Head louse infestation is difficult to control because of increasing lice resistance to synthetic pediculicidal drugs.

To test the activity of extract and oil obtained from fruits of Melia azedarach L. against the head louse Pediculus humanus capitis.

A filter paper diffusion bioassay was carried out in order to determine the pediculicidal and ovicidal activity of extract and oil from M azedarach L. fruits.

Both vegetable products, tested either individually or in combinations, showed high levels of mortality on adult lice, with values ranging between 62.9% and 96.5%. The highest mortality rate was obtained with a combination of 20% ripe fruit extract with 10% ripe fruit oil. A formulation made with both extract and oil at 10% plus the addition of emulsifier and preserving agents showed 92.3% pediculicidal activity. The products were also successful in delaying or inhibiting nymph emergence, with the formulation being the most effective, with a complete inhibition of emergence.

Because adult lice are sensitive to starvation and therefore control mortalities are often higher than 20% in tests with field specimens, the results may not reflect the direct effect of the extract.

These results demonstrate the possibility of using Melia products for controlling head lice, which are difficult to control because of their resistance to the currently used anti-louse agents.