Effect of organic amendments on infectivity of entomopathogenic nematodes against Brahminacoriacea (hope)

Background: Motility and persistence of entomopathogenic nematodes areinfluenced by numerous interacting factors such as temperature, soil moisture, soil texture, relative humidity and UV radiations. The most important factor is soil texture, because soil particle size, composition and organic matter content in soil strongly influence the nematode motility, infectivity, development, reproduction and survival of entomopathogenic nematodes. Results: The bioassay studies were done to study the effect of organic amendments on the infectivity of Heterorhabditis indica (Poinar) against I-III instar grubs of Brahminacoriacea (Hope) under laboratory conditions. The virulence of H. indica was tested in soil amended with different organic substrates,i.e. cocopeat, vermicompost, vermiculite and FYM, used in different combination ratios of 9:1, 8:2 and 7:3 of soil and substrates.In sand, the LC50 values of grubs (I-III instar) were computed to be 233.33-307.67 IJs/ml. H. indica displayed more or less the same virulence, irrespective of thesoil and sand media used for rearing of grubs. In soil:FYM ratios of 9:1, 8:2 and 7:3, the LC50 values of the respective instars ranged from 277.83-339.14, 243.54-290.26 and 216.08-250.36 IJs/ml, respectively. In soil:vermicompost ratio of 9:1, 8:2 and 7:3, the LC50 values of H. indica against I-III instar grubs of B. coriacea were calculated in the range of 256.37-345.98, 214.19-282.33 and 168.75-240.53 IJs/ml, respectively. It has been observed that the addition of vermicompost produced more or less similar effects as noticed with FYM. The LC50 values of H. indica against I-III instar grubs ranged from 337.54-545.77, 293.07-455.60 and 247.72-404.65 IJs/ml in cocopeat and soil ratios of 9:1, 8:2 and 7:3, respectively. The virulence of H. indica to I-III instar grubs decreased with the addition of cocopeat in soil. In different soil:vermiculite combinations, the LC50 values of H. indica against I-III instar grubs were calculated to be 530.83-905.79, 456.93-771.52 and 396.71-668.03 IJs/ml, respectively. Maximum virulence of H. indica was observed in vermicompost, followed by FYM and cocopeat.