FATTY-ACID CONTENT AND ENZYMES OF FATTY-ACID METABOLISM IN OVERWINTERING COLD-HARDY GALL INSECTS

Fatty acid content and enzymes of fatty, acid metabolism were studied in overwintering larvae of two cold-hardy gall insects, the freeze-tol erant fly, Eurosta solidaginis and the freeze-avoiding moth Epiblema s cudderiana. Both species increased the proportion of unsaturated fatty acids during the winter. Whereas total lipid content did not change i n Eurosta solidaginis, a decrease in total lipids over the winter in E piblema scudderiana suggested the use of fat reserves to maintain basa l metabolism. Changes in the activities of enzymes of fat oxidation co rrelated with these observations in Eurosta solidaginis: hydroxyacyl-C oA dehydrogenase, carnitine-palmitoyl transferase, and acetoacetyl-CoA thiolase activities all decreased during overwintering. In Epiblema s cudderiana the same activities were constant decreased, or increased. These activities were, however, higher in the fat-oxidizing, freeze-av oiding species than in the freeze-tolerant larvae. Lipid content in Ep iblema scudderiana increased again by early, spring, possibly, indicat ing this pool as the fate of carbon derived from the spring clearance of the cryoprotectant glycerol pool. Decreased activities of malic enz yme and ATP-citrate lyase suggested decreased potential for fatty acid synthesis in both species over the winter, consistent with the cessat ion of feeding in the fall. The potential for ketone body metabolism, measured as the activity of beta-hydroxybutyrate dehydrogenase, increa sed greatly in both species during overwintering; however, levels of b eta-hydroxybutyrate remained less than 0.35 mu mol/g wet mass througho ut the study period. These data indicate that changes to storage lipid profiles in order to maintain fluidity and to lipid-metabolizing enzy me activities may play important roles in insect cold hardiness.