TABLE 3.
Logit regression analysis of insect mortality following 11 SfMNPV treatments including wild-type SfNIC, five pure genotypes, and five co-occluded genotype mixtures, in second-instar Spodoptera frugiperda following per os inoculationa
| Inoculum | LC50 (OB/ml) | 95% Confidence limits
|
Intercept + SE | Relative potency | P | Reference | |
|---|---|---|---|---|---|---|---|
| Low | High | ||||||
| Wild-type SfNIC | 5.47 × 104 | 3.82 × 104 | 7.84 × 104 | −6.734 + 0.2602 | 1 | This study | |
| Genotype A | 2.38 × 105 | 1.64 × 105 | 3.48 × 105 | −7.643 + 0.2785 | 0.23 | <0.001 | This study |
| Genotype B | 1.93 × 105 | 1.33 × 105 | 2.82 × 105 | −7.515 + 0.2752 | 0.28 | <0.001 | This study |
| Genotype C | This study | ||||||
| Genotype D | This study | ||||||
| Genotype F | 1.53 × 105 | 1.06 × 105 | 2.22 × 105 | −7.369 + 0.2731 | 0.36 | <0.001 | This study |
| Genotype G | 34 | ||||||
| Genotype H | 2.45 × 105 | 1.89 × 105 | 3.21 × 105 | −7.392 + 0.2000 | 0.22 | <0.001 | 34 |
| Genotype I | 1.66 × 105 | 1.29 × 105 | 2.15 × 105 | −7.160 + 0.1963 | 0.33 | <0.001 | 34 |
| 75% B + 25% A | 1.08 × 105 | 7.53 × 104 | 1.56 × 105 | −7.156 + 0.2679 | 0.51 | 0.014 | This study |
| 75% B + 25% D | 5.05 × 104 | 3.09 × 104 | 8.24 × 104 | −4.431 + 0.5141 | 1.09 | N.S. | This study |
| 75% B + 25% F | 2.33 × 105 | 1.59 × 105 | 3.41 × 105 | −7.630 + 0.2787 | 0.24 | <0.001 | This study |
| 75% A + 25% C | 2.18 × 105 | 1.50 × 105 | 3.18 × 105 | −7.588 + 0.2766 | 0.25 | <0.001 | This study |
| 75% F + 25% C | 1.69 × 105 | 1.17 × 105 | 2.45 × 105 | −7.432 + 0.2735 | 0.32 | <0.001 | This study |
Logit regression of number of responding insects against loge(virus concentration) given in terms of loge odds ratio: loge(p/q) = a + bx. Regressions were fitted in GLIM with a common slope of 0.6173+0.0216(standard error) for all the virus inocula except the B + D mixture, which was fitted separately with a slope of 0.4090+0.0467, and the variants described in a previous study(31), H and I, with a slope of 0.5813+0.034. A test for nonparallelism was not significant for those virus inocula (χ2 = 4.18, d.f. = 24, P > 0.05). P values were calculated by t test of the differences between regression intercepts compared to that of the wild-type SfNIC isolate. Relative potencies were calculated as the ratio of effective concentrations relative to SfNIC except in the case of the B + D mixture, for which this represents the ratio of LC50 values and is not significant (N.S.) based on overlap of 95% confidence limits (26). As such, relative potencies indicate the relative pathogenicity of each genotype or mixtures of genotypes compared with that of the wild-type isolate. All bioassays were performed in second-instar S. frugiperda (∼25 insects/concentration, three replicates) using the droplet feeding method. OBs containing co-occluded genotype mixtures were produced by injecting S. frugiperda with mixtures of occlusion-devired virions (B+A, B+D, B+F, A+C, and F+C) in a ratio of 3:1. The proportion of each genotype was confirmed by densitometric analysis from semiquantitative PCR amplification (Fig. 3).