Mechanisms of acaricide resistance in ticks

Background: In several countries, including Brazil, the livestock industry plays a key role in the country's economy. Brazil has the second largest bovine herd in the world and the biggest commercial herd. Ticks are an ongoing problem for both large operation cattle producers and small family farmers. Rhipicephalus microplus causes expressive losses in cattle breeding, since it occurs in important beef production zones like South America, Africa, and Oceania. Some of the negative consequences of tick infestation to cattle breeding are anemia, loss in milk and beef production, and transmission of Babesia bovis and B. bigemina. Significant losses are caused by the cattle tick (R. microplus) in several regions of the world, costing around US$ 3.3 billion per year to the Brazilian livestock industry alone. The tick control methods are mainly based on synthetic acaricides. However, the improvement of current tick control requires the identification of new molecular targets in tick physiology and development of molecule compounds to target important physiology pathways. The strategies proposed to address this issue are expand the knowledge about the molecules involved in the detoxification of chemicals to enhance the efficacy of the acaricides as well as to develop new compounds for chemical control. Review: Tick control is currently based on chemical acaricides; however, effective control and prevention of tick infestation remain distant goals. In recent decades, a progressive decrease in the efficiency of acaricides due to drug resistance has been observed. Acaricide resistance is an evolutionary adaptation, which implies the existence of behavioral and physiological mechanisms that allow the survival of resistant individuals. Four resistance mechanisms are described: behavioral resistance, reduced drug penetration, target site insensitivity and increased drug detoxification. Augmented drug detoxification may be due to increased activity of enzymes or transporters due to increased gene expression or mutations in some genes. Research focus on mechanisms of acaricide resistance in ticks characterized detoxification pathways based on (1) increased activity of enzymes (cytochrome p450, esterase and GST) which play a role in biochemically altering acaricides towards decreased toxicity and, (2) enhanced excretion of the modified less toxic compounds. To bypass the current problems, a better understanding of the biology, physiology, and molecular biology of the mechanisms of resistance to acaricides is fundamental to prolong their efficiency in controlling ticks. Moreover, identifying the genes and proteins associated with resistance can support in the development of more sensitive diagnostic methods to identify acaricide resistance, as well as improving control strategies. Discussion: In the last years, many researchers have been studying resistance mechanisms and important advances have been made which showed that, in several tick species, ABC transporters, esterases, P-450 cytochromes and glutathione-S-transferases participate in acaricide resistance. The characterization of the alterations in the targets in tick physiology and identification of new drugs with potential to tick control are crucial goals to increase tick control

Preliminary Study on the Differences in Hydrocarbons Between Phosphine-Susceptible and -Resistant Strains of Rhyzopertha dominica (Fabricius) and Tribolium castaneum (Herbst) Using Direct Immersion Solid-Phase Microextraction Coupled with GC-MS.

Phosphine resistance is a worldwide issue threatening the grain industry. The cuticles of insects are covered with a layer of lipids, which protect insect bodies from the harmful effects of pesticides. The main components of the cuticular lipids are hydrocarbon compounds. In this research, phosphine-resistant and -susceptible strains of two main stored-grain insects, T. castaneum and R. dominica, were tested to determine the possible role of their cuticular hydrocarbons in phosphine resistance. Direct immersion solid-phase microextraction followed by gas chromatography-mass spectrometry (GC-MS) was applied to extract and analyze the cuticular hydrocarbons. The results showed significant differences between the resistant and susceptible strains regarding the cuticular hydrocarbons that were investigated. The resistant insects of both species contained higher amounts than the susceptible insects for the majority of the hydrocarbons, sixteen from cuticular extraction and nineteen from the homogenized body extraction for T. castaneum and eighteen from cuticular extraction and twenty-one from the homogenized body extraction for R. dominica. 3-methylnonacosane and 2-methylheptacosane had the highest significant difference between the susceptible and resistant strains of T. castaneum from the cuticle and the homogenized body, respectively. Unknown5 from the cuticle and 3-methylhentriacontane from the homogenized body recorded the highest significant differences in R. dominica. The higher hydrocarbon content is a key factor in eliminating phosphine from entering resistant insect bodies, acting as a barrier between insects and the surrounding phosphine environment.

