Two fatty acid synthase genes from the integument contribute to cuticular hydrocarbon biosynthesis and cuticle permeability inLocusta migratoria

Lipids of the insect cuticle have important roles in resistance against the arid environment and invasion of foreign substances. Fatty acid synthase (FAS) is an important enzyme of the insect lipid synthesis pathway. In the present study, we identified threeFASgenes from transcriptome data of the migratory locust,Locusta migratoria, based on bioinformatics analyses. Among them, twoFASgenes (LmFAS1andLmFAS3) are highly expressed in the integument of fifth instar nymphs. Suppression ofLmFAS1andLmFAS3by RNA interference caused lethality during ecdysis or shortly after moulting. The weight of the locusts and the content of lipid droplets were reduced compared with those of the control. The results of gas chromatography-mass spectrometry analysis showed that knockdown ofLmFAS3led to a decrease of both cuticular hydrocarbons and inner hydrocarbons (CHCs and IHCs) contents, especially the content of methyl branched hydrocarbons. By contrast, knockdown ofLmFAS1only resulted in a decrease in the IHC content, but not that of CHCs. By consequence, inLmFAS1-andLmFAS3-suppressed locusts, hydrocarbon deficiency reduced desiccation resistance and enhanced cuticle permeability and sensitivity to insecticides. These results indicate that LmFAS1 and LmFAS3 are essential for hydrocarbon production and cuticle permeability, which play influential roles in waterproofing the insect cuticle.