Abstract: 【Aim】 Brochosomes, covering on the body surface of the tea green leafhopper, Empoasca onukii, actively make their integument superhydrophobic. It is unclear whether the dynamic of insecticide droplets is influenced by brochosomes after droplets fall on insect body. This study aims to clarify the barrier effect of brochosomes on the resistance of E. onukii adults to the permeability of insecticide droplets. 【Methods】 Rhodamine B (RhB) was added into the test insecticides (bifenthrin and indoxacarb) as the indicator, and the dynamics of behaviors of E. onukii adults including rolling off, drying out, or swept away insecticide drops in 24 h after spraying of bifenthrin (1.25 and 0.05 mg/L) and indoxacarb (0.006 and 0.0009 mg/L) were observed and recorded by using photographic microscope. The relationship between the size of insecticide droplets and the deposition shapes after drying out on the leafhopper wings was analyzed. The contact angles between the insecticide droplet and the leafhopper forewing with brochosomes or brochosomes removed were measured. The brochosome densities on different hydrophobic wings were calculated. Both the insecticide droplets and granules of droplet deposition swept off from the leafhopper body were collected and observed under scanning electron microscope to verify the attachment of brochosomes. And the contact micromorphology of the dried solute of insecticide droplets with brochosomes on the leafhopper wings was observed. 【Results】 Spherical insecticide droplets could not autonomously roll off from the wings of E. onukii adults, and 72% of leafhoppers stood still until insecticide droplets on the wings dried out. Insecticide droplets were changed into granules or spots in irregular shape after evaporation, and the drying types of the droplets depended on the hydrophobicity of wing surface, but were unrelated to the droplet size. All the insecticide granules on the wings of E. onukii adults were swept away by grooming in 24 h after evaporation of droplets. On the hydrophobic leafhopper wings, the contact angle of droplet was 141.63±8.06°, and the drying droplets turned into granules, with the brochosome density of 6.1±1.2 particles/μm², while the drying droplets turned into spots on the wings with low hydrophobicity, and the brochosome density of 2.2±0.9 particles/μm². The SEM images showed that there were numerous brochosomes accumulated on the surface of insecticidal droplets and granules which were groomed away by E. onukii adults. Some brochosome agglomerates were found on insecticide spots and granules, and some were integrated with the dried solute residue. 【Conclusion】 The spherical shape of insecticide droplets on the wings of E. onukii adults are generated under the uniform distribution of superhydrophobic brochosomes. That insecticide droplets turn into granules after evaporation is related to the superoleophilicity and agglomeration of brochosomes. In addition, the detachment of brochosomes contributes to the removal of insecticide granules by grooming of E. onukii adults.

Key words:  Empoasca onukii, brochosome, superhydrophobicity, insecticide spray droplet; droplet evaporation, grooming