[Behavioral response and adaptive cost in resistant and susceptible Plutella xylostella to Chlorantraniliprole].

Diamides have been used worldwide to manage the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), however some strains showed resistance to these molecules. Also, pheromone traps could be used to manage this pest, hence reducing the use of insecticides in the field. Resistant DBM strains may have biological disadvantages in comparison to susceptible strains in areas without sprays, including reduction in fitness or behavioral changes. Therefore, the aim of this study was to investigate whether DBM strains resistant to chlorantraniliprole showed adaptive costs that could alter male attraction to the sex pheromone, in comparison to susceptible strains in the laboratory and semi-field conditions. First, the LC1, LC10, LC25, and LC50 of DBM to chlorantraniliprole were established, which were 0.003, 0.005, 0.007, and 0.011 mg a.i. liter-1, and 5.88, 24.80, 57.22, and 144.87 mg a.i. liter-1 for the susceptible and resistant strains, respectively. Development and reproduction of DBM strains subjected to those concentrations were compared. Later, male response to the sex pheromone was investigated in a Y-tube in the laboratory and in a greenhouse to pheromone traps. Resistant DBM strain showed an adaptive cost in comparison to the susceptible strain that can result in a delay in population growth in the field when selection pressure is absent. Conversely, resistant males have no olfactory response alteration in comparison to susceptible males, consistently at 3 (P = 0.6848) and 7 days (P = 0.9140) after release, suggesting that pheromone traps continue to be a viable alternative to manage DBM in an IPM system.

Susceptibility to insecticides and resistance mechanisms in three populations of Aedes aegypti from Peru.

BACKGROUND: Epidemics of dengue, chikungunya and Zika are a growing threat to areas where Aedes aegypti are present. The efficacy of chemical control of Ae. aegypti is threatened by the increasing frequency of insecticide resistance. The objective of this study was to determine the susceptibility status as well as the biochemical and molecular mechanisms underlying insecticide resistance in three populations of Ae. aegypti in high risk areas of dengue, chikungunya, and Zika in Peru. METHODS: Bioassays were conducted on adult Ae. aegypti to evaluate their susceptibility to insecticides used currently or historically for mosquito control in Peru, including six pyrethroids, three organophosphates and one organochlorine, in populations of Ae. aegypti from the districts of Chosica (Department of Lima), Punchana (Department of Loreto) and Piura (Department of Piura). Resistance mechanisms were determined by biochemical assays to assess activity levels of key detoxification enzyme groups (nonspecific esterases, multi-function oxidases, glutathione S-transferases and insensitive acetylcholinesterase). Real-time PCR assays were used to detect two kdr mutations (V1016I and F1534C) on the voltage-gated sodium channel gene. RESULTS: Resistance to DDT was detected in all three populations, and resistance to pyrethroids was detected in all populations except the population from Chosica, which still exhibited susceptibility to deltamethrin. Resistance to organophosphates was also detected, with the exception of populations from Punchana and Piura, which still demonstrated susceptibility to malathion. In general, no increase or alteration of activity of any enzyme group was detected. Both 1016I and 1534C alleles were detected in Punchana and Piura, while only the 1534C allele was detected in Chosica. CONCLUSIONS: The results suggest that resistance to multiple classes of insecticides exist in areas important to Ae. aegypti-borne disease transmission in Peru. The F1534C mutation was present in all 3 populations and the V1016I mutation was present in 2 populations. To our knowledge, this is the first report of the presence of 1016I and 1534C in Ae. aegypti in Peru. The absence of highly elevated enzymatic activity suggests that target site resistance is a key mechanism underlying insecticide resistance in these populations, although further research is needed to fully understand the role of metabolic resistance mechanisms in these populations.

Multiple insecticide resistance in Culex quinquefasciatus populations from Guadeloupe (French West Indies) and associated mechanisms.

