E. Zerba

Resistance to insecticides and effect of synergists on permethrin toxicity in Pediculus capitis (Anoplura: Pediculidae) from Buenos Aires.

Abstract 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 β-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.

Partial purification and characterization of Triatoma infestans head acetylcholinesterase

Abstract A cholinesterase (ChE) from the heads of Triatoma infestans was purified partially by sodium deoxycholate solubilization and by ammonium sulphate and acetone fractionation. The enzyme was purified 14 fold with a yield of 78%. The purified ChE was considered to be an acetylcholinesterase (AChE) based on its substrate specificity, its response to selective inhibitors, the pH sensitivity of its hydrolysis of acetylcholine (ACh) and its inhibition by excess substrate. The purified fraction was shown to be free of butyrylcholinesterase and eserine-resistant esterases which were present in crude homogenates. Disc electrophoresis revealed three interconvertible forms of AChE in the purified enzyme. AChE from T. infestans hydrolyses ACh and its thio-analogue (ATC) at higher rates than other choline esters tested. Maximal velocity for the hydrolysis of ACh by this enzyme was shown at pH 3.3 and pH 7.2. With ATC a K m of 3.3 × 10 −5 M was obtained. The organophosphates were shown to be potent inhibitors of the purified AChE.

Insecticidal Activity of Pyrethroids Against Triatoma infestans

The insecticide activity of synthetic pyrethroids to Triatoma infestans was tested by topical application. Deltamethrin, fenpropathrin, bioresmethrin, permethrin, Cypermethrin, d-phenothrin and cyphenothrin showed the highest activity.The susceptibility to poisoning of adult insects by these pyrethroids (except bioresmethrin) was increased by cotreatment with profenofos or with piperonyl butoxide (PBO). Assayed pyrethroids synergized by PBO showed similar general structure.The vinyl cyano pyrethroids showed a knockdown effect with a delayed recovery. During 15 days after intoxication with deltamethrin, insect recovery was observed. Recovery blockage by PBO was observed in cyphenothrin and deltamethrin poisoning at low doses.RésuméL’activité insecticide de pyréthrinoides de synthèse a été essayée par application topique sur Triatoma infestans.Deltaméthrine, fénpropathrine, biorésméthrine, permethrine, cyperméthrine, d-phénothrine et cyphénothrine ont montrée la meilleure activité.La susceptibilité à l’intoxication par ces pyréthrinoides des insectes adultes (avec l’exception de biorésmethrine) a été améliorée en ajoutant le profenofos ou le butoxide de pipéronyl (PBO) dans les traitements. Les pyréthrinoides synergisées par PBO ont montrée une structure chimique similaire. Les vinyl cyano piréthrinoides ont montrée l’effect choc accompagné d’une récupération retardée. Pendant 15 jours aprés l’intoxication avec la deltaméthrine, la récupération des insectes a été obtenue.

Evaluation of the flushing out activity of pyrethroids on Triatoma infestans

Tetramethrin, deltamethrin and Cypermethrin formulated as fumigant tablets or spray(ing) solutions showed flushing out activity on Triatoma infestans. Fumes arising from the tablets were analysed by gas chromatography. The proportion of pyrethroid liberated was between 10 and 20% of the original amount formulated. The flushing out activity shown was dependent on the pyrethroid compound, insect stage and sex. In general deltamethrin proved the most active flushing out agent and Cypermethrin the least active. Maximal activity was shown in the combination of nymphs and tetramethrin. Nymphs of Rhodnius prolixus were only flushed out by deltamethrin. In all cases, deltamethrin and Cypermethrin yielded 100% mortality 7 days after exposure to the pyrethroid fumes, while tetramethrin was not a killing agent.RésuméLa tetraméthrine, la deltaméthrine et la cyperméthrine sont des pyréthrinoides que, formulées soit comme tablette fumigène ou comme solutions (spray), ont expurgé des insectes vecteurs de la maladie de Chagas cachés dans des refuges standards. La concentration des pyréthrinoides libérés des tablettes fumigènes, détecté par la Chromatographie gazeuse, a été 10 à 20% l’original. En plus, il a été observé que l’activité d’expurger les insectes (flushing out) produite par les tablettes fumigènes dépend de: type de pyréthrinoide, espèce d’insecte, stade de développement larvaire et sexe. Les résultats observés indiqueraient que la deltaméthrine a l’effet maximal de “flushing out” tandis que l’activité de la cyperméthrine a démontré être sensiblement inférieur. La tetraméthrine a été la plus active sur le 5 éme stade de Triatoma infestans. D’ail leurs, le 5 éme stade de Rhodnius prolixus a été seulement expurgé par la deltaméthrine. Dans tout les cas, la deltaméthrine et la cyperméthrine ont démontré produire un 100% de mortalité sept jours après l’exposition aux pyréthrinoides, autant que la tetraméthrine a été incapable de produire une sensible mortalité.

