Lipid utilization in adult Pieris brassicae with special reference to the rôle of linolenic acid

Fatty acids of adult Pieris brassicae and the incorporation of dietary linolenic acid-1-¹⁴C into adult (and egg) lipids were analysed 1 and 9 days after ecdysis. Females grown on a leaf diet retained palmitic, palmitoleic, and oleic acids but lost linoleic and linolenic acids during adult life, while males utilized their fatty acids more evenly. On an artificial diet both sexes retained palmitic acid but utilized palmitoleic and oleic acids. In both cases females laid eggs with a high palmitic and oleic acid content.Analysis of thorax flight muscles (artificial diet) revealed that 67·9% of the lipids in 1-day females and 83·6% in 9-day females was phospholipid (PL). During adult life linolenic acid increased in thorax neutral lipids (NL) from 14·6 to 20·0% in females and from 18·5 to 30·0% in males. Males incorporated more linolenic acid-1-¹⁴C especially in fat body and flight muscle PL than females. The majority of this was recovered from phosphatidyl cholines (PTC) in 1-day adults whereas in 9-day adults phosphatidyl ethanolamines (PTE) and another compound, most likely cardiolipin, contained more label (29·0% in PTC, 33·1% in PTE, 34·9% in cardiolipin, and 2·0% in sphingomyelin in the thorax of females). The females also incorporated the label into egg lipids (42·2% in PL, 57·8% in NL). There was recovered from PTC 54·5% of the label in egg PL.Most of the label in thorax NL was found to be in free fatty acids (FFA). The label disappeared from triglycerides during adult life and tended to accumulate in FFA (82·7% in 9-day females) while in diglycerides the label did not vary during adult life (17·2% in 9-day post-emergence females). PTC apparently is a fairly labile PL type which is utilized in muscle whereas PTE and cardiolipin may be more structural in function and accumulated more label from linolenic acid with increasing adult age. Linolenic acid, then, essentially is a structural fatty acid and its rôle appears to be mainly in the structures of flight muscle membranes and organelles.