RESUMO
The domiciliary presence of Triatoma infestans (Klug) (Hemiptera: Reduviidae) after control interventions was reported in recent years. Toxicological studies showed high levels of resistance to pyrethroids suggesting resistance as one of the main causes of deficient control. The aim of the present study was to develop a protocol to test resistance to deltamethrin in T. infestans collected from the field by discriminate concentration. To evaluate field insects, the effect of age (early vs. later) and nutritional state (starved vs. fed) on the deltamethrin susceptibility of each developmental stage was studied. Topical and insecticide impregnated paper bioassays were used. Using the impregnated paper, the susceptibility to deltamethrin was not affected by the age of the stadium and the nutritional states, and varied with the post-exposure time and with the different developmental stages. A discriminant concentration of deltamethrin (0.36% w/v) impregnated in filter paper was established for all developmental stages. Finally, the methodology and the discriminant concentration were evaluated in the laboratory showing high sensitivity in the discrimination of resistance. The present study developed a methodology of exposure to insecticide impregnated papers and proposes a protocol to test T. infestans in field populations with the aim to detect early evolution of resistance to deltamethrin.
Assuntos
Resistência a Inseticidas , Inseticidas/farmacologia , Nitrilas/farmacologia , Piretrinas/farmacologia , Triatoma/efeitos dos fármacos , Fatores Etários , Animais , Feminino , Masculino , Ninfa/efeitos dos fármacos , Ninfa/crescimento & desenvolvimento , Triatoma/crescimento & desenvolvimentoRESUMO
The effect on locomotor activity, the repellency, and the knock-down produced by 10 monoterpene alcohols were evaluated on first-instar nymphs of Rhodnius prolixus and Triatoma infestans, vectors of Chagas disease. A video tracking technique was used to evaluate locomotor activity and repellency by exposure to papers impregnated with monoterpenes. Eugenol on R. prolixus and (S)-cis-verbenol on T. infestans did not modify the locomotor activity. The remaining monoterpenes produced hyperactivity on both species, although the concentration required was at least a 1,000 times higher than that of deltamethrin (positive control). Carvacrol, eugenol, and geraniol resulted as repellent as N,N-diethyl-m-toluamide (positive control) for both species. A similar result was observed for almost every monoterpene on T. infestans. Knock-down effect was evaluated by exposing the nymphs in closed recipients. The order of increasing toxicity on R. prolixus was (KT50 values in min): geraniol (213.7) < alpha-terpineol (164.5) < linalool (124.2) < carvacrol (111.6) < eugenol (89.8) < thymol (78.9), and on T. infestans: alpha-terpineol (289.8) < eugenol (221.3) < carvacrol (164.2) < linalool (154.9) < thymol (96.7). All monoterpenes were less toxic than the positive control, dichlorvos (3.6 min for R. prolixus and 3.9 min for T. infestans). After 7 h of exposure, (-)-carveol, citronellol, and menthol (on both species) and geraniol (on T. infestans) produced < 50% of knock-down. After these results, it is worthwhile to explore more deeply the potential of these compounds as tools for controlling Chagas disease vectors.