West Nile (WN) virus has been detected in Guadeloupe since 2002. Even if no WN human cases have been detected so far, mosquitoes from Culex genus especially Culex quinquefasciatus are recognized as potential WN vectors in Guadeloupe. To evaluate the impact of local vector control activities on this mosquito species we assessed the resistance levels of Cx. quinquefasciatus populations from three different sites from Guadeloupe (Abymes, Saint François and Gourbeyre) to malathion, temephos and deltamethrin. In addition, the frequencies of the L1014F kdr and the G119S ace-1 mutations were established in Cx. quinquefasciatus populations, as well as the constitutive expressions of five cytochrome P450 genes. Mosquito populations tested displayed high resistance to deltamethrin, moderate resistance to malathion (Abymes, Gourbeyre) and low resistance to temephos (Abymes et Gourbeyre). Molecular analyses revealed high frequencies of both L1014F kdr and G119S ace-1 mutations in Cx. quinquefasciatus populations, as well as overexpression of cytochrome P450 genes CYP9J45, CYP9J40 and CYP6AA7. Finally, deltamethrin resistance and knock-down rates were strongly correlated with the frequency of the resistant kdr and ace-1 alleles, as well as with CYP9J40 overexpression. These results should be taken into account to refine the current vector control strategies to prevent the appearance of Cx. quinquefasciatus-borne diseases in Guadeloupe.

Effective dominance of resistance of Spodoptera frugiperda to Bt maize and cotton varieties: implications for resistance management.

The resistance of fall armyworm (FAW), Spodoptera frugiperda, has been characterized to some Cry and Vip3A proteins of Bacillus thuringiensis (Bt) expressed in transgenic maize in Brazil. Here we evaluated the effective dominance of resistance based on the survival of neonates from selected Bt-resistant, heterozygous, and susceptible (Sus) strains of FAW on different Bt maize and cotton varieties. High survival of strains resistant to the Cry1F (HX-R), Cry1A.105/Cry2Ab (VT-R) and Cry1A.105/Cry2Ab/Cry1F (PW-R) proteins was detected on Herculex, YieldGard VT PRO and PowerCore maize. Our Vip3A-resistant strain (Vip-R) exhibited high survival on Herculex, Agrisure Viptera and Agrisure Viptera 3 maize. However, the heterozygous from HX-R × Sus, VT-R × Sus, PW-R × Sus and Vip-R × Sus had complete mortality on YieldGard VT PRO, PowerCore, Agrisure Viptera, and Agrisure Viptera 3, whereas the HX-R × Sus and Vip-R × Sus strains survived on Herculex maize. On Bt cotton, the HX-R, VT-R and PW-R strains exhibited high survival on Bollgard II. All resistant strains survived on WideStrike, but only PW-R and Vip-R × Sus survived on TwinLink. Our study provides useful data to aid in the understanding of the effectiveness of the refuge strategy for Insect Resistance Management of Bt plants.

High Susceptibility to Cry1Ac and Low Resistance Allele Frequency Reduce the Risk of Resistance of Helicoverpa armigers to Bt Soybean in Brazil.

The Old World bollworm, Helicoverpa armigera (Hübner), was recently introduced into Brazil, where it has caused extensive damage to cotton and soybean crops. MON 87701 × MON 89788 soybean, which expresses the Bt protein Cry1Ac, was recently deployed in Brazil, providing high levels of control against H. armigera. To assess the risk of resistance to the Cry1Ac protein expressed by MON 87701 × MON 89788 soybean in Brazil, we conducted studies to evaluate the baseline susceptibility of H. armigera to Cry1Ac, in planta efficacy including the assessment of the high-dose criterion, and the initial resistance allele frequency based on an F2 screen. The mean Cry1Ac lethal concentration (LC50) ranged from 0.11 to 1.82 µg·mL-1 of diet among all H. armigera field populations collected from crop seasons 2013/14 to 2014/15, which indicated about 16.5-fold variation. MON 87701 × MON 89788 soybean exhibited a high level of efficacy against H. armigera and most likely met the high dose criterion against this target species in leaf tissue dilution bioassays up to 50 times. A total of 212 F2 family lines of H. armigera were established from field collections sampled from seven locations across Brazil and were screened for the presence of MON 87701 × MON 89788 soybean resistance alleles. None of the 212 families survived on MON 87701 × MON 89788 soybean leaf tissue (estimated allele frequency = 0.0011). The responses of H. armigera to Cry1Ac protein, high susceptibility to MON 87701 × MON 89788 soybean, and low frequency of resistance alleles across the main soybean-producing regions support the assumptions of a high-dose/refuge strategy. However, maintenance of reasonable compliance with the refuge recommendation will be essential to delay the evolution of resistance in H. armigera to MON 87701 × MON 89788 soybean in Brazil.

