REPELLENCY OF ESSENTIAL OILS AND THEIR COMPONENTS TO THE HUMAN-BODY LOUSE, PEDICULUS-HUMANUS-HUMANUS

Five essential oils and nine of their components were compared to diet hyl toluamide (DEET) for their repellent activity against the human bo dy louse, Pediculus humanus humanus. The absolute or intrinsic repelle ncy of the compounds was tested by applying the repellent to corduroy patches and comparing them with untreated patches. It was found that t he most effective repellents were DEET and citronella, whose activity lasted at least 29 days. The activity of rosemary lasted at least 18 d ays and that of eucalyptus more than 8 days. The repellent activity of the oil components such as citronellal and geraniol lasted more than 15 and 8 days, respectively. DEET remained effective at a dilution of 1:32, geraniol at 1:8, citronella at 1:4 and rosemary and citronellal at 1:1. The comparative or standard repellency of the candidate repell ents was examined with the aid of a new screening technique using hair s treated with ammonium bicarbonate which is attractive to lice. Using this technique it could be shown that the repellent activity of citro nella and geraniol lasted 2 days and that of rosemary and citronellal for only one day. DEET was active for less than one day. Serial diluti ons of these substances also revealed that citronella was the most pot ent repellent for lice, followed by citronellal, rosemary, geraniol an d DEET. The differences however, were not significant.