Resumo O óleo essencial de citronela (Cymbopogon winterianus) possui diversas atividades biológicas, entre elas a ação repelente a insetos. Alguns estudos mostraram que os ésteres do ácido cinâmico podem ser aplicados como pesticidas naturais, inseticidas e fungicidas. Nesse contexto, o objetivo do presente trabalho foi avaliar a produção de ésteres a partir do óleo essencial de citronela com ácido cinâmico via esterificação enzimática. Além disso, foi investigada a toxicidade do óleo essencial antes e após a esterificação contra Artemia salina e a ação larvicida sobre Aedes aegypti. Os ésteres foram produzidos utilizando ácido cinâmico como agente acilante e óleo essencial de citronela (3: 1) em heptano e 15% em peso da enzima NS 88011 como biocatalisadores, a 70 ° C e 150 rpm. As taxas de conversão de cinamatos de citronelil e geranil foram 58,7 e 69,0% para NS 88011, respectivamente. Para a toxicidade sobre Artemia salina foram obtidos CL50 de 5,29 μg mL-1 para o óleo essencial e 4,36 μg mL-1 para os óleos esterificados com NS 88011. Na atividade inseticida contra larvas de Aedes aegypti, obteve-se CL50 de 111,84 μg mL-1 para o óleo essencial de citronela e 86,30 μg mL-1 para os óleos esterificados com a enzima NS 88011, indicando alta toxicidade dos ésteres. Os resultados demonstraram que as amostras avaliadas apresentam potencial de aplicação como bioinseticida.

Abstract The essential oil of citronella (Cymbopogon winterianus) has several biological activities, among them the insect repellent action. Some studies showed that cinnamic acid esters can be applied as natural pesticides, insecticides and fungicides. In this context, the objective of the present work was to evaluate the production of esters from citronella essential oil with cinnamic acid via enzymatic esterification. Besides, the essential oil toxicity before and after esterification against Artemia salina and larvicidal action on Aedes aegypti was investigated. Esters were produced using cinnamic acid as the acylating agent and citronella essential oil (3:1) in heptane and 15 wt% NS 88011 enzyme as biocatalysts, at 70 °C and 150 rpm. Conversion rates of citronellyl and geranyl cinnamates were 58.7 and 69.0% for NS 88011, respectively. For the toxicity to Artemia salina LC50 results of 5.29 μg mL-1 were obtained for the essential oil and 4.36 μg mL-1 for the esterified oils obtained with NS 88011. In the insecticidal activity against Aedes aegypti larvae, was obtained LC50 of 111.84 μg mL-1 for the essential oil of citronella and 86.30 μg mL-1 for the esterified oils obtained with the enzyme NS 88011, indicating high toxicity of the esters. The results demonstrated that the evaluated samples present potential of application as bioinsecticide.

ABSTRACT Because of the current scenario of the SARS-CoV-2 (COVID-19) pandemic in Brazil, whose vaccination campaign is in its initial stage, government authorities have pointed towards the complete reopening of the economy. And recently, for the in-personal return of classroom teaching in schools. Given the family relationship, one of the questions that remains without an answer is: what are the consequences of the schools’ reopening on the dissemination of COVID-19? The purpose of this work is to analyze a variant of the compartmental SIRD (Susceptible, Infected, Recovered, Social Distancing) model in a structured, interacting age population representing six age groups, from the basic education age to the elderly. We present a complete analysis of the well-posedness of the proposed mathematical model. We discuss distinct disease spreading scenarios based on observations of the mathematical behavior of the proposed dynamics. Moreover, we present the existence of the stationary points in terms of the parameters of the model and the number of infected age groups. Finally, we present different numerical simulations of the predicted scenarios by the model. Those numerical realizations support the conclusion that an early school reopening, resulting in the decreasing social isolation of young people, causes the infection curve to grow considerably, even for other age groups.

The knowledge of mosquitoes Culicidae host feeding patterns is basic to understand the roles of different species and to indicate their importance in the epidemiology of arthropod-borne diseases. A laboratory assay was developed aiming at standardizing the biotin-avidin sandwich enzyme-linked immunosorbent assay, which was unprecedented for mosquito blood meal identification. The enzyme-linked immunosorbent assay (ELISA) activity was evaluated by the detection of titers on each sample of the 28 blood-fed Culex quinquefasciatus. In light of the high sensitivity that the technique permits, by means of small quantities of specific antibodies commercially provided and phosphatase substrate which reinforces additional dilutions, human and rat blood meals were readily identified in all laboratory-raised Culex quinquefasciatus tested. The assay was effective to detect human blood meal dilutions up to 1:4,096, which enables the technique to be applied in field studies. Additionally, the present results indicate a significant difference between the detection patterns recorded from human blood meal which corroborate the results of host feeding patterns.

