Studies on the Pathogenicity of Granulosis Virus of the Sugarcane Shoot Borer, Chilo infuscatellus Snellen

The granulosis virus of the sugarcane shoot borer. Chilo infuscatellus Snell., was found effective when applied as egg treatment. The mortality of larvae hatched from virus-coated eggs ranged from 26.34 to 81.17 percent at 10³ to 10⁹ OB (occlusion bodies)/ml respectively. The first and second instar larvae were found highly susceptible when fed with virus-contaminated food. The mortality varied from 69.05 to 94.67 per cent at 10³ to 10⁷ OB/ml. When microfed with the virus, third, fourth and fifth instar larvae were killed to an extent of 81.44, 64.15 and 54.62 per cent respectively, when the different doses were considered together. At the highhest dose tried (10⁷ OB/larvae), the virus caused 100.0, 81.90 and 72.01 percent mortality in third, fourth and fifth instar larvae respectively. The median lethal dose (LD₅₀) of the virus was 1061.2 and 8128.3 OB in third and fourth instar respectively. The LT₅₀ decreased with increase in age of the larvae or decrease in the dosage of the virus.