Efficacy of some microbial insecticides on larval mortality of diamondback moth (Plutella xylostella L.)

Diamondback  moth (Plutella xylostella L.) is one of the major pests of all cruciferous crops and  it  can  survive  in  all  the  agro-climatic  zones  of  India.  The  marketable  crop  loss  caused  by Diamondback  moth  (DBM)  varies  from  52%  to  100%.  The  use  of  entomopathogenic  micro-organisms  proves  to  be  very  efficient  in  pest  management.  The  efficacy  of  three  commercial microbial insecticides viz., Bacillus thuringiensis  (Green Lipel),  Beauveria bassiana (Multiplex  Baba) and Metarhizium  anisopliae  (Green  Pacer)  at  different  doses  was  tested  on  the  basis  of  percent  larval mortality  when  3  day  old  larvae  of  DBM  were  exposed  to  the  formulations.  All  the  microbial formulations were effective in suppressing larval growth and development as compared to untreated control.  Larval  death  could  be  markedly  observed  after  72  hours  of  treatment.  Treatment  with Beauveria bassiana @ 4g/l gave the highest larval mortality of 27.50% after 72 hours of treatment. At 
96 hours after treatment, percent larval mortality caused by B. bassiana @ 5g/l recorded maximum mortality of 55.00% which was observed to increase from 25.00% at 72 hours after exposure. After 120 hours of treatment, mortality of larvae exposed to the microbial insecticides was observed to be highest with larval mortality ranging from 25.00% to 62.50% for all the microbial formulations. Of which, the highest percent mortality of larvae was observed with treatment B. bassiana @ 5g/l that gave 62.50% mortality. Lower mortality could be recorded with lower doses of microbial insecticides as compared to the mortality due to higher doses. B. thuringiensis proved to be least effective among the tested microbial formulations