Efficacy of botanical extracts and entomopathogens on control of Helicoverpa armigera and Spodoptera litura
Interest in biological control of insect-pests of economically important plants has been stimulated in recent years by trends in agriculture towards greater sustainability and public concern about the use of hazardous pesticides. Botanicals and microorganisms have the capability to synthesize biologically active secondary metabolites such as antibiotics, herbicides and pesticides. In this investigation, washings of herbal vermicompost (called biowash; viz. Annona, Chrysanthemum, Datura, Jatropha, Neem, Parthenium, Pongamia, Tridax and Vitax) and plant growth promoting (PGP) bacteria [viz. Bacillus subtilis (BCB-19), Bacillus megaterium (SB-9), Serratia mercescens (HIB-28) and Pseudomonas spp. (SB-21)] and fungus (Metarhizium anisopliae) were evaluated for their efficacy against Helicoverpa armigera and Spodoptera litura. When the feed was treated with crude biowash for healthy larvae (4-day old), 42 and 86% mortality and 32 and 71% weight reduction over control was reported for H. armigera, while in the case of S. litura, it was between 46 and 74% larval mortality and 47 and 77% weight reduction over control. When healthy larvae were treated with PGP bacteria and fungus, the mortality rate varied between 59 and 73%, with 55 and 92% weight reduction over control on H. armigera, while for S. litura, 54 and 72% larval mortality and 44 and 79% weight reduction over control was reported. The results of the compatibility studies (entomopathogenic potential biowash of the botanicals with PGP bacteria and fungus) indicate that there was no definite sign of suppression of any of the botanicals on the PGP bacteria and fungus, except Datura with B. subtilis BCB-19, whereas, there was definite sign of enhanced growth of B. megaterium SB-9 with all the botanicals. Compatibility studies between PGP bacteria and fungus showed that all bacteria are compatible with each other except M. anisopliae. Crude biowash of the promising botanicals (Annona, Datura, Jatropha, Neem, Parthenium and Pongamia) were further fractionated on C18 solid phase extraction cartridge (SPE) and the resultant adsorbed and non-adsorbed fractions were tested against H. armigera. Results indicate that both adsorbed as well as non-adsorbed fractions showed significant mortality on H. armigera. Adsorbed fractions of all the six biowash showed mortality between 81 and 93% (64 and 73% for nonadsorbed fraction) over control and the weight reduction of the larvae was found between 73 and 91% (80 and 97% for non-adsorbed fraction) over control. It was therefore concluded that the aforementioned six botanicals and five entomopathogens has great potential in the management of H. armigera and S. litura.
Key words: Botanicals, entomopathogens, biowash, secondary metabolites, Helicoverpa armigera, Spodoptera litura.