Ontogenic behavioral consistency, individual variation and fitness consequences among lady beetles.

The potential relevance of complete metamorphosis for the individual variation in sets of behavioral traits and their fitness consequences in predatory species led to the present study. A set of nine behavioral traits were assessed for the larvae and adults of a pyrethroid-resistant and a susceptible population of the lady beetle Eriopis connexa. The aim was to assess: 1) the average individual behavioral (pheno)types and their within-population variation, 2) their ontogenic behavioral consistency from larva to adult, and 3) whether the observed correlated sets of behavioral traits can impact fitness. The average behavioral type differed between populations. The pyrethroid-resistant population consistently exhibited lower aggressiveness (as larvae) and exploration, but showed higher activity, as well as larva sociality, and sometimes boldness than the susceptible population. Behavioral trait variation was higher among pyrethroid-resistant individuals, particularly during the larval stage, but there was significant behavior correlation between larvae and adults, regardless of the insect population. Reduced aggressiveness, and to a lesser extent intermediate levels of boldness against heterospecific individuals were associated with higher population growth. Besides shedding light on the ontogenic consistency of behavioral traits and their fitness impact, our results also suggest that reduced aggressiveness is associated with predator population increase, but may compromise its effectiveness as a biocontrol agent.

Estado de la resistencia a insecticidas en Aedes aegypti (Diptera: Culicidae) del municipio Pinar del Río / Situation of resistance to insecticides in Aedes aegypti (Diptera: Culicidae) from Pinar del Rio municipality

Introducción: el programa de control de Aedes aegypti (Linnaeus) (Diptera: Culicidae) en Cuba utiliza temefos como larvicida y piretroides como adulticidas, aunque el organofosforado clorpirifos ha sido utilizado esporádicamente. Conocer el nivel de resistencia a estos insecticidas es esencial para lograr un control efectivo de esta especie. Objetivo: determinar el nivel de resistencia a insecticidas en su grado técnico y en sus formulaciones comerciales en Ae. aegypti de Pinar del Río. Métodos: una cepa de Ae. aegypti del Área de Salud Raúl Sánchez, Pinar del Río, fue evaluada a través de los bioensayos de la Organización Mundial de la Salud para determinar la susceptibilidad en larvas al organofosforado temefos en su formulación técnica. Se evaluaron además tres formulaciones granuladas de temefos (Abatex-G1, Biolarv G-1 y Temefar G-1). En el estado adulto se determinó el nivel de susceptibilidad a los insecticidas piretroides: cipermetrina, deltametrina, lambdacialotrina y al organofosforado clorpirifos, en su formulación técnica. Además se evaluaron algunos en su formulación comercial: Galgotrin 25 EC (cipermetrina), Aqua K-Otrina 2 EW (deltametrina) y Clorcide 44 EC (clorpirifos). Resultados: en larvas, se encontró alta resistencia a temefos, en su formulación técnica, y con los productos en su formulación comercial, se observó una efectividad del 100 por ciento, con recambio diario de agua, de hasta 20 días para Temefar G1, 18 días para Biolarv G1 y 12 días para Abatex G1. En los ensayos de adultos, la cepa resultó susceptible a cipermetrina, deltametrina y clorpirifos, y resistente a lambdacialotrina. Con respecto a las tres formulaciones comerciales evaluadas, solo se observó resistencia a Aqua K-Otrina 2 EW. Conclusiones: el uso de estrategias de control integrado de Ae. aegypti se hace necesario para disminuir la frecuencia de uso de temefos, y así recuperar la efectividad de este insecticida. Además, se evitaría la aparición de resistencia a productos adulticidas que aun mantienen su efectividad para el control efectivo de esta especie en la zona de estudio(AU)