Assuntos
Controle de Insetos/métodos , Repelentes de Insetos/farmacologia , Monoterpenos/farmacologia , Atividade Motora/efeitos dos fármacos , Rhodnius/efeitos dos fármacos , Triatoma/efeitos dos fármacos , Álcoois/farmacologia , Animais , Ninfa/efeitos dos fármacos , Ninfa/fisiologia , Rhodnius/crescimento & desenvolvimento , Rhodnius/fisiologia , Especificidade da Espécie , Triatoma/crescimento & desenvolvimento , Triatoma/fisiologia , Gravação de VideoteipeRESUMO
The aim of this study was to evaluate the fumigant and repellent activity of five essential oils (from eucalyptus, geranium, lavender, mint, and orange oil) and seven monoterpenes (eucalyptol, geraniol, limonene, linalool, menthone, linalyl acetate, and menthyl acetate) on first-instar nymphs of the bloodsucking bug Rhodnius prolixus Stahl (vector of Chagas disease in several Latin American countries). Fumigant activity was evaluated by exposing the nymphs to the vapors emitted by 100 microl of essential oil or monoterpene in a closed recipient. The knockdown time 50% (KT50) for eucalyptus essential oil was 215.6 min (seven times less toxic than dichlorvos, a volatile organophosphorus insecticide used as a positive control). The remaining essential oils showed a poor fumigant activity: < 50% of nymphs were knocked down after 540 min of exposure. The KT50 values for monoterpenes, expressed in minutes, were as follows: 117.2 (eucalyptol), 408.7 (linalool), 474.0 (menthone), and 484.2 (limonene). Eucalyptol was 3.5 times less toxic than dichlorvos. No affected nymphs were observed after 540 min of exposure to geraniol, linalyl acetate, or menthyl acetate. Repellency was quantified using a video tracking system. Two concentrations of essential oils or monoterpenes were studied (40 and 400 microg/cm2). Only mint and lavender essential oils produced a light repellent effect at 400 microg/cm2. Geraniol and menthyl acetate produced a repellent effect at both tested concentrations and menthone only elicited an effect at 400 microg/cm2. In all cases, the repellent effect was lesser than that produced by the broad-spectrum insect repellent N,N-diethyl-3-methylbenzamide (DEET).
Assuntos
Fumigação , Controle de Insetos/métodos , Inseticidas , Monoterpenos , Óleos Voláteis , Óleos de Plantas , Rhodnius , Animais , Ninfa , Plantas/química , Rhodnius/crescimento & desenvolvimentoRESUMO
The medical and veterinary pest Musca domestica L. has developed resistance to most insecticides used against it. For this reason, there is a constant search for new alternative control tools. The aims of this study were (1) to evaluate the toxicological effects caused by the fumigant activity and the topical application of five essential oils and five monoterpenes in M. domestica adult males and (2) to study the variation of the fumigant activity of the essential oils and monoterpenes according to the solvent used (acetone or a silicone base). Houses flies were exposed to vapors delivered by filter paper treated with 200 microl of essential oil or monoterpene (10%) in acetone or a silicone base. The knockdown time 50% (KT50) values obtained for essential oils (expressed in minutes) were 3.3 (eucalyptus); 10.1 (orange); 10.4 (mint); 10.9 (lavender); and 17.7 (geranium). The KT50 values obtained for monoterpenes (expressed in minutes) were 2.3 (eucalyptol); 7.5 (limonene); 7.6 (linalool); 19.0 (menthone); and 22.6 (menthyl acetate). In all cases, a delay in the onset of poisoning symptoms was observed when a silicone base vehicle was used. When topically applied, the lethal dose 50% (LD50) values for essential oils (expressed in micrograms of oil/insect) were 0.07 (geranium); 0.09 (mint); 0.13 (lavender); 0.14 (eucalyptus); and 0.16 (orange). The LD50 values for monoterpenes (expressed in micrograms of monoterpene/insect) were 0.04 (linalool); 0.09 (menthyl acetate); 0.10 (limonene); 0.11 (menthone); and 0.13 (eucalyptol). These results suggest that the studied essential oils and monoterpenes are potential tools for controlling M. domestica.
Assuntos
Moscas Domésticas/efeitos dos fármacos , Controle de Insetos/métodos , Monoterpenos/toxicidade , Óleos Voláteis/toxicidade , Animais , Dose Letal Mediana , Monoterpenos/administração & dosagem , Óleos Voláteis/administração & dosagem , Fatores de Tempo , VolatilizaçãoRESUMO
The repetitive and inadequate application of pediculicidal products frequently results in the development of resistance to these compounds. Essential oils are a promising alternative to synthetic insecticides, although their mode of action remains to be explored. It has been proposed that one possible target of the essential oils is the inhibition of acetylcholinesterase (AChE). The role of monoterpenoids as possible AChE inhibitors and their relationship with the toxicity was investigated both in vitro and in vivo. Inhibition of electric eel AChE activity showed that the most effective inhibitor was 1,8-cineole with IC(50) 6 x 10(-3) M. The inhibition of AChE activity of head louse homogenate by 1,8-cineole showed IC(50) 7.7 x 10(-2) M. The intoxication symptoms of head lice exposed to vapors of 1,8-cineole was recorded before the in vivo head louse AChE inhibition assay. No correlation was found between neurotoxic symptoms and inhibition of AChE activity.
