Efficacy of local isolate of Nomuraea rileyi (Farlow) Sampson against Helicoverpa armigera (Hubner)

A laboratory experiment was conducted to determine the efficacy of local isolate of entomopathogenic fungi Nomuraea rileyi (Farlow) Sampson against Helicoverpa armigera Hubner. The present investigation was carried out at Mycological Research Section, Department of Plant Pathology, Assam Agricultural University, Jorhat, Assam, India during the period 2013-2014. Different spore concentrations were adjusted and comparison was made with Malathion 50EC @ 1.5ml/l. Observations on larval mortality of 4th instars H. armigera were recorded at an interval of 24hrs upto 10 days of post treatment. The results revealed that N. rileyi was highly virulent and infected the larvae in a dose dependent manner. At the highest concentration of 1 × 109 spores/ml, 17.40 % of the larvae were killed in 4 days and subsequently observed to be 85.92% at 10 days after treatment. At the next lower dose (1 × 108) total mortality was recorded to be 78.89%. The conidial concentration at 1 × 107, 1 × 106 and 1× 104 conidia per ml caused 71.85%, 68.15% and 39.25% mortality respectively, with a minimum mortality of 25.14% at 1 × 102 concentration. The LC50 value of N. rileyi tested on 4th instar larvae of  H. armigera was found to be 2 × 104 conidia/ml at 10 days. Thus, field studies on combine application of the N. rileyi along with the selective pesticides will be a useful strategy for integrated pest management of H. armigera.