Monitoring insecticide resistance development in beet army worm, Spodoptera exigua (Hiibner) (Lepidoptera: noctuidae)
2000
Abdullah, Md. | Ouab Sarnthoy | Siripan Tantakom | Somchai Isichaikul | Sudawan Chaeychomsri (Kasetsart Univ., Bangkok (Thailand). Faculty of Agriculture. Dept. of Entomology)
Field collected larvae of beet armyworm, Spodoptera exigua (Hiibner) were reared and evaluated for resistance against cypermethrin 10 EC, neem extract (Azadirachtin 0.1 percent) and Bacillus thuringiensis Berliner var. kurstaki (53,000 SU per mg) for 12 generations under laboratory condition by using leaf dip bioassay. Cypermethrin showed LC50 value of 251 ppm at F1 generation and decreased gradually to onward generations resulting LC50 value of 90 ppm at F12 generation for non-selection, whereas LC50 increased rapidly with a value of 8625 ppm at F12 generation under selection pressure. Neem extract exhibited LC50 value ranging from 3.98 ppm to 9.99 ppm for non-selection, whereas under selection pressure LC50 ranged from 4.38 ppm to 13.04 ppm throughout the generations. Bacillus thuringiensis var. kurstaki showed LC50 value which ranged from 7.3*10*[6) SU/L to 15.9*10*[6) SU/L for non-selection, and selection for resistance monitoring gave LC50 value ranged from 7.6*10*[6) SU/L to 73.9*10*[6) SU/L. Compared with non-selection strain, selection strain exhibited 95.83-fold, 1.44-fold and 5.6-fold increase in the LC50 for 12 generations against cypermethrin, neem extract and Bacillus thuringiensis var. kurstaki, respectively.
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