Assuntos
Inibidores da Colinesterase/farmacologia , Cicloexanóis/farmacologia , Inseticidas/farmacologia , Monoterpenos/farmacologia , Ftirápteros/efeitos dos fármacos , Acetilcolinesterase/metabolismo , Animais , Inibidores da Colinesterase/química , Cicloexanóis/química , Relação Dose-Resposta a Droga , Electrophorus , Eucaliptol , Inseticidas/química , Monoterpenos/química , Fatores de TempoRESUMO
Volatile emissions of adult male Triatoma infestans were collected on non-polar SPME fibers and analyzed by gas chromatography linked to a mass spectrometer. A complex mixture of 16 short-chain esters and acids were identified. The composition of short-chain aliphatic acids (ethanoic to nonanoic acids) was similar to previously reported results. The most abundant aliphatic acid was 2-methylpropanoic acid, constituting 18% of the total volatile content. Also abundant were the esters 2- and 3-methylbutyl 2-methylpropanoate, which constituted 30% and 22%, respectively, of the total volatile content. A similar pattern of compounds was observed in the volatiles secreted by dissected male Brindley's glands; however, in this case, 2- and 3-methylbutan-1-ol were detected which were not found in live insect volatile emissions. Large variability in volatile composition was also observed among the glands excised from different insects. Electroantennographic (EAG) evaluation of the components of Brindley's gland showed significant responses for 2- and 3-methylbutyl 2-methylpropanoate compared to controls. The mixture of volatiles secreted by excised Brindley's glands and the isolated 2- and 3-methylbutyl 2-methylpropanoate had repellent effects on both male and female T. infestans, possibly associated with a defensive strategy.
Assuntos
Feromônios/análise , Glândulas Odoríferas/metabolismo , Triatoma/metabolismo , Animais , Feminino , Cromatografia Gasosa-Espectrometria de Massas , Masculino , Feromônios/química , Feromônios/metabolismo , VolatilizaçãoRESUMO
Monoterpenes are the main components of essential oils. Some members of this chemical family present insecticidal activity. Triatoma infestans (Klug) is the main vector of Chagas disease in Argentina, Bolivia, Paraguay, and Perú. The objective of this work was to evaluate the effect of six monoterpenes (1,8-cineole, eugenol, linalool, menthol, α-terpineol, and thymol) on the locomotor and flushing out activity of T. infestans. A video tracking technique was used to evaluate the locomotor activity of nymphs exposed to different concentrations of these chemicals applied as films on filter paper. Papers treated with acetone alone were used as negative controls, while solutions of tetramethrin were applied as positive controls. Only linalool and menthol produced hyperactivation. Flushing out was assessed under laboratory conditions using a standardized aerosolization method. All monoterpenes were applied at 1.5 g/m3. 1,8-Cineole, α-terpineol, and thymol flushed out 10% or less nymphs. The average flushing out produced by eugenol was 36.7%. Values of median flushing out time (FT50) could only be calculated for linalool and menthol (16.67 and 42.98 min, respectively). The FT50 value for the positive control tetramethrin (applied at 0.006 g/m3) was 8.29 min. Following these results, the flushing out activity of a mixture of linalool and eugenol was evaluated. The FT50 of this 2:1 linalool:eugenol mixture was 40.73 min. Finally, flushing out assays performed in semifield conditions showed similar results to those obtained at the laboratory.
