Lufenuron is a chitin synthesis inhibitor used for controlling several pest insects. The German cockroach, Blattella germanica, is a cosmopolitan insect of medical and economic importance. Resistance to insecticides has been worldwide reported in this species. The objective of this work was to evaluate the effect of lufenuron in two colonies of B. germanica, one susceptible to insecticides (CIPEIN) and another pyrethroid-resistant (JUBA). Experimental populations from each colony were exposed to flter papers treated with 50 mg of lufenuron/m2. Controls were exposed to flter papers treated with solvent alone. After seven weeks, the average size of both lufenuron-treated populations was 1.33 ± 0.7 individuals, while the average size of control populations were 206.5 ± 39.5 (CIPEIN) and 136.5 ± 43.5 (JUBA) individuals. This drastic effect suggests that lufenuron could be used as an alternative for the control of pyrethroid-resistant German cockroaches. Future studies should explore the toxicity of lufenuron on other populations of B. germanica resistant to pyrethroids or other insecticides.

Lufenurón es un inhibidor de la síntesis de quitina usado para controlar diversas plagas de insectos. La cucaracha alemana, Blattella germanica, es un insecto cosmopolita de importancia médica y económica. Existen numerosos reportes de resistencia a insecticidas en poblaciones de B. germanica alrededor del mundo. El objetivo de este trabajo fue evaluar el efecto de lufenurón en dos colonias de B. germanica, una susceptible a insecticidas (CIPEIN) y otra resistente a deltametrina (JUBA). Se expusieron poblaciones experimentales de ambas colonias a papeles de fltro tratados con 50 mg de lufenurón/m2. Los controles fueron expuestos a papeles de fltro tratados con solvente solo. Al cabo de siete semanas, las dos poblaciones expuestas a lufenurón presentaron el mismo tamaño promedio (1,3 ± 0,7 individuos); mientras que los tamaños promedio de las poblaciones controles fueron 206,5 ± 39,5 (CIPEIN) y 136,5 ± 43,5 individuos (JUBA). Este drástico efecto sobre el tamaño poblacional sugiere que lufenurón podría ser usado como una alternativa para controlar cucarachas alemanas resistentes a deltametrina. A la vista de estos resultados, se debería explorar la toxicidad de lufenurón en otras poblaciones de B. germanica resistentes a piretroides u otros insecticidas.

The bed bug, Cimex lectularius Linnaeus, is a hemimetabolous insect of the family Cimicidae, Order Hemiptera and is a hematophagous ectoparasite of birds and mammals. Two species of this family are predominant: C. lectularius and C. hemipterus Fabricius. Bed bugs have long plagued humans in their living environment. Historically, bed bugs were noted throughout the ages. Before World War II infestations by bed bugs were very common, but after the war the prevalence of infection declined to a point where they were rare, and particularly since the 50s, when cases of infection decreased significantly due to the use of synthetic insecticides, especially dichlorodiphenyltrichloroethane (DDT). However, recently, the situation seems to have changed and experts in the field talk about a "resurgence" of the plague worldwide. Scientific researches and even newspapers' disclosures about bed bugs do nothing more than show that we are in the presence of a major health problem and that our country is no stranger to it. The following study was conducted in order to determine whether bed bugs are resurging in Argentina. The discovery of this urban pest in different cities of Argentina can now be confidently confirmed.

The aim of the present work was to study the deltamethrin susceptibility of eggs from Triatoma infestans populations and the contribution of pyrethroid esterases to deltamethrin degradation. Insects were collected from sylvatic areas, including Veinte de Octubre and Kirus-Mayu (Bolivia) and from domiciliary areas, including El Palmar (Bolivia) and La Pista (Argentina). Deltamethrin susceptibility was determined by dose-response bioassays. Serial dilutions of deltamethrin (0.0005-1 mg/mL) were topically applied to 12-day-old eggs. Samples from El Palmar had the highest lethal dose ratio (LDR) value (44.90) compared to the susceptible reference strain (NFS), whereas the Veinte de Octubre samples had the lowest value (0.50). Pyrethroid esterases were evaluated using 7-coumaryl permethrate (7-CP) on individually homogenised eggs from each population and from NFS. The El Palmar and La Pista samples contained 40.11 and 36.64 pmol/min/mg protein, respectively, and these values were statistically similar to NFS (34.92 pmol/min/mg protein) and different from Kirus-Mayu and Veinte de Octubre (27.49 and 22.69 pmol/min/mg protein, respectively). The toxicological data indicate that the domestic populations were resistant to deltamethrin, but no statistical contribution of 7-CP esterases was observed. The sylvatic populations had similar LDR values to NFS, but lower 7-CP esterase activities. Moreover, this is the first study of the pyrethroid esterases on T. infestans eggs employing a specific substrate (7-CP).

To increase our knowledge of the natural susceptibility of Triatoma infestans to an organophosphate insecticide, we performed toxicological and biochemical studies on three sylvatic populations from Bolivia and two populations from domestic dwellings from Bolivia and Argentina. Fifty-per-cent lethal doses (LD50) were determined based on the topical application of fenitrothion on first instar nymphs and mortality was assessed at 24 h. Both type of populations exhibited LD50ratios significantly higher than 1 with a range of the values (1.42-2.47); the maximum value were found in a sylvatic (-S) population, Veinte de Octubre-S. Samples were biochemically analysed using a glutathione S-transferase activity assay. The highest significant activity was obtained for Veinte de Octubre-S and the lowest activity was obtained for the reference population (102.69 and 54.23 pmol per minute per mg of protein respectively). Two out of the three sylvatic populations (Veinte de Octubre-S and Kirus Mayu-S) exhibited significantly higher glutathione S-transferase activity than that of the reference population. Based on this analysis of the natural susceptibility of this organism to organophosphate insecticides, continental and focal surveys of organophosphate susceptibility should be conducted to evaluate the evolution and distribution of this phenomenon.

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 µM S./i.min.) and Salta resistant colony (9.5 ± 0.8 µM S./i.min.). Cytochrome P450 mono-oxygenase (P450) activity was measured on individual insects through ethoxycoumarine deethylase (ECOD) activity using a fluorescence micro plate 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.