Influence of host egg age on parasitic potential of the entomophagous, Telenomus remus Nixon (Hymenoptera: Scelionidae) against the Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) and investigations on the developmental biology and ultrastructure of egg parasitoid immature stages

Abstract Background Biological control through augmentative release of egg parasitoids is a potential tool in integrated management of field crop pests. The egg parasitoid, Telenomus remus Nixon (1937) (Hymenoptera: Scelionidae), is found promising against the fall armyworm, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) in different parts of the world. However, fundamental information on the parasitic capabilities with reference to the host eggs of progressing ages is very limited. The investigations reported herein focused on the influence of host egg age on the parasitic potential, developmental biology and morphological features of the sexes of T. remus that could aid in decisions on their field release. The laboratory experiments were carried out with FAW egg masses of different ages (24, 48 and 72 h old). Host eggs glued to paper strips (3 × 5 cm) were offered to T. remus for parasitization at the parasitoid: host ratio 1:40 under standard laboratory conditions. Developmental biology of immature stages of T. remus and the adult sexual dimorphism were studied through stereomicroscopic and scanning electron microscopic examinations on 24 h old FAW egg masses parasitized by T. remus . Result Parasitic potential of T. remus on FAW eggs of different ages indicated the highest level of parasitization on 24 h old eggs with 98.2% parasitization, followed by 48 h old eggs and 72 h old eggs of the host were avoided by the parasitoid female and hence no parasitism occurred. The developmental duration of T. remus on 24 h old FAW eggs was recorded as 9.61 days and 48 h old eggs as 9.52 days, respectively. Microscopic examinations revealed the presence of six immature bio-stages viz., egg (1 day), two larval instars (each 1 day), pre-pupal (1 day), pupal (5 days) and adult stage with a total developmental duration of 9 days. T. remus adults can be differentiated by the morphology, type and number of antennal segments. The scape or the basal antennal segment was slender and longer in males, whereas shorter in females. T. remus female has a club typed antenna with 11 segments, while male has geniculate antenna with 12 segments. Conclusions The parasitoid exhibited selective preference for fresh stages of eggs than the matured ones indicating requirement of early field interventions coinciding with fresh brood emergence of FAW. Among the six stages of development, the pupal duration was found to be the longest in the study indicating that in augmentative biocontrol, host eggs with fully developed parasitoid stages, especially the pupal stage could be the appropriate one for field deployment.