# Ultrastructural Changes in Final Instar Larvae of Papilio polytes (Lepidoptera: Papilionidae) Lead to Differences in Epidermal Spreading of Water and Adjuvants

## TL;DR

This study examines how the epidermal structure of Papilio polytes larvae changes during development and how these changes affect their wetting properties with water and adjuvants.

## Contribution

The study reveals how epidermal ultrastructural changes correlate with wetting properties and adjuvant infiltration in P. polytes larvae.

## Key findings

- Complex epidermal structures increase hydrophobicity during larval development.
- Cationic adjuvants infiltrate complex structures best, while organosilicon adjuvants work best on simple structures.
- The findings support biomimetic design and adjuvant selection based on developmental epidermal changes.

## Abstract

Papilio polytes is a cosmopolitan Lepidoptera species of controversial use and management. It remained unclear how its epidermal ultrastructure changes during development and how this affects its wetting properties in relation to water and pesticide adjuvants. In this study, the epidermis of P. polytes was systematically examined at the important feeding stage (from 3rd to 5th instar). Its ultrastructure was quantitatively observed by scanning electron microscopy. Its wetting properties towards the three main types of adjuvants and water were evaluated by contact angle. The chemical functional group differences between different instars and different adjuvant treatments were analyzed by mid-infrared spectroscopy. The correlation between the ultrastructural deformation and variations in wetting properties was verified by simulation tests. It was found that the complication of the epidermal structure was the leading factor for the significant increase in hydrophobicity during development. Cationic adjuvants had the best infiltrating effect on complex epidermal structures and organosilicon adjuvants had the best infiltrating effect on simple epidermal structures. The results provide data for biomimetic design for different wetting properties and suggest the feasibility and advantages of selecting pesticide adjuvants based on developmental changes in the structural characteristics of the insect epidermis.