Introduction: the control program of Aedes aegypti (Linnaeus) (Diptera: Culicidae) in Cuba uses temephos as larvicide and pyrethroids as adulticide although the organophosphorate chlorpyrifos has been barely used. The level of knowledge about resistance to insecticides is essential to effectively control this species. Objective: to determine the level of resistance to insecticides of Ae. aegypti from Pinar del Rio in its technical aspect and in commercial formulations. Methods: one Ae. aegypti strain from the health area Raul Sánchez in Pinar del Rio province was evaluated through the World Health Organization bioassays to determine susceptibility of larvae to temephos in its technical formulation. Additionally, three granulated formulations of temephos were evaluated (Abatex-G1, Biolarv G-1 and Temefar G-1). In the adult state, the level of susceptibility to pyrethroids called cypermethrin, deltamethrin, lambda cyhalothrine and to organophosphate chlorpyrifos in its technical formulation. Some of them were evaluated in its commercial formulation (Galgotrin 25 EC (cypermethrin), Aqua K-Otrina 2 EW (deltamethrin) and Clorcide 44 EC (chlorpyrifos). Results: it was found in larvae that the resistance to temephos was high in the technical formulation, but the commercial formulation showed an effectiveness rate of 100 percent., with daily change of water, up to 20 days for Temefar G1, 18 days for Biolarv G1 and 12 for Abatex G1. In the assays with adult vectors, the strain turned to be susceptible to cypermethrin, deltamethrin and chlorpyrifos and resistant to lambda cyhalothrin. Regarding the three evaluated commercial formulations, resistance to Aqua K-Otrina 2 EW was proved. Conclusions: the use of integrated control strategies for Ae. aegypti makes it necessary to reduce the frequency of use of temephos and to recover the effectiveness of this insecticide. Moreover, it will avoid the occurrence of resistance to adulticide products that are still effective for the control of this species in the study area(AU)

Resistance Status to the Insecticides Temephos, Deltamethrin, and Diflubenzuron in Brazilian Aedes aegypti Populations.

Insecticides are still largely applied in public health to control disease vectors. In Brazil, organophosphates (OP) and pyrethroids (PY) are used against Aedes aegypti for years. Since 2009 Insect Growth Regulators (IGR) are also employed in the control of larvae. We quantified resistance to temephos (OP), deltamethrin (PY), and diflubenzuron (IGR) of A. aegypti samples from 12 municipalities distributed throughout the country, collected between 2010 and 2012. High levels of resistance to neurotoxic insecticides were detected in almost all populations: RR95 to temephos varied between 4.0 and 27.1; the lowest RR95 to deltamethrin was 13.1, and values higher than 70.0 were found. In contrast, all samples were susceptible to diflubenzuron (RR95 < 2.3). Biochemical tests performed with larvae and adults discarded the participation of acetylcholinesterase, the OP target, and confirmed involvement of the detoxifying enzymes esterases, mixed function oxidases, and glutathione-S-transferases. The results obtained were discussed taking into account the public chemical control component and the increase in the domestic use of insecticides during dengue epidemic seasons in the evaluated municipalities.

Deltamethrin-mediated survival, behavior, and oenocyte morphology of insecticide-susceptible and resistant yellow fever mosquitos (Aedes aegypti).

Insecticide use is the prevailing control tactic for the mosquito Aedes aegypti, a vector of several human viruses, which leads to ever-increasing problems of insecticide resistance in populations of this insect pest species. The underlying mechanisms of insecticide resistance may be linked to the metabolism of insecticides by various cells, including oenocytes. Oenocytes are ectodermal cells responsible for lipid metabolism and detoxification. The goal of this study was to evaluate the sublethal effects of deltamethrin on survival, behavior, and oenocyte structure in the immature mosquitoes of insecticide-susceptible and resistant strains of A. aegypti. Fourth instar larvae (L4) of both strains were exposed to different concentrations of deltamethrin (i.e., 0.001, 0.003, 0.005, and 0.007 ppm). After exposure, L4 were subjected to behavioral bioassays. Insecticide effects on cell integrity after deltamethrin exposure (at 0.003 or 0.005 ppm) were assessed by processing pupal oenocytes for transmission electron microscopy or TUNEL reaction. The insecticide resistant L4 survived all the tested concentrations, whereas the 0.007-ppm deltamethrin concentration had lethal effects on susceptible L4. Susceptible L4 were lethargic and exhibited less swimming activity than unexposed larvae, whereas the resistant L4 were hyperexcited following exposure to 0.005 ppm deltamethrin. No sublethal effects and no significant cell death were observed in the oenocytes of either susceptible or resistant insects exposed to deltamethrin. The present study illustrated the different responses of susceptible and resistant strains of A. aegypti following exposure to sublethal concentration of deltamethrin, and demonstrated how the behavior of the immature stage of the two strains varied, as well as oenocyte structure following insecticide exposure.