Assuntos
Controle de Insetos , Inseticidas , Monoterpenos , Piretrinas , Triatoma , Monoterpenos Acíclicos , Animais , Eugenol , Ninfa/crescimento & desenvolvimento , Triatoma/crescimento & desenvolvimentoRESUMO
The insecticidal activity of spinosad was evaluated against susceptible and permethrin-resistant human lice. In a permethrin-susceptible strain of the body louse, Pediculus humanus humanus L. (Anoplura: Pediculidae), the toxicity of spinosad was similar to that established for permethrin, with an LD50 value of 1.2 ng/insect and 2.4 ng/insect, respectively. Topical application of spinosad to populations of permethrin-resistant head louse, Pediculus humanus capitis De Geer (Anoplura: Pediculidae), showed that susceptibility to spinosad was independent of resistance to permethrin. The effectiveness of spinosad against human lice and the low mammalian toxicity reported in the literature suggest that spinosad could be useful for the management of permethrin-resistant human lice.
Assuntos
Resistência a Inseticidas , Macrolídeos/farmacologia , Pediculus/efeitos dos fármacos , Permetrina , Animais , Argentina , Combinação de Medicamentos , Dose Letal MedianaRESUMO
We studied the profile of permethrin resistance in populations of head lice infesting children 6-12 yr old in schools and their homes in and around Buenos Aires, Argentina. Five permethrin-resistant populations with different levels of resistance were collected: Hogar Loyola (HL), Republica de Turquia (RT), Hogar Mitre (HM), Guardia de Honor (GH), and Ricardo Guiraldes (RG). One susceptible population, Bandera Argentina (BA), also was collected. Their level of resistance was evaluated, and results showed resistance ratios of 13 for HL, 16 for RT, 22 for HM, 61 for GH, and 69 for RG. To elucidate the possible involvement of the cytochrome P450 monooxygenase system in conferring permethrin resistance, ethoxycoumarin-O-deethylase (ECOD) activity was measured in abdomens of individual third instars and adults by using a fluorometric assay. The ECOD activity was lower in the susceptible BA population (4.7 ng per louse) than in the resistant ones (13.7 ng per louse for RG, 12.3 ng per louse for GH, 8.6 ng per louse for RT, and 8.2 ng per louse for HL). ECOD activity was significantly correlated with the level of resistance in the field populations (r = 0.97, P = 0.0009), suggesting a role for cytochrome monooxygenase P450 system in permethrin resistance by head louse, Pediculus humanus capitis De Geer.
Assuntos
O-Dealquilase 7-Alcoxicumarina/metabolismo , Resistência a Inseticidas , Pediculus/enzimologia , Permetrina , Animais , Argentina , Criança , Humanos , Infestações por Piolhos/tratamento farmacológicoRESUMO
We report here the identification and behavioral activity of volatile compounds emitted by male Platypus mutatus (=sulcatus) Chapuis while boring galleries in living poplar, Populus deltoides Marshall, trees. Headspace analysis using solid phase microextraction techniques showed the presence of 6-methyl-5-hepten-2-ol (sulcatol) and 6-methyl-5-hepten-2-one (sulcatone). Only one enantiomer of sulcatol, retusol, was found to be part of the volatile emission. Behavioral assays showed that females are more attracted than males to galleries with boring males inside. Both sulcatol and sulcatone elicited electroantennographic responses by female P. mutatus. Furthermore, behavioral bioassays showed that both sulcatol and sulcatone elicit behaviorally attractive responses by females. These results suggest that male P. mutatus releases a sex pheromone composed mainly of retusol and sulcatone.
Assuntos
Comportamento Animal , Besouros/fisiologia , Odorantes/análise , Animais , Feminino , Cetonas/análise , Masculino , Octanóis/análiseRESUMO
The behavioural responses of the haematophagous bug Triatoma infestans towards some previously identified components of its faeces: 4-methylquinazoline, 2,4- dimethylquinazoline and their mixtures were evaluated using a video tracking system. Fifth instar nymphs and females but not males were significantly attracted to polyethylene glycol formulations of 4-methyl + 2,4-dimethylquinazoline (50 microg each). Fifth instar nymphs were also attracted to 4-methylquinazoline alone (50 microg) but females were only attracted by the mixture of both methyl quinazolines (50 microg each). Syntheses of both methyl quinazolines were carried out starting from 2-aminoacetophenone by modifying the conditions of reported procedures.
