Thanks for your help. I tried with gene.idtype = "KEGG". But it not mapping the genes and throws warnings like,
Warning: None of the genes or compounds mapped to the pathway!
Argument gene.idtype or cpd.idtype may be wrong.
Warning: No annotation package for the species osa, gene symbols not mapped!
Info: Working in directory /home/genome/KEGG
Info: Writing image file osa00195.pathview.png