CONICET | Buscador de Institutos y Recursos Humanos

Although all studies about insecticide resistance were evaluated on the larval or adult stages of head lice, the development of insecticide resistance in embryos should not be underestimated as a contributive cause of control failures. The aim of this research was to study insecticide resistance in eggs of P. humanus capitis populations whose pyrethroid resistance was demonstrated in postembryonic stages. In addition, the resistance profile to pyrethroid and non-pyrethroid insecticides was comparatively studied in adults and eggs. The head lice (HL) were collected from infested children from elementary schools of Buenos Aires. Three populations were selected according to the permethrin resistance levels assessed in previous studies. A body lice colony was used as susceptible strain. Egg toxicity was evaluated using an immersion technique. Ten late development eggs selected according to external markers were immersed in the insecticide acetonic solutions. Adult and nymph toxicity were done by topical application. Each louse was treated with 0.1 µl of the insecticide solution on the dorsal abdomen. Data from bioassays were subjected to probit method. Eggs of all head lice populations showed high levels of resistance to permethrin (LDR from 884 to 4.876), d-phenothrin (LCR from 173 to 1433) and DDT (LCR from 118.6 to >400), and low resistance to carbaryl. In concordance, adults were high resistance to permethrin (LDR from 16.6 to 265.6), d-phenothrin (LDR from 8.2 to 974.7) and DDT (LDR from 25.3 to >74.6), and low resistance to carbaryl. Results presented here demonstrated high resistance to pyrethroids in eggs of P. humanus capitis, in common with that assessed for nymphs and adults. Additionally, results concerning to the cross-resistance to DDT and carbaryl, suggested that altered site of action and increased oxidative metabolism are cause of insecticide resistance in head lice populations from Argentina

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