Effect of altered phospholipid head groups on the distribution of cholesterol in the housefly ( Musca domestica) larvae

Abstract

The phospholipid composition of larvae of the housefly, Musca domestica, was altered by rearing them on defined diets containing adequate choline, no added choline, and choline plus 2-aminobutan-1-ol (2-AB-1-ol). The distribution of sterols in various tissues of insects with altered phospholipid head groups was examined and the sterol content related to the phospholipid and protein content. The results indicate that addition of 2-AB-1-ol to the control diets did not produce any significant changes in the sterol content (nmole/tissue) of various larval tissues. However, choline deficiency affected the growth of larvae. The composite gut fraction (gut, salivary glands and Malpighian tubules) of choline deficient insects contained a lower ratio of free sterol to protein or phospholipid than was found in the other two groups. The addition of graded amounts of choline to the deficient larval diets caused the molar ratio of sterol to phospholipid of the composite gut fraction to increase while that of the haemolymph fell in a complementary manner until approx. 1.40 μmole choline/g of casein had been added to the diets. The dietary regimes studied did not affect significantly the distribution of total sterols between polar, esterified and free sterols in the insect. The observed results following modification of phospholipid head groups in the tissues of insects are discussed.