology*; D007305:Insecticide Resistance / Q000235:genetics; D007306:Insecticides / Q000494:pharmacology*; D008296:Malaysia; D008297:Male; D009036:Moths / Q000187:drug effects* / Q000235:genetics*; D009570:Nitriles / Q000494:pharmacology; D010572:Pest Control, Biological; D010641:Phenotype; D011722:Pyrethrins / Q000494:pharmacology; D012641:Selection, Genetic
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; C017180:decamethrin