The aim of this study was to investigate insect derived bacteria for the ability to dissolve insoluble soil phosphate to release soluble phosphorus compounds, available to plants. Bacterial isolates were obtained from Diabrotica virgifera, Hermetia illucens, Oulema melanopus, and Ostrinia nubilalis. An in vitro evaluation of phosphate solubilization ability on Pikovskaya’s medium was done and the Phosphate Solubilizing Index (PSI) was calculated for each isolate. Bacteria were tested in a greenhouse experiment on seeds of oats, wheat, triticale, barley and soybeans. After incubation, the weight and length of their aerial plant parts were measured. The highest increase in the weight of aerial parts was recorded for oats after using strain Om046 for inoculation (88.98%), then, wheat (Dv097, 31.43%), soybean (strain 96, 53.79%), and triticale (bacterial consortium, 36.9%). Bacteria used were identified as Lactococcus lactis (strains Om030 and Om046), Acinetobacter sp. (Dv123), Lactococcus garvieae (Dv097) and Rothia kristinae (strains 90 and 96). We showed that a successful application of insect derived bacteria for phosphate solubilization in soil, to promote plant growth, is possible. Innovative agriculture requires constant improvements in increasing crop growth. Thus, new sources of bacterial strains effectively promoting plant growth, are needed. We described a new source of plant growth-promoting bacteria that can be used in agriculture.