Two different Rhabditida species (Nematoda: Rhabditidae) Parasitorhabditis platidontus n. sp. and Cruznema campestris n. sp. are described and illustrated from the larvae of Cyclocephala signaticollis (Coleoptera: Scarabaeidae) from Buenos Aires province, Argentina. Parasitorhabditis platidontus n. sp. is characterized by having 4 odontoplates in the stoma and the vulva is at 80% of the length of the body. Cruznema campestris n. sp. can be distinguished by the presence of 4 odontoplates and the arrangement of the male genital papillae, 9 pairs, of which 4 are preanal and 5 postanal.