A formulation was developed from the metabolite(s) of Pseudomonas aeruginosa (IL5) and tested against 3 rd instar larvae of the olive fruit fly Bactrocera oleae, the most serious pest on olive cultivations in the world. In this study, we have isolated 115 bacterial strains from various ecological niches from the soil, water, dead insects and infested olives and tested their ability to protect the olive fruits against this pest. The results show a high mortality at pH = 6 observed 72 h later. The LC50 dosage for larvae of this insect species was 24.0784 µl/ml. Our results conclude that this bacterial strain may be used as natural biocides.