author(s)
Abhilisa Mudoi, Purnima Das and Lakshmi Kanta Hazarika

abstract
A laboratory experiment was conducted in the Physiology Laboratory, Department of Entomology, Assam Agricultural University Jorhat-13 during 2014-2016 to study the comparison of Beauveria bassiana (KR855715) strains viz., KR855715, IMI335352 and MTCC-6095 against instars and adults of Periplaneta americana (L.) (Blattodea: Blattidae). The biological parameters of B. bassiana showed that the native strain, KR855715 radially grew highest (40.15±0.91 mm) and showed highest spore germination (83.13±1.06%) and conidial density (12.02×10⁷ conidia/ml). All the strains were infectious to P. americana. However, instars were more susceptible than the adults. 100 percent mortality was recorded in case of 1^st and 2^nd instars (KR855715) and 40 (IMI335352) and 24 (MTCC-6095) per cent in 1^st instars. With respect to 2^nd instars, the mortality was found to be 36 (IMI335352) and 18 (MTCC-6095) per cent only. Similarly, mortality of 3^rd, 4^th, 5^th instars and adults varied between 16 (MTCC-6095) to 72 (KR855715), 20 (MTCC-6095) to 68 (KR855715), 16 (MTCC-6095) to 36 (KR855715) and 6 (MTCC-6095) to 26 (KR855715) per cent respectively at 9 days after treatment. The histopathological study revealed the presence of mycelial network of the fungus inside the insect body.