Ovicidal and adulticidal activities of Cinnamomum zeylanicum bark essential oil compounds and related compounds against Pediculus humanus capitis (Anoplura: Pediculicidae)

The toxicity of cinnamon, Cinnamomum zeylanicum, bark essential oil compounds against eggs and adult females of human head louse, Pediculus humanus capitis, was examined using direct contact and vapour phase toxicity bioassays and compared with the lethal activity of their related compounds, benzyl alcohol, cinnamic acid, cinnamyl acetate, 4-hydroxybenzaldehyde and salicylaldehyde, as well as two widely used pediculicides, d-phenothrin and pyrethrum. In a filter-paper contact toxicity bioassay with female lice at 0.25 mg/cm², benzaldehyde was 29- and 27-fold more toxic than pyrethrum and d-phenothrin, respectively, as judged by median lethal time (LT₅₀) values. Salicylaldehyde was nine and eight times more active than pyrethrum and d-phenothrin, respectively. Pediculicidal activity of linalool was comparable with that of d-phenothrin and pyrethrum. Cinnamomum bark essential oil was slightly less effective than either d-phenothrin or pyrethrum. Benzyl alcohol and (E)-cinnamaldehyde exhibited moderate pediculicidal activity. After 24 h of exposure, no hatching was observed with 0.063 mg/cm² salicylaldehyde, 0.125 mg/cm² benzaldehyde, 0.5 mg/cm² Cinnamomum bark essential oil, 1.0 mg/cm² (E)-cinnamaldehyde, and 1.0 mg/cm² benzyl cinnamate. Little or no ovicidal activity was observed with d-phenothrin or pyrethrum. In vapour phase toxicity tests with female lice, benzaldehyde and salicylaldehyde were much more effective in closed containers than in open ones, indicating that the mode of delivery of these compounds was largely due to action in the vapour phase. Neither d-phenothrin nor pyrethrum exhibited fumigant toxicity. Cinnamomum bark essential oil and test compounds described merit further study as potential pediculicides or ovicides for the control of P. h. capitis.     

How long do louse eggs take to hatch? A possible answer to an age‐old riddle

There are no rigorous data on how long eggs of the head louse, Pediculus capitis (Phthiraptera: Pediculidae), take to hatch. Pediculicide users often report re‐infestations after apparently successful treatments in the absence of infective contacts. This study aimed to resolve the question of whether some louse eggs hatch after the completion of treatment, thereby giving rise to a new infestation. Data were extracted from the records of lice collected after treatments in 20 clinical intervention trials. All datasets were eliminated except those in which only newly hatched louse nymphs were found prior to the final assessment. This excluded the possibility that new eggs were laid after the first treatment and thus any young lice found must have originated from eggs laid before the start of treatment. This identified 23 of 1895 (1.2%) records with evidence of louse nymphs emerging at 13 days or more after the first treatment, 3–6 days longer than previous estimates. Current treatment regimens for pediculicides of two applications 7–10 days apart appear inadequate, which may explain continuing infestation in the community. Therefore, it is suggested that a revised approach using three treatments applied at intervals of 1 week should prevent the survival of any nymphs and their development into a new generation of adults.