Claudia Vassena

High Resistance to Pyrethroid Insecticides Associated with Ineffective Field Treatments in Triatoma infestans (Hemiptera: Reduviidae) from Northern Argentina

Abstract 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, β-cypermethrin, β-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 (β-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.

Differential patterns of insecticide resistance in eggs and first instars of Triatoma infestans (Hemiptera: Reduviidae) from Argentina and Bolivia.

Abstract Previous work at our laboratory has indicated high resistance levels to deltamethrin correlated with failures of chemical control in field populations of Triatoma infestans (Klug, 1834) (Hemiptera: Reduviidae) in northern Argentina and southern Bolivia. The aim of the present work was to study the resistance patterns in eggs and first instars of T. infestans in populations from Argentina and Bolivia. At the egg stage, a population from Salvador Mazza, Argentina, showed the highest resistance ratio to deltamethrin and lambda-cyhalothrin, and it was susceptible to fipronil and fenitrothion. A population from Mataral, Bolivia, showed very low resistance ratios to deltamethrin and lambda-cyhalothrin, and it was susceptible to fipronil and fenitrothion. A Sucre population was susceptible to deltamethrin and fenitrothion, and it showed very low resistant ratios to lambda-cyhalothrin and fipronil. A Yacuiba population was susceptible to deltamethrin. At the first instar, the Salvador Mazza population was susceptible to fipronil, whereas the Mataral and Sucre populations were susceptible to fenitrothion, and they showed very low resistance ratios to lambda-cyhalothrin but the high resistance to fipronil. The Salvador Mazza population was resistant to deltamethrin at the larval stage. Remarkable differences were found in the resistance profile to fipronil in first instars and eggs from Sucre and Mataral. These indicated that the expression of insecticide resistance in eggs varies between populations and that the pyrethroid resistance diagnosed in T. infestans first instars is not indicative of resistance in the egg stage.

Relative Contribution of Monooxygenase and Esterase to Pyrethroid Resistance in Triatoma infestans (Hemiptera: Reduviidae) from Argentina and Bolivia

Abstract Recently, high resistance to pyrethroid insecticides has been associated with ineffective field treatments against Triatoma infestans (Klug) (Hemiptera: Reduviidae) in northern Argentina. Samples were collected from two areas in Argentina (Salta and La Rioja) and one are in Bolivia (Yacuiba), and they were subjected to toxicological and biochemical assays. All populations were resistant to deltamethrin, but they showed different profiles to nonpyrethroid insecticides. The Salta population showed high resistance ratios (RRs) to deltamethrin and only slight differences in the susceptibility to fenitrothion and fipronil compared with the reference strain. Otherwise, the La Rioja population showed a lower RR to deltamethrin and no resistance to fenitrothion or fipronil. Finally, the Yacuiba population had high a RR to deltamethrin, but it was susceptibility to fenitrothion and fipronil. In several cases, deltamethrin-resistant populations had higher susceptibility to bendiocarb than the reference strain. Measured activity of P450 monooxygenase in individual insects (based on ethoxycoumarine-O-deethylase), tended to be higher in the deltamethrin-resistant populations, but the differences were not statistically significant. Activity of specific esterases determined by the hydrolysis of 7-coumaryl permethrate demonstrated an increase in the percentage of insects with higher esterase activity in the Salta and La Rioja populations. Unexpectedly, the Yacuiba population showed lower pyrethroid esterase activity than the reference strain. The different pyrethroid resistance patterns found in T. infestans from three geographical regions within Argentina and in Bolivia suggests that enzyme-based pyrethroid resistance in this species has multiple origins. Nevertheless, because nerve insensitivity (related to the presence of the kdr gene) is also an important mechanism related to pyrethroid resistance, further studies on the kdr gene should be carried to clarify the relative contribution of each pyrethroid-associated mechanism in deltamethrin-resistant populations of T. infestans.

New findings of insecticide resistance in Triatoma infestans (Heteroptera: Reduviidae) from the Gran Chaco.

