The effect of zinc oxide nanoparticles, kaolin powder and Beauveria bassiana (Balsamo) Vuillemin in combination with Neemarin® against Bemisia tabaci and pupae of Eretmocerus mundus under field conditions

 Bemisia tabaci (Genn.)(Hem: Aleyrodidae)is considered as one significant pest in the agricultural products in Iran. In this research, the effects of ZnO NPs, kaolin, B. bassiana (EUTP105 Isolate) were assessed alone or in combination to Neemarin® compared to thiacloprid insecticide under field conditions on eggs and nymphs of B. tabaci and pupae of its parasitoid Eretmocerus mundus.

This research was handled in the research field of the scientific staff of the Cotton Research Center of East Iran, Kashmar, in a randomized complete block design with three replications in August 2019. The experimental plots were separately 6 m2 and 1.5 m. The recommended concentration of Neemarin® (15 mg L-1 AZA), thiacloprid (0.3 mL L-1), Kaolin (30 g L-1), a concentration of 20 mg L-1 of ZnO NPs, a concentration of 1×1010 conidia mL-1 of B. bassiana, half- concentration of Neemarin® (7.5 mg L-1 AZA) + 10 mg L-1 of ZnO NPs, half- concentration of Neemarin® (7.5 mg L-1 AZA) + 15 g L-1 of Kaolin and half- concentration of Neemarin® (7.5 mg L-1 AZA) + a concentration of 1×105 conidia mL-1 of B. bassiana were prepared which sprayed on upper and lower surfaces of cotton plants using a knapsack sprayer, equivalent to an application volume of 500 l ha-1. The control treatment was sprayed by water. The mortality of B. tabaci eggs and nymphs and pupal stage of E. mundus were calculated using Henderson and Tilton equation . To this purpose, five plants were randomly selected in each plot and three leaves from each one (top, middle, and bottom section of plant canopy) were excised and transferred to a laboratory. Two pieces of 1 cm2 from each leaf were chosen so that the units included into main vein. Total live eggs and nymphs of pest as well pupae of parasitoid in each sample unit were counted using a binocular. Samplings were handled one day before and 3, 7 and 14 days after spraying.

In 3 DAT (days after treatment), the most effective treatments on eggs and nymphs of pest were Kaolin + Neemarin® and thiacloprid, respectively. While, the least effective treatments were B. bassiana. In 7 DAT, Kaolin + Neemarin® and ZnO NPs exerted the highest and lowest mortality, respectively, on the eggs of pest, Neemarin® and B. bassiana exerted the highest and lowest mortality, respectively to the nymph. In 14 DAT, the highest efficacy on eggs and nymphs was observed in Kaolin + Neemarin® and Neemarin®, respectively, while the lowest efficacy both on eggs and nymphs belonged to B. bassiana. The highest and lowest mortality of the pupae of parasitoid in 3 DAT belonged to thiacloprid and B. bassiana, respectively. In 7 DAT, Neemarin® and ZnO exerted the highest and lowest mortality on the parasitoid pupae, respectively.  In 14 DAT, Kaolin exerted the highest mortality on the pupae of parasitoid that was followed by Kaolin + Neemarin®, Neemarin®, and thiacloprid. The maximum yield and benefit/cost ratio were observed in Kaolin + Neemarin®, followed by Kaolin treatments. 

Considering the results, ZnO NPs and Kaolin alone, or in combination to Neemarin® can be the suitable candidates as an alternative in the IPM programs of B. tabaci on the cotton field.