Head lice are more attracted to blends than to isolated compounds

ADJEMIAN, VICTOR; F GALASSI; M PICOLLO; P GONZALEZ AUDINO

Congreso; 7th International Conference on Phthiraptera (ICP 7); 2023

Pediculushumanus capitis is an obligate bloodsucking ectoparasite of thehuman scalp. Pediculosis affects mainly kids at scholar age.Chemical cues are involved in the head lice-human interaction. Recent studies of our laboratory demonstrated that adulthead lice responded to host chemical stimuli (odor). Moreover, these studiesdemonstrated that head lice were highly attracted to a human scalp compound extract.More recently, we demonstrated that head lice recognize and prefer the wholeodor (highly and moderately volatile emanations) of the human head over thewhole odor of other parts of the human body. In this work, we identified the main components from human scalp extractby CG-MS analysis. The major components were squalene (also presented in otherparts of the human skin), tetradecanoic acid, palmitoleic acid, palmitic acidand oleic acid. Attraction to these individual and mixed components at naturalconcentrations was tested in an experimental arena, composed by 55 mm diameter discsof Whatman #1 filter paper divided in two arenas (control and treated). The arena was enclosed with a5 cm circular glass ring to prevent insect escapes and kept at 21 lux light and30°C temperature.A 1.5 cm2 filterpaper square impregnated with the test sample was placed on one half of thearena and an untreated filter paper on the other. One insect was gently placedin the center of the arena and allowed to walk freely for 180 seconds. Itsmovements were observed by an infrared camera and recorded by a digitalvideo.The control arena consisted of the divided circular filter paper with oneuntreated filter paper square on each side. Noattraction of lice was found by the isolated components neither a dilutedmixture (1/5) of the five components. Otherwise, a mixture of these 5 componentsat their natural concentrations showed significant attraction to head lice(p<0,05).Thiswork found that blends from human scalp compounds are attractive to human headlice at natural concentrations. These results suggest that the mixture ofcompounds from the human scalp can orient the insects to their habitat: thehuman head. This work contributes to our understanding of the attractivity ornot of some individuals, and could explain the difference in attractivitybetween young children and adults, and even among susceptible and non-susceptiblechildren.