Bioactivity of different formulations of Bacillus thuringiensis (Berliner) and

their combinations with endosulfan against pod borer Helicoverpa armigera

(Hubner)

RUCHIRA TIWARI and V.K. SEHGAL

Department of Entomology,

College of Agriculture,

G. B. Pant University of Agriculture and Technology,

Pantnagar-263145 (U. S. Nagar, Uttarakhand)

ABSTRACT

Bioassay studies carried out in the laboratory to determine the effect of sublethal doses of  four commercial formulations of Bacillus thuringiensis (Berliner) (Bt) i.e., Bt var kurstaki viz Dipel 8L (Bt1 ), Dipel 2x (Bt3), Bioasp, Biolep, and two different Bt strains, Bt  var aizawai (Centari) (Bt₂ ), and Bt var thuringiensis (Biotox) alone and in combination with endosulfan for their bioactivity against 0-24 hr old neonate larvae and 7 days old larvae of H .armigera. Growth and development of neonate larvae was drastically suppressed in all Bt treatments alone and in combination with endosulfan as 100 per cent mortality was observed after 1 to 3 days of feeding on treated diets. Similarly, higher doses of  Bt and half dose of Bt + half dose of endosulfan were found highly effective against 7 days old larvae with 10.7 per cent pupation but all the pupae were deformed and did not produce  any adult moth. Relative toxicity of all Bt treatments using artificial diet technique of bioassay showed that Bt var. kurstaki (Bt₁ ) was the most effective with the lowest value of LD₅₀ (0.0013) followed by Bioasp, Biolep, Biotox and Bt₂  with LD₅₀ values of 0.0015 and 0.0015, 0.0018, 0.0028, respectively, for 7 days old larvae for the feeding period of 72 hours. Bt₁  was found 27.7 times more toxic than endosulfan and the order of relative toxicity was found to be Bt₁> Bioasp> Biolep> Biotox> Bt2 to H. armigera larvae. All the concentrations of Bt have adverse effect on growth and development of the test insect. Increased larval mortality, larval period, growth inhibition, decreased pupation, darkening of larval skin and failure in adult emergence were recorded with the increased dose of Bt under laboratory conditions.