Assuntos
Comportamento Animal/efeitos dos fármacos , Quinazolinas/farmacologia , Triatoma/efeitos dos fármacos , Animais , Bioensaio , Feminino , Masculino , Ninfa/efeitos dos fármacos , Quinazolinas/químicaRESUMO
In old compared with young animals, muscle mass is decreased by 30% to 40%, and maximum force and power are decreased to an even greater extent. The age-related declines in muscle mass and muscle function are similar to those that occur with decreased physical activity. Despite the similarities, we conclude that the losses in muscle mass, force, and power are not due solely to old animals being less active, but rather accrue from intrinsic age-related changes in muscles and in muscle fibers that appear to be immutable and irreversible. The intrinsic changes are associated with denervation of fast fatigable fibers and motor units and motor unit remodeling, which may be initiated by contraction-induced injury. The mechanisms remain unresolved for the weakness, the fatigability, the high susceptibility to contraction-induced injury, and the impaired recovery from injury demonstrated by the skeletal muscles of old animals.
Assuntos
Envelhecimento/fisiologia , Contração Muscular , Debilidade Muscular/fisiopatologia , Músculo Esquelético/fisiopatologia , Atrofia Muscular/fisiopatologia , Adaptação Fisiológica , Animais , Composição Corporal/fisiologia , Atividade Motora/fisiologia , Fadiga Muscular , Fibras Musculares de Contração Rápida/fisiologia , Fibras Musculares Esqueléticas/fisiologia , Músculo Esquelético/inervação , Degeneração NeuralRESUMO
The hyperactivity (an increase in locomotor activity) and repellency produced by eight pyrethroids, applied as films on filter paper, were evaluated on fifth instar nymphs of Triatoma infestans (Hemiptera: Reduviidae) using a video tracking technique. All the pyrethroids studied produced hyperactivity. As a trend, hyperactivity produced by cyanopyrethroids was higher than that produced by non-cyanopyrethroids. Hyperactivity was not observed when nymphs were pretreated with the sulphydryl reagent N-ethylmaleimide before exposure to the pyrethroids. The eight pyrethroids failed to produce repellency. No repellency was also observed for the flowable formulation of deltamethrin at the concentration recommended for T. infestans control.
Assuntos
Hipercinese/induzido quimicamente , Inseticidas/farmacologia , Piretrinas/farmacologia , Triatoma/efeitos dos fármacos , Animais , Comportamento Animal/efeitos dos fármacos , Etilmaleimida/farmacologia , Processamento de Imagem Assistida por Computador , Gravação de VideoteipeRESUMO
Topical application of different sulfhydryl (SH) reagents in acetone solution resulted in a deterrence of the feeding activity of Triatoma infestans nymph V. The ED50 for topical application of N-ethylmaleimide (NEM), the more active compound assayed, was 8.9 micrograms/insect. This effect showed a dose-dependent reversibility. We also observed feeding deterrency when a gauze cloth impregnated with NEM was located between the food source and the nymphs. After topical NEM treatment, mating deterrency was assessed by counting spermatophores dropped and eggs laid. When a population of adult insects, nymphal stages and eggs was reared in a cage containing filter papers treated with 0.4 mg/cm2 of NEM, a significant decrease of population density was seen after 200 days of exposure. Weekly replacement of filter papers impregnated with 0.13 mg/cm2 NEM for a period of one year enabled population control to be maintained. Antifeeding and antimating effects of NEM in Triatoma infestans and the resulting population control could be attributed to a chemoreceptor blockage produced by SH reagents.
