Toxicity of PDKV Bt strains against okra shoot and fruit borer Earias vitella (Fab.)

The present investigation was carried out during the year 2023-2024 in the Department of Entomology, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola. The local Bt isolates viz., PDKV-SGd-1, PDKV-SY-4, PDKV-SA-6, PDKV-SAk-6, PDKV-I-3, PDKV-SGn-5, PDKV-SAk-9, PDKV SBn-2, PDKV-SA-18, PDKV-SGn-4 and PDKV-SA-20 along with Btk HD-1 as standard check were used. The endotoxins from these Bt strains were isolated following method of lactose co-precipitation method and used for conducting the toxicity bioassays against the 2nd instar larvae of Earias vitella. The lowest median lethal concentration (LC50) was recorded by PDKV-SGd-1, followed by PDKV-SY-4 followed by PDKV-SA-6 and these strains were found more effective than standard Btk HD-1. The rest of strains however found at par in toxicity to that of the standard Btk HD-1. The computation of relative toxicities indicated that Bt isolate SGd-1, SY-4 and SA-6 were 1.32, 1.28 and 1.25 fold more toxic than lowest toxic Bt isolate (i.e. SAk-6).