Biocidal radiuses of cycloxaprid, imidacloprid and lambda-cyhalothrin droplets controlling against cotton aphid (Aphis gossypii) using an unmanned aerial vehicle.

Abstract

Unmanned aerial vehicles (UAVs) are a recently advanced aerial spraying technology. However, the median lethal number of droplets (LN50 ) and biocidal radiuses (r50 ) of insecticides droplets sprayed by UAVs are still unknown. Therefore, we evaluated the LN50 and r50 of cycloxaprid, imidacloprid and lambda-cyhalothrin droplets associated with adjuvant controlling against Aphis gossypii. A small UAV and Potter spray tower (PST) were used to generate different size of droplets (Dv0.5 = 185 ± 5 and 43 ± 2 μm). The mortality of A. gossypii showed a droplet density-dependent process. At the concentration of 5 g L-1 , the LN50 of lambda-cyhalothrin, imidacloprid and cycloxaprid droplets sprayed by the UAV were only 49.2, 34.6 and 19.7 droplets cm-2 , respectively, and the r50 were 0.57, 0.68 and 0.90 mm, respectively. The LN50 values were negatively correlated with insecticide concentrations, but the r50 values increased with the increasing concentrations. Although cycloxaprid is less toxic to A. gossypii than lambda-cyhalothrin, cycloxaprid had a larger r50 than lambda-cyhalothrin due to its translocation ability. Furthermore, cycloxaprid had a relatively larger r50 than imidacloprid because it is more toxic to A. gossypii. Moreover, adjuvant silwet DRS-60 can significantly increase the r50 of droplets. Our results revealed that the r50 of a droplet was higher than its droplet size at tested concentrations. Smaller droplets generated by the PST had relatively higher insecticidal potential. The median lethal dose (LD50 ) and translocation ability of insecticides and spray adjuvant contributed to their r50 . Therefore, ultra-low-volume spray with UAVs is feasible to control cotton aphids. © 2020 Society of Chemical Industry.