Background Baculoviruses are significant biocontrol agents of pests in agriculture; however, ultraviolet light B (UV-B) and high temperature inactivate them in the environment within a short time. Results In this study, formulations of Helicoverpa armigera nucleopolyhedrovirus Turkey isolate (HearNPV-TR) were prepared. Crude virus, the oil-based formulations of the virus, and a commercial H. armigera NPV product were exposed to UV-B light and various temperatures (28, 35, and 42 degrees C) at different periods (0, 1, 3, 5 h.). While the UV-B application decreased the virulence of crude virus up to 32% after 5 h. exposure, it decreased the virulence of oil-based formulation by (15%). Similarly, the virulence of the crude virus by 70% at 42 degrees C, while was reduced by 10% in the formulations at the same temperature. Therefore, 5% oil formulation was enough to keep the virulence of the virus underexposed to UV-B and high temperatures. LC95 values were calculated as 1 x 10(8) OBs/ml(-1) in concentration-response tests, and mortality rates were 90 and 92% in pot assays for commercial product and 5% oil formulation, respectively. Conclusions The results showed that 5% oil formulation of HearNPV-TR was an important biocontrol preparation to protect virus virulence under suppressive environmental conditions.