Table 1.

Mean knockdown time (KT) in minutes for populations of adult Tribolium castaneum assayed as single beetles or as groups of 10 for knockdown of 50% or 100% of the group.

Population 1 & Resistance Status	FAO % Resist. 2	Single KT (± SE) 3,4,5			50% KT (± SE) 3,4,5			100% KT (± SE) 3,4,5
Susceptible
USDA Lab Susceptible	0	8.46	±	0.66 A,a	5.19	±	0.21 A,b	9.13	±	0.46 A,a
Excelsior Springs	0	10.82	±	1.04 A,a	6.13	±	0.48 A,a	17.05	±	3.01 AB,b
Calgary, Alberta	0	9.24	±	0.42 A,a	7.27	±	0.11 A,a	16.23	±	1.21 AB,b
Davis, Calif.	0	14.13	±	0.84 AB,a	9.16	±	0.84 AB,a	34.83	±	7.42 AB,b
Arbuckle, Calif.	0	14.37	±	1.35 AB,a	10.00	±	0.30 B,a	31.28	±	3.12 AB,b
Williams, Calif.	0	10.91	±	1.01 A,a	10.05	±	0.53 B,a	26.16	±	2.15 AB,b
Weak Resistance
Thailand	15	14.62	±	2.00 AB,a	7.89	±	0.29 AB,a	29.17	±	3.92 AB,b
Abilene, Kansas	39	16.14	±	1.21 AB,a	11.50	±	0.61 BC,a	37.30	±	3.84 AB,b
Russell, Kansas	41	16.82	±	1.38 AB,a	14.38	±	0.42 CD,a	62.78	±	9.12 BC,b
Strong Resistance
Minneapolis, Kansas	89	24.47	±	2.35 B,a	16.98	±	1.04 D,a	100.20	±	11.77 C,b
Mitchell, Kansas	93	19.32	±	1.54 AB,a	14.55	±	0.87 CD,a	172.15	±	24.72 D,b
Red Level, Alabama	100	52.70	±	1.54 AB,a	24.33	±	2.05 E,a	194.13	±	22.13 D,b

¹ Name/location of each population tested and its resistance status as per Cato et al. [8]. ² Percent of beetles in a population estimated to be phosphine-resistant determined in a recent FAO test [8]. ³ Replications per KT type as follows: Single (10), KT₅₀ (5), and KT₁₀₀ (5). ⁴ Means for KT results in a row followed by the same lower case letter, and those in a column followed by the same upper case letter, are not significantly different according to a Tukey HSD post hoc analysis, p < 0.05. ⁵ All differences were determined by a Two-Way ANOVA, F = 8.416, df = 22, 204, p < 0.01.