Effects of ZnO nanoparticles and Kaolin in combination with NeemAzal-T/S against Bemisia tabaci and its parasitoid Eretmocerus mundus on cotton

Abstract

The cotton whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is an important pest of cotton which by transmitting plant pathogenic viruses cause damage and reduce lint quality. To reduce the use of chemical insecticides, effects of ZnO nanoparticles, Kaolin alone or in pairwise combination with NeemAzal-T/S against egg and second instar nymph of B. tabaci and pupae of its parasitoid Eretmocerus mundus Mercet were evaluated. The LC50 values of ZnO NPs, Kaolin and NeemAzal-T/S against eggs and nymphs of B. tabaci were 7.49 mg L-1, 24.89 g L-1, 6.83 mg L-1 AZA and 6.93 mg L-1, 18.36 g L-1 and 6.00 mg L-1 AZA 3 days after treatment, respectively. The LC50 values of ZnO NPs, Kaolin and NeemAzal-T/S against E. mundus were 11.30 mg L-1, 41.59 g L-1, 36.90 mg L-1 AZA, respectively 3 days after treatment. In the laboratory conditions, ZnO + NeemAzal and Kaolin + NeemAzal exerted a higher level of control on eggs and nymphs of the pest than either alone, while they had a lower level of negative effects on the parasitoid pupae, too. In the field conditions and at 7 DAT, Kaolin + NeemAzal was the most effective treatment on eggs of the pest, causing a 67.43% reduction, while NeemAzal-T/S was the most effective treatment on nymph (86.52% reduction), which was not different with ZnO + NeemAzal and Kaolin + NeemAzal. NeemAzal and ZnO exerted the highest and lowest mortality on pupae of the parasitoid, respectively. Based on the field studies, ZnO NPs at 20 mg L-1, Kaolin at 30 g L-1, NeemAzal-T/S at 15 mg L-1 AZA and mixing equal volumes of NeemAzal-T/S (7.5 mg L-1 AZA)+ZnO NPs (10 mg L-1) and NeemAzal-T/S (7.5 mg L-1 AZA)+ Kaolin (15 g L-1) can be suitable candidates in IPM programs of B. tabaci field condition.