Table 2. Susceptibility of the selected fall armyworm strain to the Cry1Fa protein from B. thuringiensis.
| Response variable | Insect strain | Slope ± SE | LC50 or EC50 (95% CL)a | Resistance ratio (95% CL)b | χ2 | P |
|---|---|---|---|---|---|---|
| Mortality | Bahia-Bt | ncc | >30000 | >12 | nc | nc |
| Bahia-Cv | 0.86 ± 0.08 | 2361 (1600–3792) | 1 | 4.9 | 0.42 | |
| Growth inhibition | Bahia-Bt | 2.84 ± 0.24 | 22407 (17200–32346) | 549.3 (324.0–931.3) | 0.5 | 0.99 |
| Bahia-Cv | 0.93 ± 0.09 | 40.8 (24.9–60.4) | 1 | 1.3 | 0.93 |
The protein was applied superficially onto the artificial diet and mortality and growth inhibition were recorded after seven days of exposure.
The number of insects tested in the bioassays was 251 and 506 for the Bahia-Bt and Bahia-Cv, respectively.
aConcentration killing 50% (LC50) or causing 50% growth inhibition (EC50), with 95% confidence intervals in parentheses42; units are in nanograms toxin per cm2 diet.
bResistance ratio, the LC50 or EC50 value for the Bahia-Bt strain divided by the LC50 or EC50 values for the Bahia-Cv strain, with 95% confidence intervals in parentheses42.
cnc, not calculated, because of insufficient response even in the highest concentration tested (30,000 ng/cm2).