Organophosphate Resistance and its Main Mechanism in Populations of Codling Moth (Lepidoptera: Tortricidae) from Central Chile.

The codling moth, Cydia pomonella (L.), is the key pest of apple production worldwide. Insecticide resistance has been reported in all producing countries, based on five different mechanisms. Codling moth in Chile has resistance to azinphos-methyl and tebufenozide in post-diapausing larvae. However, there are no studies about the susceptibility of these populations to insecticides from other chemical groups. Therefore, the efficacy of azinphos-methyl, chlorpyrifos-ethyl, esfenvalerate, methoxyfenozide, tebufenozide, and thiacloprid on neonate and post-diapausing larvae from six field populations was investigated, and identified resistance mechanisms in this species were evaluated. Neonate larvae were susceptible to all insecticides studied, but post-diapausing larvae from four populations were resistant to chlorpyrifos, one of them was also resistant to azinphos-methyl, and another one was resistant to tebufenozide. The acetylcholinesterase insensitivity mutation was not detected, and the sodium channel knockdown resistance mutation was present in a low frequency in one population. Detoxifying enzymatic activity of glutathione S-transferases, esterases, and cytochrome P-450 monooxygenases in adults differed among populations, but chlorpyrifos resistance was associated only with a decreased esterase activity as shown by a significant negative correlation between chlorpyrifos mortality and esterase activity.

Metabolic and Behavioral Mechanisms of Indoxacarb Resistance in Sitophilus zeamais (Coleoptera: Curculionidae).

The control of the most important pest of stored maize, the weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), is mainly achieved with the use of pyrethroid insecticides. However, the intensive use of these compounds has led to the selection of resistant populations and has compromised the control efficacy of this insect pest. Here, the toxicity of indoxacarb for a potential use in the control of S. zeamais was assessed on 13 Brazilian populations. Concentration-mortality bioassays, in the presence of synergists (piperonyl butoxide, triphenyl phosphate, and diethyl maleate), were used to assess potential metabolic-based indoxacarb resistance mechanisms. We also assessed the behavioral (locomotory) responses of these populations to indoxacarb exposure. The results showed significant differences between the populations (LD50 values ranged from 0.06 to 13.99 mg a.i/kg of grains), resulting in resistance ratios of >200-fold between the least (Canarana-MT) and the most (Espirito Santo do Pinhal-SP) susceptible populations. The results obtained with synergized indoxacarb suggest the involvement of esterases and glutathione-S-transferases on indoxacarb action, and also suggest the involvement of cytochrome P450-dependent monooxygenases as a potential indoxacarb resistance mechanism in Brazilian populations of S. zeamais. Although indoxacarb-induced behavioral avoidance varied among populations, some resistant populations (e.g., Canarana-MT) were able to reduce exposure to indoxacarb by spending more time in the nontreated areas. Collectively, our findings indicate that the behavioral (locomotory) and physiological responses of these insects may compromise the control efficacy of oxadiazine insecticides (e.g., indoxacarb) in Brazilian populations of S. zeamais.

Cross-Resistance between Cry1 Proteins in Fall Armyworm (Spodoptera frugiperda) May Affect the Durability of Current Pyramided Bt Maize Hybrids in Brazil.

