Efficacy of selected adjuvants for protecting Spodoptera litura nucleopolyhedrovirus from sunlight inactivation

Efficacy of selected adjuvants for protecting Spodoptera litura nucleopolyhedrovirus (SpltNPV) from sunlight inactivation was tested in direct sunlight exposure bioassays and in the field on virus-treated Brassica chinensis var parachinensis plants. All adjuvants, except palm oil, gave significant protection to the virus after 16 h of sunlight exposure, as shown by the larval mortalities. Cumulative mortalities after 14 days show that the virus + Tinopal treatment and the virus not to sunlight treatment attained 100% mortality, while the virus in riboflavin treatment and the crude brown sugar treatment caused mortality of less than 30%. However, the LT50 value of virus + Tinopal was 1.2 times lower than the unexposed virus. All virus-treated plants in the field trials had higher yields and lower damage indices than the control plants. Unlike the results from direct sunlight exposure bioassays, adjuvants, including virus + Tinopal LPW, did not significantly enhance efficacy of the virus against early instars of S. litura in the field. The unformulated virus was as effective as virus + Tinopal LPW and Nurelle-D in protecting the plants from infestation. Thus, in a well-planned pest management program, SpltNPV, without any adjuvant, can be used effectively for controlling S. litura on B. chinensis var parachinensis.