Influence of the nutritional state of Triatoma infestans over the insecticidal activity of DDT

1. The influence of nutritional state over topical insecticidal activity of DDT in nymph II of Triatoma infestans was analyzed. 2. DDT LD50 for starved nymph II was more than 150 micrograms/insect, while for nymph II fed to repletion on artificial feeder, was 0.79(0.50-3.13) micrograms/insect and a similar result was obtained for nymph II fed on pigeons (1.09(0.36-7.55) micrograms/insect). 3. A very slow penetration rate of 14C-DDT was obtained in non fed insects (4.4% penetrated 46 hr after treatment) in correspondence with 0% of mortality. 8.5% of 14C-DDT was not recovered from the cuticle 2 hr after topication of fed nymph in correspondence with a 100% of mortality at 24 hr.

The relation between viscosity and penetration of some diethyl p-substituted phenyl phosophorothionates and oil carriers into the cuticle of Triatoma infestans

Abstract The penetration rate of a series of O,O -diethyl p -substituted phenyl phosphorothionates was measured in the conenose bug Triatoma infestans . The influence of some physicochemical parameters was studied. No correlation was observed with π constant but a good linear relationship was obtained with the relative viscosity of the compounds. The penetration rates were also measured with parathion formulated with a series of paraffinic compounds as carriers. An increased penetration of the formulated parathion was observed. A good correlation was established between the viscosity of the oily carriers and the penetration rates in the different formulations. Parathion formulated with an oily vehicle showed an enhanced insecticide effect.

Volatile compounds secreted by Brindley's glands of adult Triatoma infestans: identification and biological activity of previously unidentified compounds

ABSTRACT 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 Brindleys 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 Brindleys gland showed significant responses for 2- and 3-methylbutyl 2-methylpropanoate compared to controls. The mixture of volatiles secreted by excised Brindleysglands 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.

Neurogenesis and occurrence of cholinesterase in eggs of Triatoma infestans

Abstract 1. Eggs of T. infestans incubated at 30°C and 50% r.h. hatched in 15 days. 2. The neurogenesis of T. infestans embryo was studied. The neuroblasts appeared on the third day and the nerve cells on the fourth day. 3. The ontogenesis of cholinesterases was investigated. Activity was first detected on the fourth day coincidentally with the nerve cells appearance. 4. The cholinesterases were characterized as butyrylcholinesterase and acetylcholinesterase. 5. The oxygen analogs of several phosphorothionates insecticides were found to be potent inhibitors of the embryonic acetylcholinesterase.

Cholinesterases and eserine-resistant esterases in the developing embryo of Triatoma infestans and its role as targets for inhibition in the ovicide action of parathion

Abstract 1. Activity of eserine-resistant esterases was found during all the embryonic development of Triatomainfestans. 2. The ontogenesis of esterases and cholinesterases was established by disc gel electrophoresis. Bands were classified as corresponding to aryl plus acetylesterases, carboxyesterases, acetylcholinesterases and butyrylcholinesterases according to the specificity to substrate and its inhibition by paraoxon. 3. Biochemical measurement of esterases after treatment of eggs with parathion showed partial inhibition of eserine-resistant esterases and cholinesterases. Disc gel electrophoresis revealed complete inhibition of bands corresponding to acetylcholinesterases and carboxyesterases and partial inhibition of butyrylcholinesterases. In vitro incubation with 10−5 M paraoxon caused similar inhibition of the esteratic bands. 4. Eggs of T. infestans rolled on 3.2 μg/cm2 of parathion (2 × LC50) developed fully but failed to hatch. A later acetylcholinesterase whose electrophoretic band was strongly visible at the hatching time was suggested as a possible critical target of the delayed ovicide action.

Feeding and mating deterrency by sulfhydryl reagents in Triatoma infestans

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.