Genetically modified plants expressing insecticidal proteins from Bacillus thuringiensis (Bt) offer valuable options for managing insect pests with considerable environmental and economic benefits. Despite the benefits provided by Bt crops, the continuous expression of these insecticidal proteins imposes strong selection for resistance in target pest populations. Bt maize (Zea mays) hybrids have been successful in controlling fall armyworm (Spodoptera frugiperda), the main maize pest in Brazil since 2008; however, field-evolved resistance to the protein Cry1F has recently been reported. Therefore it is important to assess the possibility of cross-resistance between Cry1F and other Cry proteins expressed in Bt maize hybrids. In this study, an F2 screen followed by subsequent selection on MON 89034 maize was used to select an S. frugiperda strain (RR) able to survive on the Bt maize event MON 89034, which expresses the Cry1A.105 and Cry2Ab2 proteins. Field-collected insects from maize expressing the Cry1F protein (event TC1507) represented most of the positive (resistance allele-containing) (iso)families found. The RR strain showed high levels of resistance to Cry1F, which apparently also conferred high levels of cross resistance to Cry1A.105 and Cry1Ab, but had only low-level (10-fold) resistance to Cry2Ab2. Life history studies to investigate fitness costs associated with the resistance in RR strain revealed only small reductions in reproductive rate when compared to susceptible and heterozygous strains, but the RR strain produced 32.2% and 28.4% fewer females from each female relative to the SS and RS (pooled) strains, respectively. Consistent with the lack of significant resistance to Cry2Ab2, MON 89034 maize in combination with appropriate management practices continues to provide effective control of S. frugiperda in Brazil. Nevertheless, the occurrence of Cry1F resistance in S. frugiperda across Brazil, and the cross-resistance to Cry1Ab and Cry1A.105, indicates that current Cry1-based maize hybrids face a challenge in managing S. frugiperda in Brazil and highlights the importance of effective insect resistance management for these technologies.

Spinosad and the tomato borer Tuta absoluta: a bioinsecticide, an invasive pest threat, and high insecticide resistance.

The introduction of an agricultural pest species into a new environment is a potential threat to agroecosystems of the invaded area. The phytosanitary concern is even greater if the introduced pest's phenotype expresses traits that will impair the management of that species. The invasive tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is one such species and the characterization of the insecticide resistance prevailing in the area of origin is important to guide management efforts in new areas of introduction. The spinosad is one the main insecticides currently used in Brazil for control of the tomato borer; Brazil is the likely source of the introduction of the tomato borer into Europe. For this reason, spinosad resistance in Brazilian populations of this species was characterized. Spinosad resistance has been reported in Brazilian field populations of this pest species, and one resistant population that was used in this study was subjected to an additional seven generations of selection for spinosad resistance reaching levels over 180,000-fold. Inheritance studies indicated that spinosad resistance is monogenic, incompletely recessive and autosomal with high heritability (h(2) = 0.71). Spinosad resistance was unstable without selection pressure with a negative rate of change in the resistance level ( = -0.51) indicating an associated adaptive cost. Esterases and cytochrome P450-dependent monooxygenases titration decreased with spinosad selection, indicating that these detoxification enzymes are not the underlying resistance mechanism. Furthermore, the cross-resistance spectrum was restricted to the insecticide spinetoram, another spinosyn, suggesting that altered target site may be the mechanism involved. Therefore, the suspension of spinosyn use against the tomato borer would be a useful component in spinosad resistance management for this species. Spinosad use against this species in introduced areas should be carefully monitored to prevent rapid selection of high levels of resistance and the potential for its spread to new areas.

Geometric morphometrics of nine field isolates of Aedes aegypti with different resistance levels to lambda-cyhalothrin and relative fitness of one artificially selected for resistance.

Aedes aegypti, a mosquito closely associated with humans, is the principal vector of dengue virus which currently infects about 400 million people worldwide. Because there is no way to prevent infection, public health policies focus on vector control; but insecticide-resistance threatens them. However, most insecticide-resistant mosquito populations exhibit fitness costs in absence of insecticides, although these costs vary. Research on components of fitness that vary with insecticide-resistance can help to develop policies for effective integrated management and control. We investigated the relationships in wing size, wing shape, and natural resistance levels to lambda-cyhalothrin of nine field isolates. Also we chose one of these isolates to select in lab for resistance to the insecticide. The main life-traits parameters were assessed to investigate the possible fitness cost and its association with wing size and shape. We found that wing shape, more than wing size, was strongly correlated with resistance levels to lambda-cyhalothrin in field isolates, but founder effects of culture in the laboratory seem to change wing shape (and also wing size) more easily than artificial selection for resistance to that insecticide. Moreover, significant fitness costs were observed in response to insecticide-resistance as proved by the diminished fecundity and survival of females in the selected line and the reversion to susceptibility in 20 generations of the non-selected line. As a practical consequence, we think, mosquito control programs could benefit from this knowledge in implementing efficient strategies to prevent the evolution of resistance. In particular, the knowledge of reversion to susceptibility is important because it can help in planning better strategies of insecticide use to keep useful the few insecticide-molecules currently available.

