1. Introduction
Aquatic moths of Lepidoptera, Crambidae, and Acentropinae inhabit moist environments. For example, the larvae of genus Eoophyla all live in streams, and their wing surfaces are highly hydrophobic after a long period of evolution. Currently, there are only some sporadic reports on the classification and agricultural control of aquatic moths, and reports on hydrophobic properties and their surface scales are very limited.
2. Methods
We used a contact angle measuring instrument and SEM to study the hydrophobicity and microstructure of three aquatic moths Eoophyla ochripicta, E. menglensis, and E. melanops (Crambidae, Acentropinae) and a non-aquatic moth Conogethes punctiferalis (Crambidae, Pyraustinae).
3. Results
Our research results show that the wing surfaces of all three aquatic Eoophyla moths have strong hydrophobicity, and the contact angle of the minimum water drop volume was 15 µL (ranging from 139.3° to 143.0°), but the contact angle of the non-aquatic moth was only 133.9°. The microstructures of the wing surfaces of the three aquatic Eoophyla moths are similar: the surface of the scales consists of sub-micron longitudinal ridges and laterally connected ribs, and the spacing between the longitudinal ribs is 0.8~1.69 µm, exhibiting a grid shape. Conversely, the laterally connected ribs of C. punctiferalis are incomplete.
4. Conclusions
Due to the presence of the wing surface microstructure of aquatic moths, and because the scale of the structure is much smaller than the diameter of the droplet, this leads to the formation of air pockets under the droplets, which are unable to fully fill the grooves of the surface. Thus, the wing surface exhibits stronger hydrophobicity. However, the microstructure of C. punctiferalis can make water droplets have more contact with the wing surface, so the hydrophobicity is less favorable than that of aquatic Eoophyla moths. Researching the relationship between the hydrophobic properties of the wing surface and its structure can provide an experimental and theoretical basis for the preparation of hydrophobic biomimetic materials.
Author Contributions
Conceptualization, M.S. and F.C.; methodology, M.S.; validation, M.S., A.L. and T.M.; investigation, T.M.; resources, F.C.; writing—original draft preparation, T.M.; writing—review and editing, M.S. and A.L. All authors have read and agreed to the published version of the manuscript.
Funding
This work was supported by the National Natural Science Foundation of China (grant nos. 31772513 to M.S. and 32070470 to A.L.).
Institutional Review Board Statement
Ethical review and approval were waived for this study due to where no specific permits were required for the described studies.
Informed Consent Statement
Not applicable.
Data Availability Statement
Data available on request from the authors.
Conflicts of Interest
The authors declare no conflict of interest.
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