Evaluation of insecticide resistance in Aedes aegypti populations connected by roads and rivers: the case of Tocantins state in Brazil.

BACKGROUND: The longstanding application of insecticides for vector control without periodic monitoring of the population response to these chemicals can directly drive the selection of resistant populations of vector mosquitoes. Tocantins is the newest state of the Brazilian Federation. Despite a historically high number of dengue cases, studies and monitoring data concerning insecticide resistance in the state are lacking. OBJECTIVES: To verify the resistance status of Aedes aegypti from 10 populations distributed throughout the state connected by rivers and roads. METHODS: Between 50 and 150 ovitraps were installed in house gardens within each municipality. Collection points were established based on the importance of the towns and on geographic aspects. Dose response bioassays were performed in accordance with World Health Organization guidelines. Molecular assays were conducted to detect kdr mutations, which are related to pyrethroid resistance. FINDINGS: Of the 3,200 ovitrap paddles analysed, 25.8% contained eggs, with a total of 55,687 eggs collected. With the exception of Caseara, all evaluated populations were considered to be resistant to temephos. The data showed different levels of resistance to deltamethrin among the samples. Caseara and Guaraí showed the lowest RR95 values. On average, the NaVR1 kdr allele was most frequent (40.3%), followed by NaVS (38.1%), and NaVR2 (21.6%). Palmas, the capital of the state, had the highest frequency of kdr alleles (87.5%). MAIN CONCLUSIONS: With the exception of Palmas, the towns with the highest indexes (ovitrap positivity, number and density of eggs), as well with high levels of resistance and kdr alleles were located along the BR-153 road, indicating that the flow of people and cargo can contribute to the dispersion of the vector and potentially resistance. This study contributes substantially to knowledge regarding the insecticide resistance profile of Tocantins mosquito populations; the data generated via the study could facilitate the judicious use of insecticides by vector control programs.

Assessment of the susceptibility status of Aedes aegypti (Diptera: Culicidae) populations to pyriproxyfen and malathion in a nation-wide monitoring of insecticide resistance performed in Brazil from 2017 to 2018.

BACKGROUND: Chemical mosquito control using malathion has been applied in Brazil since 1985. To obtain chemical control effectiveness, vector susceptibility insecticide monitoring is required. This study aimed to describe bioassay standardizations and determine the susceptibility profile of Ae. aegypti populations to malathion and pyriproxyfen, used on a national scale in Brazil between 2017 and 2018, and discuss the observed impacts in arbovirus control. METHODS: The diagnostic-doses (DD) of pyriproxyfen and malathion were determined as the double of adult emergence inhibition (EI) and lethal doses for 99% of the Rockefeller reference strain, respectively. To monitor natural populations, sampling was performed in 132 Brazilian cities, using egg traps. Colonies were raised in the laboratory for one or two generations (F1 or F2) and submitted to susceptibility tests, where larvae were exposed to the pyriproxyfen DD (0.03 µg/l) and adults, to the malathion DD determined in the present study (20 µg), in addition to the one established by the World Health Organization (WHO) DD (50 µg) in a bottle assay. Dose-response (DR) bioassays with pyriproxyfen were performed on populations that did not achieve 98% EI in the DD assays. RESULTS: Susceptibility alterations to pyriproxyfen were recorded in six (4.5%) Ae. aegypti populations from the states of Bahia and Ceará, with Resistance Ratios (RR95) ranging from 1.51 to 3.58. Concerning malathion, 73 (55.3%) populations distributed throughout the country were resistant when exposed to the local DD 20 µg/bottle. On the other hand, no population was resistant, and only 10 (7.6%) populations in eight states were considered as exhibiting decreased susceptibility (mortality ratios between 90 and 98%) when exposed to the WHO DD (50 µg/bottle). CONCLUSIONS: The feasibility of conducting an insecticide resistance monitoring action on a nation-wide scale was confirmed herein, employing standardized and strongly coordinated sampling methods and laboratory bioassays. Brazilian Ae. aegypti populations exhibiting decreased susceptibility to pyriproxyfen were identified. The local DD for malathion was more sensitive than the WHO DD for early decreased susceptibility detection.

Toxicity of spinosad to temephos-resistant Aedes aegypti populations in Brazil.

The mosquito Aedes aegypti is the primary vector of different arboviruses and represents a major public health problem. Several Brazilian populations of Ae. aegypti have developed resistance to temephos, the most used organophosphate larvicide. New tools which are less harmful to the environment and safer for humans are becoming increasingly important to control this insect vector. Spinosad, an aerobic fermentation product of a soil actinobacteria, has a favorable environmental profile. It presents selective insecticide properties, a mechanism of action that differs from those of many synthetic chemical insecticides. The toxicity of spinosad and temephos to Aedes aegypti populations from Brazil, which were previously exposed to temephos, were investigated in this study. Larval susceptibility (LC50) to temephos varied from 3µg/L for Rockefeller up to 260 µg/L for Santana do Ipanema field derived population. Larval susceptibility (LC50) to spinosad varied from 23µg/L for Rockefeller up to 93µg/L for Marilia field derived population. In addition, a semi-field trial was performed to evaluate spinosad (NatularTM DT) initial efficacy and persistence toward four field-derived lineages and the Rockefeller lineage, used as an internal control. Spinosad was tested at 0.5mg active ingredient/L in 200L capacity water tanks. Mortality was recorded each 24 hours after exposition and tanks were further recolonized once per week with mortality being recorded daily for eight weeks. Spinosad provided a level equal or superior to 80% mortality during a seven to eight week evaluation period. The assessed populations did not present cross-resistance between spinosad and temephos in laboratory conditions. It demonstrates that spinosad may be a promising larvicide for the control of Ae. aegypti, especially for populations in which resistance to temephos has been detected.