Toxicological and biochemical analysis of the susceptibility of sylvatic Triatoma infestans from the Andean Valley of Bolivia to organophosphate insecticide.

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.

Toxicological and biochemical analysis of the susceptibility of sylvatic Triatoma infestans from the Andean Valley of Bolivia to organophosphate insecticide

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.

Survival and behavioural responses of the predatory ladybird beetle, Eriopis connexa populations susceptible and resistant to a pyrethroid insecticide.

The ladybird beetle, Eriopis connexa (Germar) (Coleoptera: Coccinellidae), is one of the commonest predators of aphids (Hemiptera: Aphididae) in the cotton agroecosystem and in many other row and fruit crops in Brazil, and has been introduced into other countries such as the USA for purposes of aphid control. In addition, the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae) is the most serious cotton pest where it occurs, including Brazil. Controlling boll weevils and other pests such as cotton defoliators still tends to involve the intense application of insecticides to secure cotton production. The pyrethroid insecticide lambda-cyhalothrin (LCT) is commonly used, but this compound is not effective against aphids; hence, a desirable strategy would be to maintain E. connexa populations in cotton fields where LCT is applied. Using populations of E. connexa resistant (Res) and susceptible (Sus) to LCT, we compared behavioural responses on treated cotton plants and under confinement on partially and fully treated surfaces, and assessed the insects' survival on treated plants compared with that of the boll weevil. The E. connexa resistant population caged on treated plants with 15 and 75 g a.i. ha-1 exhibited ≫82% survival for both insecticide concentrations compared with ≪3% and ≪17% survival for susceptible E. connexa populations and boll weevils, respectively. The response of E. connexa Res and Sus populations when released, either on the soil or on the plant canopy, indicated avoidance towards treated plants, as measured by elapsed time to assess the plant. When compared with susceptible individuals, resistant ones took longer time to suffer insecticide knockdown, had a higher recovery rate after suffering knockdown, and spent more time in the plant canopy. Based on behavioural parameters evaluated in treated arenas, no ladybird beetles exhibited repellency. However, irritability was evident, with the susceptible population exhibiting greater irritability compared with the resistant population and a subgroup comprising resistant individuals that had recovered from knockdown. The outcomes for the E. connexa Res population indicate a promising strategy for its maintenance when using the insecticide LCT in integrated pest management schemes to control boll weevil or other non-target pest of ladybird beetles in cotton fields.

Pyrethroid resistance in Aedes aegypti and Aedes albopictus from Port-au-Prince, Haiti.

In Port-au-Prince, Haiti, the status of insecticide resistance has not recently been evaluated for Aedes aegypti (L) and Aedes albopictus (Skuse) populations. No prophylactics exist for dengue, so prevention is only through vector control methods. An earthquake occurred in Haiti on January 12, 2010, with a magnitude of 7.0 Mw that devastated the area. Dengue became a major concern for the humanitarian relief workers that entered the country. Bottle bioassays were conducted in the field on adult mosquitoes reared from larvae collected from the grounds of the U.S. Embassy and from an adjacent neighborhood in eastern Port-au-Prince, Haiti. At the CDC, Fort Collins, CO, bioassays, molecular, and biochemical assays were performed on mosquitoes reared from field-collected eggs. A small percentage of the population was able to survive the diagnostic dose in bioassays run in Haiti. Mosquitoes tested at the CDC demonstrated no phenotypic resistance. A variety of factors could be responsible for the discrepancies between the field and lab data, but temperature and larval nutrition are probably most important. Knowledge of localized resistance and underlying mechanisms helps in making rational decisions in selection of appropriate and effective insecticides in the event of a dengue outbreak.