We report on the presence of phospholipase A 2 activity in whole larva and midguts of the yellow fever mosquito Aedes aegypti. Phospholipase A 2 is responsible for hydrolyzing fatty acids from the sn-2 position of dietary phospholipids to release essential fatty acids for normal larval and adult growth. In contrast to the mammalian digestive phospholipase A 2 background, the Ae. aegypti phospholipase A 2 was Ca 2+-independent. We further characterized the mosquito midgut phospholipase A 2 by altering the reaction conditions including incubation time, protein concentrations, pH and temperature. The site-specific PLA 2 inhibitor oleyloxyethylphosphorylcholine failed to inhibit the enzyme at concentrations up to 5000 μM. We found that the phospholipase A 2 activity was consistently high throughout the fourth instar, but fell to very low levels on the first day of pupation which is a non-feeding stage. The enzyme is regulated with respect to feeding activity because fasting and re-feeding modified the larval digestive PLA 2 activity.