The mitochondrial genome of the leaf-cutter ant Atta laevigata: a mitogenome with a large number of intergenic spacers.

In this paper we describe the nearly complete mitochondrial genome of the leaf-cutter ant Atta laevigata, assembled using transcriptomic libraries from Sanger and Illumina next generation sequencing (NGS), and PCR products. This mitogenome was found to be very large (18,729 bp), given the presence of 30 non-coding intergenic spacers (IGS) spanning 3,808 bp. A portion of the putative control region remained unsequenced. The gene content and organization correspond to that inferred for the ancestral pancrustacea, except for two tRNA gene rearrangements that have been described previously in other ants. The IGS were highly variable in length and dispersed through the mitogenome. This pattern was also found for the other hymenopterans in particular for the monophyletic Apocrita. These spacers with unknown function may be valuable for characterizing genome evolution and distinguishing closely related species and individuals. NGS provided better coverage than Sanger sequencing, especially for tRNA and ribosomal subunit genes, thus facilitating efforts to fill in sequence gaps. The results obtained showed that data from transcriptomic libraries contain valuable information for assembling mitogenomes. The present data also provide a source of molecular markers that will be very important for improving our understanding of genomic evolutionary processes and phylogenetic relationships among hymenopterans.

Evaluation of insecticide resistance in Aedes aegypti populations connected by roads and rivers: the case of Tocantins state in Brazil

BACKGROUND The longstanding application of insecticides for vector control without periodic monitoring of the population response to these chemicals can directly drive the selection of resistant populations of vector mosquitoes. Tocantins is the newest state of the Brazilian Federation. Despite a historically high number of dengue cases, studies and monitoring data concerning insecticide resistance in the state are lacking. OBJECTIVES To verify the resistance status of Aedes aegypti from 10 populations distributed throughout the state connected by rivers and roads. METHODS Between 50 and 150 ovitraps were installed in house gardens within each municipality. Collection points were established based on the importance of the towns and on geographic aspects. Dose response bioassays were performed in accordance with World Health Organization guidelines. Molecular assays were conducted to detect kdr mutations, which are related to pyrethroid resistance. FINDINGS Of the 3,200 ovitrap paddles analysed, 25.8% contained eggs, with a total of 55,687 eggs collected. With the exception of Caseara, all evaluated populations were considered to be resistant to temephos. The data showed different levels of resistance to deltamethrin among the samples. Caseara and Guaraí showed the lowest RR95 values. On average, the NaVR1 kdr allele was most frequent (40.3%), followed by NaVS (38.1%), and NaVR2 (21.6%). Palmas, the capital of the state, had the highest frequency of kdr alleles (87.5%). MAIN CONCLUSIONS With the exception of Palmas, the towns with the highest indexes (ovitrap positivity, number and density of eggs), as well with high levels of resistance and kdr alleles were located along the BR-153 road, indicating that the flow of people and cargo can contribute to the dispersion of the vector and potentially resistance. This study contributes substantially to knowledge regarding the insecticide resistance profile of Tocantins mosquito populations; the data generated via the study could facilitate the judicious use of insecticides by vector control programs.

Interação entre Trigona spinipes Fabricius, 1793 (Hymenoptera: Apidae ) e Aethalion reticulatum Linnaeus, 1767 (Hemiptera: Aethalionidae) em Mangifera indica (Anacardiaceae) / Interaction between Trigona spinipes Fabricius, 1793 (Hymenoptera: Apidae ) and Aethalion reticulatum Linnaeus, 1767 (Hemiptera: Aethalionidae) in Mangifera indica (Anacardiaceae)

A ocorrência de Aethalion reticulatum, Linnaeus, 1767 (Hemiptera: Aethalionidae) ou cigarrinha do pedúnculo, em manga Mangifera indica (Anacardiaceae), já foi relatada em diversos estados do país. Algumas relações aparentemente comensais podem ocorrer entre cigarrinhas e abelhas sem ferrão, principalmente Trigona spinipes. Nessetrabalho, analisamos a interação entre a abelha Trigona spinipes Fabricius, 1793 (Hymenoptera: Apidae) e a cigarrinha dopedúnculo A. reticulatum, em mangueira. Os comportamentos de T. spinipes defendendo e estimulando a cigarrinha para obter honeydew foram observados e descritos. Essa associação é mutuamente benéfica, sem implicar necessariamente dependência ou interdependência obrigatória. Todavia, a intensa atividade de abelhas solicitando honeydew pode aumentar o consumo de seiva pelas cigarrinhas prejudicando ainda mais o desenvolvimento normal das frutas.

The occurence of Aethalion reticulatum, Linnaeus, 1767 (Hemiptera: Aethalionidae) in mangoMangifera indica (Anacardiaceae), has been reported in many states of this country. Some apparently commensal relations can occur beteween A. reticulatum and stingless bees, specially Trigona. In this work, we analyzed the interaction between Trigona spinipes Fabricius, 1793 (Hymenoptera: Apidae) and A. reticulatum. The defense behaviour as well the stimulation of A. reticulatum by the bee in order to obtain honeydew, were observed and described. This association is mutually beneficial, without implicate in an obligatory dependence or interdependence. However, the intense solicitation of honeydew by the bees can increase the sap consumption what prejudice the fruit production even more.