As distribuições do carbono da biomassa microbiana (CBM), da atividade enzimática e do C mineralizável foram avaliadas em agregados, coletados na profundidade de 0-0,05 m, de um Latossolo Vermelho-Escuro argiloso, sob vegetação nativa de Cerrado e sob sistemas de plantio direto (PD) e convencional com arado de discos (PC), estabelecidos há 21 anos. A separação dos agregados foi realizada por via úmida. As classes de 8,00-2,00 mm; 0,50-0,25 mm e 0,25-0,106 mm e amostras denominadas soma de agregados foram selecionadas para as determinações biológicas. Em relação à área nativa, os sistemas cultivados causaram quebra de macroagregados e perda de CBM. A aplicação localizada de adubos, o menor revolvimento do solo e os maiores teores de matéria orgânica no PD favoreceram, em relação ao PC, a ocorrência de maiores níveis de fosfatase ácida e arilsulfatase nos agregados e nas amostras que representavam a soma de agregados. Os microagregados e a soma dos agregados do PD também apresentaram maiores teores de CBM, comparativamente ao PC. As maiores atividades da beta-glucosidase foram observadas nos macro e microagregados do PD. Os sistemas de manejo (PD e PC) influenciaram a distribuição das propriedades biológicas nos agregados. A atividade das enzimas beta-glucosidase, fosfatase ácida e arilsulfatase foi maior em macroagregados do PD apesar da distribuição semelhante do CBM nas três classes de agregados avaliadas. No PC, apenas beta-glucosidase apresentou distribuição diferenciada entre macro e microagregados.

The distributions of microbial biomass carbon (MBC), enzymes activities and readily mineralizable carbon were evaluated across soil aggregates recovered from a Dark-Red Clayey Oxisol in areas under native Cerrado vegetation and where no-tillage (NT) and conventional tillage (CT) management systems have been established for 21 years. Soil samples were collected at a 0 to 5 cm depth and aggregates were prepared using a wet sieving procedure. The size classes 8.0 to 2.0 mm, 0.5 to 0.25 mm and 0.25 to 0.106 mm and samples denominated sum of aggregates (SA) were selected for biological determinations. In relation to the native Cerrado the agricultural systems caused the disruption of macroaggregates and losses of MBC. As compared to the CT, the reduced soil tillage, the accumulation of organic matter and the localized application of fertilizers in the NT system favored higher levels of acid phosphatase and arylsulfatase in its aggregates and SA samples. NT microaggregates and SA samples presented higher levels of MBC as compared do the CT. The highest activities of beta-glucosidase were also found in the NT macro and microaggregates. The NT and CT management systems influenced the distribution profile, in soil aggregates, of the biological properties evaluated. Acid phosphatase, beta-glucosidase and arylsulfatase activities were higher in the NT macroaggregates, in spite of the evenly distribution of MBC in the three aggregate size classes evaluated. In the CT, only beta-glucosidase presented an uneven distribution in macro and microaggregates.

Estudaram-se a distribuição, a acumulação de carbono orgânico (C) e o papel do solo como fonte ou depósito de C-CO2 em perfis de Latossolo Vermelho-Escuro (LE) argiloso e muito argiloso. As avaliações foram realizadas nos campos experimentais da Embrapa Cerrados, Planaltina, Distrito Federal, em seis sistemas de manejo: vegetação típica de cerrado (CE), reflorestamento de eucalipto (EU), pastagem cultivada (PA), preparo com grade pesada (GP), preparo com arado de discos (AD), plantio direto (PD), estabelecidos por mais de doze anos, na região dos Cerrados. O C foi analisado em amostras de solo coletadas no perfil até à profundidade de 100 cm. O balanço de C dos outros sistemas em relação ao CE foi utilizado para analisar o comportamento do solo como fonte ou depósito de C-CO2. As alterações mais importantes na dinâmica do C, no que se refere a adições, perdas e distribuição, ocorreram nas camadas superficiais. Em relação ao sistema natural (CE), verificou-se que a acumulação de C foi maior nos sistemas com menor intensidade de perturbação do solo (PD, PA e EU) e menor nos sistemas mais perturbados (AD e GP). Os solos sob PD, PA e EU funcionaram como depósito e os solos sob GP e AD como fonte de CO2.

Carbon storage and its distribution in the profile of clayey Oxisols were studied to evaluate the role of the soil as a sink or source of atmospheric CO2 in the center of the cerrado region, Federal District, Brazil. Evaluations were carried out in six different management systems: a native cerrado type vegetation (CE), eucalypt reforestation (EU), introduced pasture (PA), heavy disk harrow tillage (GP), disk plow tillage (AD), no-tillage (PD), all of them having been established for more than twelve years. Organic carbon was analyzed in soil samples taken at a 100 cm depth. Carbon storage in all other five agroecosystems was compared to CE in order to analyze soil behavior as a source or sink of C-CO2. The main important dynamic features related to C, such as additions and losses, were observed in the upper soil layers. Compared with CE, the agroecosystems without soil disturbance like PD, PA and EU showed higher carbon accumulation, thus working as a soil sink for atmospheric C-CO2. Those with soil disturbance (AD and GP) showed lower carbon accumulation, thus working as a source of C to the atmosphere.