Mortality Response of Helicoverpa armigera (Hübner) Larvae Fed on Tomato leaves Treated with HaNPV

Bioactivity of baculoviruses, being an important prerequisite for the intended use of such microbial biopesticides in IPM, was carried out by inoculating Helicoverpa armigera different age-group larvae (younger- 5-day old; 1.3 ± 0.1 cm and 34.8 ± 3.7 mg; medium-sized- 7-day old; 1.8 ± 0.1 cm and 57.8 ± 3.4 mg; and relatively older 9-day old; 2.5 ± 0.1 cm and 93.2 ± 3.1 mg) with the six serial graded concentrations of 1.23 x 10⁴ to 1.23 x 10⁹ occlusion bodies (OBs) of indigenous HaNPV (PAU 1-strain) through leaf-dip inoculum administration, using the tomato (cv. Punjab Chhuhara) leaves in the laboratory. An inverse relationship between the fed-virus concentration and the time taken to cause a particular level of larval mortality was conspicuously observed. The calculated lethal time (LT) values for younger larvae varied from 80.4 to 113.0 hrs (LT₂₅); 98.6 to 150.0 hrs (LT₅₀); 118.0 to 173.5 hrs (LT₇₅); and 135.0 to 184.6 hrs (LT₉₀) for the six virus concentrations tested. For medium-sized larvae, these LTs ranged between 93.3 and 162.5 hrs (LT₂₅); 132.0 and 213.6 hrs (LT₅₀); 162.3 and 241.0 hrs (LT₇₅) and 179.0 and 249.0 hrs (LT₉₀). For older larvae, LT₂₅ ranged between 133.6 and 184.0 hrs for the various virus concentrations in contrast to LT₅₀ of 168.0 to 192.0 hrs, which could be calculated only for three relatively higher virus concentrations of 1.23 x 10⁷ to 1.23 x 10⁹ OBs/ml. The calculated LC₅₀ values for younger, medium-sized and older larvae at 5, 7 and 8 post- treatment days were 2.96×10⁶, 9.0×10⁵ and 2.91×10⁶ OBs/ml, respectively. The bioactivity determination of HaNPV against H. armigera larvae thus, offered unique potential of this indigenous virus in ecosafe management on the tomato crop.