Table 2.
Relative toxicity of five insecticides to two strains of S. zeamais [i.e., the pyrethroids susceptible (SzSusc) and pyrethroid resistant (SzPyrSel) strains] and two strains of S. oryzae (i.e., SoPyrTol and SoPyrR).
| Insecticide | Sitophilus strains | No. of insects | LD50 (95% FI) mg a.i/kg of grains | LD95 (95% FI) mg a.i/kg of grains | RR50 (95% CL) | RRa50 (95% CL) | Χ 2 | P |
|---|---|---|---|---|---|---|---|---|
| Deltamethrin | SzSusc | 493 | 0.68 (0.5–0.9) | 1.6 (1.2–2.8) | * | * | 7.42 | 0.09 |
| SzPyrSel | (—) | (—) | (—) | (>2500) | (>2500) | (—) | (—) | |
| SoPyrTol | 490 | 25.95 (23.1–28.5) | 82.5 (69.3–106.7) | * | 37.6 (35.1–40.3) | 2.20 | 0.53 | |
| SoPyrR | 495 | 69.39 (64.2–76.0) | 201.8 (159.8–291.5) | 2.7 (2.4–2.9) | 101.0 (91.2–110.9) | 1.54 | 0.67 | |
| Lambda-Cyhalothrin | SzSusc | 526 | 0.71 (0.7–0.8) | 1.5 (1.3–1.7) | * | * | 4.31 | 0.23 |
| SzPyrSel | (—) | (—) | (—) | (—) | (—) | (—) | (—) | |
| SoPyrTol | 596 | 12.06 (10.1–13.9) | 54.4(45.3–69.1) | * | 16.9 (15.9–18.0) | 1.57 | 0.81 | |
| SoPyrR | 588 | 174.3 (146.1–219.6) | 1243.1(973.4–2259.0) | 14.5 (9.8–21.2) | 244.6 (167.5–357.3) | 4.46 | 0.61 | |
| Indoxacarb | SzSusc | 689 | 0.40 (0.3–0.5) | 5.2 (3.9–7.4) | * | * | 6.77 | 0.24 |
| SzPyrSel | 599 | 3.79 (3.1–4.5) | 15.3 (12.9–19.1) | 9.5 (7.8–11.5) | 9.5 (7.8–11.5) | 1.67 | 0.80 | |
| SoPyrTol | 496 | 3.05 (2.6–3.5) | 11.2 (9.3–14.2) | * | 7.6 (6.3–9.6) | 1.06 | 0.78 | |
| SoPyrR | 512 | 1.55 (1.2–1.9) | 14.2 (10.6–20.5) | 0.5 (0.5–0.6) | 3.9 (3.2–4.8) | 4.72 | 0.45 | |
| Imidacloprid | SzSusc | 617 | 1.21 (0.9–1.7) | 13.0 (6.6–41.9) | * | * | 3.82 | 0.43 |
| SzPyrSel | 496 | 0.83 (0.7–3.4) | 15.5 (9.60–18.3) | 0.7 (0.5–1.1) | 0.7 (0.5–1.1) | 5.63 | 0.13 | |
| SoPyrTol | 398 | 1.32 (0.2–5.2) | 14.2 (8.50–19.4) | * | 1.1 (0.17–2.3) | 1.40 | 0.49 | |
| SoPyrR | 450 | 1.54 (0.5–4.1) | 16.6 (11.2–25.1) | 1.2 (0.6–5.1) | 1.3 (0.27–2.1) | 1.34 | 0.85 | |
| Thiamethoxam | SzSusc | 497 | 0.68 (0.6–0.8) | 2.6 (2.1–3.7) | * | * | 2.79 | 0.43 |
| SzPyrSel | 404 | 1.46 (1.1–2.0) | 15.6 (8.4–41.9) | 2.2 (1.7–2.8) | 2.2 (1.7–2.8) | 2.21 | 0.33 | |
| SoPyrTol | 597 | 1.95 (1.5–2.9) | 25.3 (11.9–90.9) | * | 2.9 (1.9–4.2) | 4.10 | 0.39 | |
| SoPyrR | 449 | 0.94 (0.69–1.2) | 12.8 (7.3–38.2) | 0.48 (0.3–0.7) | 1.4 (1.1–1.7) | 3.12 | 0.53 | |
| Spinosad | SzSusc | 635 | 15.7 (14.5–16.9) | 37.3 (32.5–45.5) | * | * | 7.36 | 0.12 |
| SzPyrSel | 522 | 23.6 (21.2–27.3) | 80.2 (57.9–141.6) | 1.5 (1.2–1.8) | 1.5 (1.2–1.8) | 6.07 | 0.11 | |
| SoPyrTol | 499 | 17.2 (13.8–20.7) | 80.5 (64.6–107.5) | * | 1.1 (0.7–1.3) | 1.88 | 0.59 | |
| SoPyrR | 512 | 21.5 (19.3–26.6) | 76.1 (69.7–82.4) | 1.25 (0.9–8.3) | 1.3 (1.2–1.7) | 4.28 | 0.34 |
FI = Fiducial Intervals; RR50 = Resistance ratio determined by LD50 of given population/LD50 of most susceptible population (*); RRa50 = Resistance ratio determined by LD50 of given population/LD50 of SzSusc; 95% CL = 95% Confidence limits; χ2 = Chi-square for lack-of-fit to the probit model, and P = Probability associated with the chi-square statistic. (—) Data not available as no dose-response curve could be computed for the selected population SzPyrSel.