The LgPd NPs were synthesized biochemically, which are green NPs. The size of the NPs was around 20 nm, with an oval shape shown in the TEM of previously published data. These NPs were effectively trapped in mosquito larvae and caused the death of Aedes larvae due to ROS formation. Similarly, the NPs were treated with zebrafish embryos to check their toxicity level in higher animals, but it was observed that there was no near-death were recorded. The 10 µg/mL of LgPd NPs were enough to cause mortality in mosquito larvae, but a similar concentration in zebrafish embryos will not be lethal at all. The mechanism behind it was studied in these two species concerning the EPR effect and RES system and the generation of ROS supporting the proper development of higher animals and their effective body mechanism. This evaluation helps the biocompatible nature of prepared NPs and shows larvicidal activity against mosquito larvae. The current study explored the minor concentration, i.e. 10 µg/mL of LgPd NPs, successively killing the larvae, proving their larvicidal activity. ROS production deforms the larval structures; ROS formation was eliminated in zebrafish, and its effect was neutralized. This targeted therapy was helpful in theranostics purpose in living animals.