Susceptibility of a Field-Derived, Bacillus thuringiensis-Resistant Strain of Diamondback Moth to In Vitro-Activated Cry1Ac Toxin

DOI: 10.1128/AEM.67.9.4372-4373.2001

Article Figures & Data

Table 1.

Toxicity of crystalline Cry1Ac for ROTH, UNSEL, and Cry1Ac-SEL populations of P. xylostella

Strain	Form of toxin	LC₅₀ (95% FL)^a	Avg slope (SE)	RR^b
ROTH	Crystal^c	0.0020 (0.0001–0.0085)	0.69 (0.18)
	Spore-crystal^d	0.0013 (0.0003–0.0039)	0.85 (0.19)
	NAT spore-crystal^d,^e	0.0020 (0.0008–0.004)	2.12 (0.53)
UNSEL	Crystal	0.0880 (0.034–0.19)	1.29 (0.24)	44
	Spore-crystal	0.0920 (0.03–0.2)	1.23 (0.24)	71
	NAT spore-crystal	0.1110 (0.0003–0.315)	1.64 (0.61)	55
Cry1Ac-SEL	Crystal	2.33 (0.14–29.62)	0.54 (0.22)	1,170
	Spore-crystal	3.60 (1.1–15.0)	0.81 (0.24)	2,770
	NAT spore-crystal	2.08 (0.56–6.01)	0.64 (0.16)	1,040

↵a Expressed in micrograms per milliliter. At least 150 larvae (F₁₁) were used in each experiment. LC₅₀, 50% lethal concentration FL, fiducial limits.
↵b Resistance ratio of 50% lethal concentrations for the UNSEL and Cry1Ac-SEL populations to those for the ROTH population.
↵c Expressed in E. coli.
↵d Expressed in B. thuringiensisIPS78/11 and applied as a spore-crystal mixture.
↵e NAT, N-terminally activated toxin.

Table 2.

Toxicity of in vitro solubilized and activated Cry1Ac for ROTH, UNSEL, and Cry1Ac-SEL populations of P. xylostella

Strain	Form of toxin^c	LC₅₀ (95% FL)^a	Avg slope (SE)	RR^b
ROTH	Crystal	15 (8–64)	0.69 (0.18)
	Solubilized^d	10 (8–22)	1.11 (0.29)
	Activated^d	15 (15–45)	1.18 (0.39)
UNSEL	Crystal	660 (255–1425)	1.29 (0.24)	44
	Solubilized	3,150 (975–6300)	2.02 (0.43)	315
	Activated	375 (135–750)	1.99 (0.44)	25
Cry1Ac-SEL	Crystal	17,475 (1,050–222,150)	0.54 (0.22)	1,170
	Solubilized	>150,000	0.44 (0.15)	>15,000
	Activated	1,410 (465–3,150)	0.65 (0.14)	94

↵a Values are expressed as picomolar concentrations due to differences in mass between the protoxin and activated forms of Cry1Ac. At least 150 larvae (F₁₁) were used in each experiment. LC₅₀, 50% lethal concentration. FL, fiducial limits.
↵b Resistance ratio of 50% lethal concentrations for the UNSEL and Cry1Ac-SEL populations to those for the ROTH population.
↵c Expressed in E. coli.
↵d Solubilized in 50 mM Na₂CO₃ and, where indicated, activated with 1 mg of trypsin per ml.