ABSTRACT n Chagas disease is a major health concern in Latin America, and Triatoma infestans (Klug, 1834) is responsible for the majority of cases of Chagas disease in the continent. After the discovery of deltamethrin highly resistant populations in the neighboring areas to Yacuiba (Bolivia) and Salvador Mazza (Argentina), we studied T. infestans populations north and southward, with the aim of describing the range of the resistant area. In addition, tests were conducted to describe the susceptibility to fipronil in deltamethrin-resistant populations. Tarija populations were highly resistant to deltamethrin, showing that the resistant area is greater than previously reported. Argentinean and Paraguayan populations were susceptible or presented moderate to low levels of deltamethrin resistance. Resistance to fipronil was found in Bolivian populations, although this insecticide was effective against Argentinean populations. This study shows that the Argentinean and Paraguayan populations are currently under successful control with deltamethrin. However, continuous resistance monitoring is necessary. We found that fipronil is a viable option for Argentina, whereas the resistance found in Bolivia implies that new formulations are needed to control T. infestans in Bolivia. Further research is required to find new alternatives of control in those areas that are currently suffering from high infestation rates.

Prevalence and Levels of Permethrin Resistance in Pediculus humanus capitis De Geer (Anoplura: Pediculidae) from Buenos Aires, Argentina

Abstract 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 μl 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.

Toxic effect of aliphatic alcohols against susceptible and permethrin-resistant Pediculus humanus capitis (Anoplura: Pediculidae)

Abstract 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× for E49 population, RR 9.5× for HL population and RR > 35.3× 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.

Scientific Evidence of Three Different Insecticide-Resistant Profiles in Triatoma infestans (Hemiptera: Reduviidae) Populations from Argentina and Bolivia

ABSTRACT n 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.

Increased Monooxygenase Activity Associated with Resistance to Permethrin in Pediculus humanus capitis (Anoplura: Pediculidae) from Argentina

Abstract 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.

Susceptibility of Sylvatic Triatoma infestans From Andeans Valleys of Bolivia to Deltamethrin and Fipronil

ABSTRACT n We describe the susceptibility to deltamethrin and fipronil of four sylvatic Triatoma infestans populations from the Andean valleys of Bolivia. Fifty percent lethal doses were determined from topical application of insecticide on first instars, and mortality was assessed after 24 h for deltamethrin and 48 h for fipronil. In comparison with a reference strain from Argentina, the Bolivian populations showed deltamethrin 50 percent lethal dose ratios ranging from 1.9 to 17.4. In the case of fipronil, an insecticide never used for control of T. infestans, the Bolivian populations showed even higher variation in toxic response, with relative susceptibilities ranging from 0.5 to 139.2. However, although the sylvatic T. infestans toxicological profiles differ from each other and from those of the domiciliary population studied in this work, there were no significant differences in the activities of P450 mono-oxygenases and pyrethroid esterases between the reference strain and the studied populations.

Comparative efficacy of new commercial pediculicides against adults and eggs of Pediculus humanus capitis (head lice)

The use of pyrethroids to control head louse infestations have suffered considerable loss of efficacy due to the development of resistance. In the last past years, several new alternative products to synthetic pyrethroids have been developed and are sold in the Argentinean market against head lice. The present study investigated the efficacy of two new Argentinean products Nopucid Qubit® and Nopucid Bio Citrus® and its comparison with two reference products Nyda® and Hedrin®. Nopucid Qubit® is a two-phase lotion containing geraniol and citronellol (phase 1) and ciclopentaxiloxane (phase 2); while Nopucid Bio Citrus® contains dimethicone, ciclopentaxiloxane, and bergamot essential oil. These products are physically acting compounds. The sensitivity of two laboratory assays for testing insecticide activity of new formulations was also compared. Mortality (100%) of motile forms occurred after they were exposed to any product for 1 and 2xa0min, either by in vitro or ex vivo test. Concerning ovicidal activity, the most effective pediculicides were Nopucid Bio Citrus® and Nyda®, followed by Hedrin® and Nopucid Qubit®. The present study revealed, for the first time, the efficacy of over-the-counter commercial pediculicides available in Argentine (Nopucid Bio Citrus® and Nopucid Qubit®) on either motile stages or eggs against head lice.