Assuntos
Comportamento Alimentar/efeitos dos fármacos , Insetos Vetores/efeitos dos fármacos , Comportamento Sexual Animal/efeitos dos fármacos , Compostos de Sulfidrila/farmacologia , Triatoma/efeitos dos fármacos , Animais , Etilmaleimida/farmacologia , Feminino , Insetos Vetores/crescimento & desenvolvimento , Insetos Vetores/fisiologia , Masculino , Densidade Demográfica , Triatoma/crescimento & desenvolvimento , Triatoma/fisiologiaRESUMO
We evaluated the toxicity of deltamethrin and cis-permethrin at 3 temperatures on instars of Triatoma infestans (Klug). After treatment, temperature had an important effect on LD50s of both insecticides, which tended to decrease when temperature decreased. However, the effect of temperature on LT50s was small. Cis-permethrin was slightly more lethal than deltamethrin only at 26 degrees C. Lethal action of deltamethrin was faster than cis-permethrin at all temperatures assayed. The toxicity of both pyrethroids was affected by the age and the nutritional state of the nymphs. We evaluated sublethal effects on blood meal ingestion and moulting. Only deltamethrin yielded a substantial decrease in the number of moulted nymphs.
Assuntos
Inseticidas , Piretrinas , Triatoma , Animais , Nitrilas , Fenômenos Fisiológicos da Nutrição , Ninfa , Permetrina , TemperaturaRESUMO
We found that feeding behavior of Triatoma infestans (Klug) 5th-instar nymphs was blocked by topical application of the cis-isomers of methyl esters of N-substituted maleamic acids, synthesized in our laboratory. The antifeeding effect of these compounds was determined by exposing 5th-instar nymphs to impregnated filter papers. The greatest antifeeding effect was observed for the shortest alkyl chain of cis-N-substituted methyl maleamate (EC50: 2.47 micrograms/cm2 when the substituent was ethyl and 65.1 micrograms/cm2 when it was octil). The continuous exposure of a T. infestans population to ethyl, buthyl, heptil, or octil maleamates at an initial concentration of 0.1 mg/cm2 produced significant (P < 0.05) decrease in the development of the exposed populations ranging from 220 to 400 d for the different maleamates assayed. These results suggest the antifeeding maleamates as a specific alternative method of T. infestans control.
Assuntos
Comportamento Alimentar , Maleatos , Triatominae , AnimaisRESUMO
The effectiveness of 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, and 1-dodecanol was evaluated by immersion method against susceptible and permethrin-resistant head lice, Pediculus humanus capitis De Geer, from Buenos Aires, Argentina. All the tested alcohols showed knockdown effect at 10 min and mortality 18 h after treatment. The highest activity was found for the 1-dodecanol (KC50 2.55%, LC50 2.28%) and the lowest for 1-octanol (KC50 8%, LC50 4.46%). The toxicity to the head lice systematically increased with the increase in carbon atoms in the n-aliphatic alcohol moiety, and with the octanol:water coefficient (r2 = 0.94). The pediculicidal activity of 1-dodecanol was not correlated with resistance to permethrin, because no significant difference was observed between toxicity parameters in the susceptible (MAR) and the permethrin-resistant populations which had different resistant levels (RR 5.77 x for E49 population, RR 9.5 x for HL population and RR > 35.3 x for GH population). The pediculicidal effect of aliphatic alcohols demonstrated in this study and the lack of correlation with the permethrin resistance may prove to have a practical value for use in susceptible and permethrin-resistant head lice control.
