Nucleopolyhedrovirus is an effective biocontrol agent but for its biggest disadvantage of short persistence under sunlight conditions. In this study, 10 plant extracts were evaluated as ultraviolet (UV) protectants to improve the persistence of Spodoptera littoralis multiple-embedded nucleopolyhedrovirus (SpliMNPV) against cotton leafworm (Spodoptera littoralis Boisduval). In the primary lab screening test, 5 out of 10 additives (cloves, henna, green tea, pomegranate, and grape extracts) presented a high rate of virus protection with original activity remaining (OAR) percentage of 100%, 97%, 91%, 90.6%, and 77%, respectively, when used at a concentration of 1% and exposed to UVB for a period of 1 h. A secondary screening was then performed with these best five extracts at a concentration of 0.5% and for an exposure timing of 5 h to UVB. Among these, clove and henna that showed highest protection with OAR values of 96.6% and 76.5%, respectively, were selected for the field trials. When applied on cabbage in the field during sunny summer conditions, clove and henna extracts enhanced the persistence of SpliMNPV by twofold. These findings are encouraging to be applied in the field studies.
Keywords: Noctuidae; SpliMNPV; Spodoptera littoralis; biological control; plant extract.
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