Concentration of sodium dodecyl sulfate used in occlusion body extraction affects Spodoptera littoralis nucleopolyhedrovirus biological activity

Efficacy of a baculovirus as a biological control agent is evaluated according to biological parameters, median lethal dose (LD50) of the virus, and median lethal time (LT50) of infected larvae. Sodium dodecyl sulfate (SDS) is commonly used in concentrations of 0.1%–1% to extract infective units of the baculoviruses, occlusion bodies (OBs), from infected cadavers. Although several studies have shown disruption of OB structure by SDS, the effects of SDS concentrations on baculovirus biological parameters are not well known. Indeed, it is essential to detect the optimum SDS concentration for OB extraction to compare the activity of baculoviruses accurately. In our study, the effects of SDS (0.1%–2%) on baculoviral biological activity were examined using Spodoptera littoralis nucleopolyhedrovirus in third instar Spodoptera littoralis (Lepidoptera: Noctuidae) larvae. Use of 1% SDS in OB extraction caused the lowest LD50, while higher concentrations than 1% significantly increased the LD50. The differences between LT50 values at 0.1%–1% SDS were found to be insignificant; however, higher concentrations ( 1.0%) caused significant loss of biological activity. Therefore, 0.1%–1.0% SDS could be used for OB extraction; however, evaluation of LD50 and LT50 values together suggests that 1% SDS provides the best biological activity. The mode of action of SDS on baculovirus biological activity is discussed further.