Evaluation of the potential insecticide activity of Tagetes minuta (Asteraceae) essential oil against the head lice Pediculus humanus capitis (Phthiraptera: Pediculidae)

Pediculosis is a worldwide head infestation caused by Pediculus humanus capitis De Geer. Resistance to chemical active ingredients shows the importance of new approaches for head lice control. The aim of the present work was to evaluate the potential insecticide activity of the medicinal plant Tagetes minuta (Asteraceae) against P. humanus capitis as well as to investigate histopathological aspects to find the target sites of the botanical extract in the insect. Lice were collected from heads of infested children 6-12 years old from Marilia, Sao Paulo State, Brazil. All the procedures from the collection to the insecticide evaluation were done according to the World Health Organization protocols. Batches of 10 lice each were released onto a clean piece of filter paper in a petri dish. A 100 ppm concentration of essential oil impregnated filter papers were made by dropping 0.1 ml of T. minuta essential oil. Petri dishes were placed in a rearing chamber (30degreesC and 70% relative humidity) in the dark. Eight replicates were used for treatment and two replicates for control batches. The Median Lethal Time (LT50) was 16.4 +/- 1.62 min. For histophatological investigation, twenty treated and untreated lice were fixed in 10% solution of formalin for 24h and processed according to classical histology techniques. Examined cross sections of treated adults showed disassembly of actin and myosin filaments arrangement when compared to untreated adults. This aspect allied to the LT 50 obtained suggests a toxic action of the T. minuta essential oil.