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Virulence of Metarhizium anisopliae (Metschnikoff) Sorokin strain ESC-1 against the German cockroach, Blattella germanica (L.), was determined using 5 concentrations ranging from 83107 to 23109 spores per milliliter. The calculated LD50 value was 4.18 by 108 spores per milliliter (4.18 3 105 spores per cockroach). In vitro study was conducted to determine the compatibility of M. anisopliae strain ESC-1 with chlorpyrifos, propetamphos, and cyfluthrin. Insecticides did not affect conidial germination but did adversely affect the growth and sporulation of M. anisopliae strain ESC-1. The growth of M. anisopliae colonies on media amended only with 50 and 500 ppm of chlorpyrifos and 500 ppm of propetamphos treatments at 3, 6, and 9 d was significantly inhibited compared with the control. Similarly, sporulation was significantly reduced in treated colonies exhibiting partial colony growth. The colonies cultured on SDAY media amended with 50 ppm of chlorpyrifos had significantly reduced sporulation compared with the control and no sporulation was observed in colonies cultured on media amended with 500 ppm of chlorpyrifos and propetamphos.