Assuntos
Álcoois/farmacologia , Controle de Insetos/métodos , Pediculus/efeitos dos fármacos , Permetrina , Dermatoses do Couro Cabeludo/parasitologia , Animais , Dodecanol/farmacologia , Álcoois Graxos/farmacologia , Resistência a Inseticidas , Octanóis/farmacologia , Dermatoses do Couro Cabeludo/prevenção & controleRESUMO
Permethrin-resistant colonies of Pediculus capitis (De Geer) from Buenos Aires were used to establish a resistance profile and to examine resistance mechanisms. All permethrin-resistant head lice (resistance ratio from 52.8 to > 88.7) were also resistant to d-phenothrin (resistance ratio from 40.86 to > 48.39) and deltamethrin (resistance ratio from 16.24 to 38.06). No cross-resistance to carbaryl was found in any of the pyrethroid-resistant P. capitis tested. Otherwise, all resistant colonies showed low to high levels of resistance to beta-cypermethrin. This pyrethroid had never been applied as a pediculicide in Argentina; however, the high level of resistance found in these permethrin-resistant colonies (resistance ratio from 9.74 to 50.97) demonstrated that pyrethroid cross-resistance occurred to this novel insecticide. Treatment with piperonyl butoxide (PBO) or triphenylphosphate (TPP) significantly decreased the toxicity of permethrin in the four colonies tested. The esterase inhibitor TPP produced lower enhancement of toxicity than the multifunction oxidase inhibitor PBO in the colonies having the highest resistance levels. Results presented here concerning the cross-resistance profile and synergism by enzyme inhibitors in permethrin-resistant head lice demonstrated that enhanced metabolism was involved in the pyrethroid resistance. However, the substantial degree of resistance that remained after synergism suggested the presence of another resistance mechanism. Cross-resistance to pyrethroid and susceptibility to the carbamate carbaryl suggested a common action mechanism.
Assuntos
Inseticidas , Pediculus , Piretrinas , Animais , Argentina , Carbaril , Criança , Dietilexilftalato , Resistência a Medicamentos , Sinergismo Farmacológico , Humanos , Infestações por Piolhos , Organofosfatos , Permetrina , Butóxido de Piperonila , População UrbanaRESUMO
The susceptibility of local head lice to permethrin, sumithrin, deltamethrin, and carbaryl was determined by laboratory bioassays in field-collected colonies. Head lice collected from the infested heads of children 6-12 yr old were tested within 3 h of collection. The longest survival of control insects in the laboratory was obtained by keeping them in the dark at 18 degrees C and 70-80% RH. The base line susceptibility data obtained for insects collected from children not treated for lice, the reference colony, showed that deltamethrin caused the highest mortality of the insecticides tested (LC50, 0.06%). Permethrin, sumithrin, and carbaryl showed no significant difference in mortality (superposition of confidence intervals), being 10 times lower than that caused by deltamethrin. All field-collected lice required a higher LC50 of permethrin than the reference colony. Resistance levels varied from 3 to > 100 for colonies that were taken from children treated with anti-lice products. Lice colonies with permethrin resistance showed resistance to sumithrin and deltamethrin, but resistance was not observed to the carbamate carbaryl.
Assuntos
Resistência a Inseticidas , Inseticidas/toxicidade , Infestações por Piolhos/parasitologia , Pediculus , Animais , Bioensaio , Carbaril/toxicidade , Criança , Geografia , Humanos , Nitrilas , Permetrina , Piretrinas/toxicidadeRESUMO
Permethrin has been used extensively for control of Pediculus humanus capitis De Geer (Anoplura: Pediculidae) in Argentina since 1990, resulting in the development of resistance to this and other pyrethroids. This resistance was first detected in some field populations in 1997. A survey for resistance in Buenos Aires in 2001 revealed significant resistance levels in lice on children at 24 of 26 (92.3%) schools. When compared with a previously unexposed reference population, resistance ratios (RRs) obtained by exposing the insects to filter papers impregnated with permethrin ranged from 2 to 60 in 10 (39%) of the schools. RRs in the remaining 14 (61%) populations were too great to not be measured with the filter paper method (RR > 88.7). As an alternative, we used topical applications of 0.1 microl of acetone solution of permethrin on the dorsal abdomen of adults and third instars. This topical method, which has not been previously reported for head lice, was capable of quantifying higher levels of resistance. Highly resistant populations had RRs from 162.5 to 655.2. When applied to populations with low and intermediate levels of resistance, results from the filter paper and topical application methods were highly correlated, and RRs from topical application were higher than those from the filter paper method. Results from the combination of the two methods indicated that head lice among Buenos Aries school children are highly resistant to permethrin, and the resistance is widespread.