The effect of temperature, ultraviolet (UV) radiation and sunlight on the pathogenicity, yield and DNA genome pattern of the entomopathogenic virus SpliMNPV to the Egyptian cotton leafworm Spodoptera littoralis (Boisduval) was studied. The viral pathogenicity in terms of larval mortality, and yield in terms of polyhedral inclusion bodies/g larval body weight, significantly increased with the increase of temperature; with optimal temperature of 30 °C for viral yield. However, the pathogenicity significantly decreased with the increase of the exposure period, under the stress of both UV radiation and sunlight, in case of non-shielded exposed viral samples. In contrast, sunlight and UV had no significant effect on the viral pathogenicity in shielded exposed samples. The viral yield significantly decreased with the increase of the exposure period to UV radiation. The same pattern also held true for the exposure to sunlight in case of non-shielded exposed samples without using a UV filter. The viral DNA genome pattern was not affected under the stress of temperature, UV-radiation (shielded samples), sunlight using a UV filter (shielded or non-shielded samples), and sunlight without using a UV filter (shielded samples). Whereas, the intensity of the viral DNA, in non-shielded samples, decreased gradually with the increase of the exposure period to UV radiation and sunlight without using a UV filter.