Анотация: Parasitoid behavior was monitored to investigate the ability of Euplectrus plathypenae (Howard) (Hymenoptera: Eulophidae) to distinguish between healthy and infected with nucleopolyhedroviruses Spodoptera exigua (Hubner) and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) larvae. Third and fourth instars (L3 and L4) of both Noctuidae species were used in the present study. When E. plathypenae females were given choice between healthy and virus-infected S. exigua and S. frigiperda hosts, the adult females exhibited marked preference (P < 0. 05) for the healthy hosts of the both instars of the two species. The ovipositional discrimination study also showed that the correlation between the percent parasitism of healthy and virus-infected L3 larvae was significantly higher than the correlation between parasitized healthy and virus-infected L4 S. frugiperda larvae. In S. exigua larvae the oposite correlation between the two instars has been observed.. - The results proved that E. plathypenae females and the multiple-enveloped nucleopo-lyhedroviruses of S. exigua (SeMNPV-SP2) and S. frugiperda (SfMNPV) did not significantly compete for the same type of host larvae and are, generally, compatible. Since the healthy and virus-infected larvae were different in a number of ways, several factors may have contributed to the behavioral discrimination evidenced