Abstract
Ultraviolet (UV) sunlight is considered to be the core factor reducing efficacy of bio-pesticides especially under the sunny-field conditions. The effectiveness and persistence of two bio-pesticides neem plant extract and spinosad were evaluated under the simulated and field conditions against the cotton army worm, Spodoptera littoralis (Boisd.) and the beet armyworm Spodoptera exigua (Hubner). Our findings indicate that persistence of both the bio-pesticides was significantly reduced at 21 day post-application when tested against first instar larvae of the S. exigua. However, the use of natural UV protectants henna and clove, screened in the present study had conserved the effectiveness of both bio-pesticides at 21-day post treatment against the neonate larvae of S. exigua. In contrast, when the bio-pesticides were applied against neonate larvae of S. littoralis, only spinosad formulated with green tea and clove was found effective at 1 day post-application with 86% and 55% mortality, respectively. When these pesticides were applied against second instar larvae, again spinosad blended with clove was showing mortality of about 50% at 3 days of application, whereas all other formulations caused very low mortality. Thus, the present data conclusively demonstrate that the bio-pesticides persistence could be enhanced by using extracts of henna and clove and that their application could be effective only to newly infested crops with neonate larvae.