Table 2.
Effect of antibiotics on rate of mortality by B. thuringiensis (Bt) and Enterobacter sp. NAB3 (EntB) on six Lepidoptera species.
| LT25 (95% FL) a | LT50 (95% FL) | ||||
| Species | Bacterial treatment | No antibiotics | Antibiotics | No antibiotics | Antibiotics |
| Vanessa cardui | untreated | no toxicity | no toxicity | no toxicity | no toxicity |
| Enterobacter | no toxicity | NAb | no toxicity | NA | |
| Bt DiPel 25 IU | 1.80 (1.54–2.26) | 13.20 (7.83 – >100)* | 1.91 (0.83–2.25) | 29.48 (12.44 – >100)* | |
| Bt DiPel 25 IU + EntB | NA | 1.62 (1.24–1.95)# | NA | 2.61 (2.21–2.97)# | |
| Manduca sexta | untreated | no toxicity | no toxicity | no toxicity | no toxicity |
| Enterobacter | no toxicity | NA | no toxicity | NA | |
| Bt DiPel 25 IU | 1.89 (1.48–2.23) | no toxicity | 3.04 (2.63–3.44) | no toxicity | |
| Bt DiPel 25 IU + EntB | NA | 3.81 (3.24–4.31) | NA | 5.95 (5.23–7.16) | |
| Pieris rapae | untreated | 10.34 (7.36–806.32) | no toxicity | 16.62 (9.67–>100) | No toxicity |
| Enterobacter | 6.91 (5.21–14.02) | no toxicity | 16.57 (9.79–96.47) | no toxicity | |
| Bt DiPel 25 IU | 1.26 (1.02–1.47) | 12.95 (7.83–>100)* | 1.76 (1.52–1.99) | 27.38 (12.04–>100)* | |
| Bt DiPel 25 IU + EntB | 1.98 (1.66–2.27)# | 1.47 (1.23–1.67)# | 2.84 (2.52–3.16)# | 1.98 (1.75–2.20)# | |
| Heliothis virescens | untreated | no toxicity | NA | no toxicity | NA |
| Enterobacter | no toxicity | NA | no toxicity | NA | |
| Bt DiPel 100 IU | 0.48 (0.17–0.80) | 8.62 (7.00–48.23)* | 1.13 (0.80–1.77) | 11.82 (8.48–267)* | |
| Bt DiPel 100 IU + EntB | NA | no toxicity | NA | no toxicity | |
| Pectinophora gossypiella | untreated | no toxicity | no toxicity | no toxicity | no toxicity |
| Enterobacter | no toxicity | no toxicity | no toxicity | no toxicity | |
| Bt MVPII 10 μg | 17.87 (15.48–20.22) | 15.46 (13.44–16.68) | 20.99 (18.94–29.59) | 17.56 (16.21–19.20) | |
| Bt MVPII 10 μg + EntB | 7.11 (3.61–9.44)# | 6.30 (2.78–8.62)# | 13.71 (10.52–20.13) | 12.61 (9.42–18.18) | |
| Lymantria dispar | untreated | 15.16 (8.90–398.16) | no toxicity | 40.09 (16.05–>100) | no toxicity |
| Enterobacter | no toxicity | no toxicity | no toxicity | no toxicity | |
| Bt MVPII 10 μg | 4.97 (4.28–5.68) | 9.52 (7.99–34.42)* | 8.17 (6.95–9.41) | 12.41 (10.40–125.70)* | |
| Bt MVPII 10 μg + EntB | NA | 5.23 (4.62–5.81)# | NA | 7.62 (6.76–9.24)# | |
Larval mortality rates were analyzed by PROC PROBIT. Estimates of the time (day) at which 25% and 50% of larvae died for each treatment are listed. Treatments with no significant mortality (X2 > 0.05) are defined as having no toxicity. A cut-off of > 100 was assigned to upper FL estimates (note: these are computational outputs, not actual estimates of larval lifespan). Bt mortality rates denoted with * are significantly different (non-overlapping fiducial limits (FL)) with their respective antibiotic treatment. Values denoted with # are significantly different with the addition of Enterobacter sp. NAB3, as compared with Bt alone. a Units are days, b NA = Not tested