LmABCG-4C regulates cuticular barriers in both tarsi and body integument in locusts

Insects face their environment with their cuticle that protects them against desiccation and penetration of xenobiotics such as insecticides. Especially the tarsi contact the environment directly and are therefore the primary site of xenobiotic uptake. The major components of the outward and inward cuticle barrier are lipids including cuticular hydrocarbons (CHCs). Here, we studied the function of the putative lipid transporter ABCG-4C in barrier construction in the migratory locust, Locusta migratoria. It localizes to the cell membrane and cytoplasm of lipid-synthesizing oenocytes and epidermal cells. RNAi-mediated silencing of LmABCG-4C resulted in over 90% nymph mortality during molting, accompanied by increased desiccation susceptibility and enhanced xenobiotic penetration. Ultrastructural analysis revealed aberrantly thickened exocuticle and reduced lipid deposition in the envelope layer in dsLmABCG-4C-treated locusts, with concurrent declines in total cuticular lipid and CHC contents, confirming that LmABCG-4C is essential for maintaining cuticular lipid integrity and barrier function. LmABCG-4C expression was higher in tarsi than abdominal integument, indicating its key role in direct environmental contact sites. TEM results showed a loose and less organized tarsal cuticle compared with the compact and well-ordered abdominal cuticle. Deltamethrin bioassays further confirmed weaker barrier efficiency in tarsi. Our results demonstrate that LmABCG-4C is required for CHC transport and cuticular lipid barrier integrity in L. migratoria, and highlight structural and permeability differences between tarsal and abdominal cuticles. This work identifies LmABCG-4C as a promising target for RNAi-based pest management and provides novel insights into the functional differentiation of insect cuticular barriers across distinct body parts.