Tsetse Flies and Mammals Share a Milk Enzyme Geoffrey Attardo Production of the enzyme could be manipulated to help reduce flies that spread diseases. Female tsetse flies produce only one egg at a time. The larva hatches in the mother's uterus, and she feeds it with a milklike substance that she produces. Now, researchers report that tsetse milk contains an enzyme called sphingomyelinase, or sMase, that is also important in mammalian lactation. And that means the flies can be used to help study issues in human lactation, said Joshua Benoit, an entomologist at Yale University who was involved with the research. He and his colleagues report their findings in the journal The Biology of Reproduction. In humans, for example, sMase deficiencies can cause Niemann-Pick disease, a neurological disorder that can be fatal in young children. Then there is sleeping sickness (and a related animal disease, nagana), which is caused by parasites transmitted by the bite of the tsetse fly. Sleeping sickness can be fatal if it is not treated early, and there is no vaccine for the disease. The researchers believe that manipulating the production of the lactation enzyme in female flies could aid in reducing their population. This might be done by chemical spraying of the animals that the flies feed on, Dr. Benoit said.