Single dose screening assay of nine isolates of entomopathogenic fungi against rice gundhi bug, Leptocorisa acuta (Thunb)

Abstract

Single dose screening assay was conducted using nine isolates of entomopathogenic fungi to compare their bioefficacy in managing rice bug, L. acuta. The virulence of different isolates varies with different factors viz., host insect, environmental conditions etc. Hence, it is very important to identify the most potent pathogen in biological control using entomopathogenic fungi. The isolates used in experiment were Beauveria bassiana (Balsamo) Vuillemin (Bb 5 -NBAII isolate and Bb 21-KAU isolate), Metarhizium anisopliae (Metschnikoff) Sorokin (Ma 4- NBAII isolate) and the indigenous fungi viz., Aspergillus flavus Link. (Af-m1), B. bassiana (Bb-m2, Bbm3, Bb-m4 and Bb-m5) and M. anisopliae (Ma-m1). For effective comparison of the bioefficacy of different isolates, experiment using the same dose of all isolates is essential. The spore concentration used against third instar nymphs of L. acuta was 108 spores ml−1 and that evaluated against adults of L. acuta was 109 spores ml−1 based on the preliminary trials conducted. It is of common belief that local isolates show superior performance. But in our experiment, the local isolates (Bb-m2, Bb-m3, Bb-m4 Bb-m5 and Ma-m1) were not that virulent. B. bassiana (Bb-5) and M. anisopliae (Ma-4) showed superior performance in causing disease to both nymphs and adults of L. acuta compared to all other isolates.