Applied and Environmental Microbiology (1995) 61, 2086-2092

W.J. Moar, M. Pusztai-Carey, H. Van Faassen, D. Bosch, R. Frutos, C. Rang, K. Luo and M.J. Adang (1995)
Development of Bacillus thuringiensis CryIC resistance by Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae)
Applied and Environmental Microbiology 61 (6), 2086-2092
Abstract: Selection of resistance in Spodoptera exigua (Hubner) to an HD-1 spore-crystal mixture, CryIC (HD-133) inclusion bodies, and trypsinized toxin from Bacillus thuringiensis subsp. aizawai and B. thuringiensis subsp. entomocidus was attempted by using laboratory bioassays. No resistance to the HD-1 spore-crystal mixture could be achieved after 20 generations of selection. Significant levels of resistance (11-fold) to CryIC inclusion bodies expressed in Escherichia coli were observed after seven generations. Subsequent selection of the CryIC-resistant population with trypsinized CryIC toxin resulted, after 21 generations of CryIC selection, in a population of S. exigua that exhibited only 8% mortality at the highest toxin concentration tested (320 µg/g), whereas the 50% lethal concentration was 4.30 µg/g for the susceptible colony. Insects resistant to CryIC toxin from HD-133 also were resistant to trypsinized CryIA(b), CryIC from B. thuringiensis subsp. entomocidus, CryIE-CryIC fusion protein (G27), CryIH, and CryIIA. In vitro binding experiments with brush border membrane vesicles showed a twofold decrease in maximum CryIC binding, a fivefold difference in K_d, and no difference in the concentration of binding sites for the CryIC-resistant insects compared with those for the susceptible insects. Resistance to CryIC was significantly reduced by the addition of HD-1 spores. Resistance to the CryIC toxin was still observed 12 generations after CryIC selection was removed. These results suggest that, in S. exigua, resistance to a single protein is more likely to occur than resistance to spore-crystal mixtures and that once resistance occurs, insects will be resistant to many other Cry proteins. These results have important implications for devising S. exigua resistance management strategies in the field.
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Database assignments for author(s): Michael J. Adang, William J. Moar

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Spodoptera exigua
Bacillus thuringiensis var. aizawai (entomopathogen)	Spodoptera exigua
Bacillus thuringiensis Cry1C-toxin (entomopathogen)	Spodoptera exigua
Bacillus thuringiensis var. entomocidus (entomopathogen)	Spodoptera exigua