Triatoma infestans (Klug, 1834) (Hemiptera, Reduviidae) is the main vector of Chagas disease in the southern cone South America. Chemical control to the vectors appears to be the best option to reduce the incidence of the disease. However, since 2002, high resistance to insecticides that correlated with field control failures was detected in T. infestans from Argentina and Bolivia. In this paper, we analyzed three T. infestans populations whose pyrethroid-resistance had been recently detected, and we defined at least three resistant profiles according to the toxicological and biochemical characteristics of the studied resistant populations. The resistance profiles were identified as Ti-R1, Ti-R2, and Ti-R3, corresponding to the Argentinean Acambuco, and the Bolivians Entre Ríos and Mataral. Ti-R1 exhibited nymphs and eggs with medium resistance level to deltamethrin (RR = 32.5 and 28.6; respectively). Pyrethroid-esterases played a relevant role in deltamethrin resistance. Ti-R2 exhibited nymphs with high resistance to deltamethrin (RR = 173.8) and low resistance to fipronil (RR = 12.4). Pyrethroid-esterases were involved in resistance. Moreover, eggs showed medium resistance level to deltamethrin (RR = 39.1). Ti-R3 had nymphs with low resistance to deltamethrin (RR = 17.4), and medium resistance to fipronil (RR = 66.8). Pyrethroid-esterases showed increased activity, and eggs possessed low resistance to deltamethrin (RR = 8.4). The characterization of the resistance to pyrethroid in these T. infestans populations from Argentina and Bolivia do not permit the generalization of three forms of resistance profile. So far as we appear to know, the forms of mechanisms and their frequencies reported here are selected independently, so additional sites might well show additional combinations of resistance mechanisms and their frequencies.

The improper use of pediculicides containing permethrin has led to the development of resistance. Thus, new alternatives for control are needed. Plant-derived insecticides are attractive alternatives to common chemical insecticides because most of them are environmentally friendly and non-toxic to mammals. The toxic activity of 23 monoterpenoids belonging to several chemical classes was tested against the eggs of permethrin-resistant head lice, Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae). Significant differences in ovicidal action were observed among the tested substances. The most effective chemicals were hydrocarbons and ethers, followed by ketones, alcohols, phenols and esters. A linear relationship between egg mortality and knockdown time (KT50) on adults by the tested components revealed that most of the components were effective on both egg and adult stages. The monoterpenoids described herein are good candidates as effective pediculicides.

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.

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.

Field populations of Triatoma infestans Klug were collected during 2002 from four villages in northern Argentina (El Chorro, La Toma, El Sauzal, and Salvador Mazza), after application of deltamethrin and other pyrethroids was ineffective. High levels of resistance to the pyrethroid insecticides deltamethrin, beta-cypermethrin, beta-cyfluthrin, and lambda-cyhalothrin were detected in all of the evaluated populations. The resistance ratio to pyrethroids determined by topical application ranged from 50.5 (deltamethrin, El Sauzal) to 667.6 (beta-cyfluthrin, Salvador Mazza). None of the pyrethroid-resistant insects was resistant to the organophosphorus insecticide fenitrothion. Topical application of piperonyl butoxide to the most deltamethrin-resistant population (Salvador Mazza) led to slight reduction in levels of resistance. Activity of P450 monooxygenase, measured in individual insects through ethoxycoumarine-O-deethylase, showed a slight but noticeable difference in the distribution of activities between susceptible and resistant populations. The total percentage of insects below 0.48 pmol of 7-OH coumarine/min/ insect was 36.4 for Salvador Mazza population and 64.3 pmol of 7-OH coumarine/min/insect for CIPEIN strain. Whereas a low level of resistance to deltamethrin was previously related to monooxygenase activity in T. infestans, the high levels of resistance shown by these populations seem to involve monooxygenase in combination with other resistance mechanisms, for example, insensitivity of nervous membrane. Research on T. infestans resistance is in progress to improve Chagas vector control programs in Latin America and to implement resistance management strategies.

Deltamethrin and other pyrethroids have been extensively used in Argentina since 1980, for the chemical control of Triatoma infestans Klug (Hemiptera: Reduviidae). Recently, resistance to deltamethrin was detected in field populations by the survival of bugs exposed by topical application to the diagnostic dose estimated on the CIPEIN susceptible strain. Results of the current study showed low resistant ratios (RRs) to deltamethrin for the resistant populations (RR ranged from 2.0 for San Luis colony to 7.9 for Salta colony). Biochemical studies were made on the most resistant colony (Salta) and the susceptible strain (CIPEIN), in order to establish the importance of degradative mechanisms as a cause of the detected resistance. Esterase activity was measured on 3 days old first instars through phenylthioacetate and a-naphtyl acetate activities. The results showed a significant difference in no cholinesterase esterase activity from susceptible (7.6 +/- 0,7 micro M S./i.min.) and Salta resistant colony (9.5 +/- 0.8 microM S./i.min.). Cytochrome p450 mono-oxygenase (p450) activity was measured on individual insects through ethoxycoumarine deethylase (ECOD) activity using a fluorescence microplate reader. The dependence of ECOD activity on age and body region of the nymphs, and pH and time of incubation were studied in order to optimize the measurement. As a result, comparative studies were performed on abdomens of 2 days old first instars at pH 7.2 and 4 h incubation time. ECOD activity of first nymphs was significantly lower in the susceptible colony (61.3 +/- 9.08 pg ECOD/ insect) than in the resistant one (108.1+/- 5.7 pg ECOD/ insect). These results suggest that degradative esterases (no-cholinesterase) and mono-oxygenases cytochrome p450, play an important role in the resistance to deltamethrin in Salta colony from Argentina.

A series of methyl esters of N-substituted (Z)- and (E)-maleamic acids were synthesized and their effect on food intake measured on fifth-instar nymphs of Triatoma infestans. Suppression of food intake was found only for the (Z)-isomers. The initial reaction rate of the synthesized compounds with glutathione (GSH) was calculated from the reaction in vitro of the (Z)-isomers. No reaction was observed with the (E)-isomers. Good correlation between the suppression of food intake, measured by its ED50 (effective dose that inhibited feeding of 50% of the population) and the initial reaction rate with GSH and the hydrophobic parameter π, was found. © of SCI.

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 μg/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.