Polyunsaturated fatty acids of mosquitos reared with single dietary polyunsaturates

Abstract

Stock adults of Culex pipiens and tarsalis reared in crude media had a third of their phospholipid fatty acids as polyunsaturates, mainly 18C but including prominent proportions of arachidonic (20:4 n6) and eicosapentaenoic (20:5 n3) acids. Adults reared with synthetic media devoid of polyunsaturated fatty acids and therefore unable to fly at emergence contained no more than trace amounts of any polyunsaturate. With synthetic media containing single polyunsaturates the following findings emerged. Of four polyunsaturates known to be highly effective essential fatty acids individually 20:4 n6 or 20:5 n3 appeared unchanged in tissue phospholipids in proportions reflecting dietary concentrations; dietary 22:4 n6 or 22:6 n3 (docosahexaenoic acid) appeared also as 20:4 n6 or 20:5 n3, respectively, retroconverted from the administered dietary fatty acids, which were detected only in traces. Two moderately effective dietary fatty acids, 18:3 n6 (γ-linolenic) and 20:3 n6 (homo-γ-linolenic), which support weak flight at emergence, appeared in tissue phospholipids respectively as 18:3 n6 only, or as similar proportions of 18:3 n6 and 20:3 n6, this latter indicating shortening to the 18C analogue as well as accumulation of the dietary 20C acid. Six other polyunsaturates [18:2 n6 (linoleic), 18:3 n3 (linolenic) and their 20C and 22C analogues], all considered slightly effective as essential fatty acids although unable to support proper flight, appeared in tissue phospholipid in dose-related proportions as the 18C basal n6 or n3 family analogues, with only traces of the higher analogues when these were the dietary fatty acids provided, indicating sequential chain shortening within each series, n6 or n3, no interconversion of n6 and n3 members (also shown by all other data), and efficient accumulation of the resultant 18C polyunsaturates. These findings show no capability for de novo synthesis of polyunsaturated fatty acids, afford an insight into the metabolic interrelations of diet-derived polyunsaturates and indicate a primary importance for endogenous arachidonic and eicosapentaenoic acids in mosquito essential fatty acid physiology.