Determination of LD 50 and LT 50 of entomopathogenic nematodes against shoot borer (Conogethes punctiferalis Guen.) infesting ginger (Zingiber officinale Rose.)

Abstract

Study on the pathogenecity of four native entomopathogenic nematodes, Heterorhabditis sp. (IISR-EPN 01), Steinernema sp. (IISR-EPN 02), Oscheius sp. (IISR-EPN 08) and O.gingeri against shoot borer larva(SBL), by dose response and time exposure assay and determination of lethal dosages (LD50 ) and lethal time (LT50) by regression analysis. LD50 were calculated using four densities of test EPNs viz., 25, 50, 75 and 100 IJs/SBL and LT50 was calculated using one nematode density 100 IJs to mortality of SBL at 24, 48 and 72 hrs. Although the SBL was susceptible to test EPNs, there were differences among these EPNs in their ability to kill the insect. Among test EPNs,Steinernema sp. (IISR-EPN 02) and O.gingeri appears to be the most promising. The per cent mortality of SBL increased with the increase the dosage as well as exposure time. A positive correlation was found between dosages as well as exposure time and mortalirty. Probit analysis indicated that Oscheius sp. (IISR-EPN 08) required less number (48 IJs/larva), whereas Steinernema sp. (IISR-EPN 02) took less time (29 hrs) for desired mortality of SBL. This study will be helpful in the shoot borer management under field conditions.