Ciências Biológicas e da Saúde
URI permanente desta comunidadehttps://locus.ufv.br/handle/123456789/3
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Item Physiological and molecular basis of spatial repellency mediated by pyrethrum and pyrethroids in Aedes-aegypti(Universidade Federal de Viçosa, 2021-02-12) Andreazza, Felipe; Oliveira, Eugênio Eduardo de; http://lattes.cnpq.br/2992672572696736Aedes aegypti mosquitoes are vectors of several viruses, such the ones causing Dengue and Yellow fevers, Chikungunya and Zika. Thus, compounds that can repel mosquitoes are used to prevent human-mosquito contact, aiding the fight against vector-borne diseases. Pyrethrum and its synthetic analogs, pyrethroids, are widely used for this purpose. However, the physiological and molecular mechanism of their spatial repellency (i.e., non-contact repellency) have not yet being deciphered. In this thesis, I bring two major contributions to the field, divided into two chapters. In the chapter 1, I present a continuing effort for understanding pyrethrum spatial repellency. As previous studies had shown that the activation of the odorant receptor (Or) protein AaOr31 by a minor component of pyrethrum [i.e., E)-β-farnesene (EBF)] only partially explain the pyrethrum repellency, I showed that pyrethrins I and II, the major components of this extract, elicit repellency by acting in two targets, the voltage-gated sodium channels and an Or expressed in a specific sensilla (i.e., sst-1) in Ae. aegypti antenna. Interesting, I also discovered that pyrethrins action on the voltage-gated sodium channels are responsible for enhancing the EBF repellency, explaining why EBF plays a role in pyrethrum repellency even at minute concentrations. In the chapter 2, I bring a contribution toward understanding the spatial repellency by transfluthrin, one of the main pyrethroids being recently deployed as mosquito repellent. Similarly to pyrethrins, transfluthrin elicits repellency by acting on the voltage-gated sodium channel. However, transfluthrin could not activate any neuron in mosquito major sensing appendages, as well as its repellency does not in-volve activation of any Or. Transfluthrin also enhances repellency of other Or-dependent repellents, including the gold-standard repellent DEET. In fact, I discovery that samples of commercial transfluthrin-based mosquito repellents elicit Or-mediated repellency, even though transfluthrin does not act on Ors. Together, these chapters illustrate that humans have been unknowingly exploiting this dual target synergistic mechanism for insect repellency for centuries, and that single action on voltage-gated sodium channels is sufficient to elicit repellency in Ae. aegypti. These results should inspire new chemistries toward volatile compounds acting on sodium channels and development of potent multi-target mixtures. The reduction in the concentration of individual components when in a mixture is expected to decrease environment contamination, and allergies, such as caused by high concentrations of DEET. There- fore, this new framework to be exploited promotes environmental and social sustainability, and aid the control of deadly vector-born human diseases. Keywords: Mosquitoes. Vector-borne diseases. Behavior. Voltage-gated sodium channels. Odorant receptors. Synergism.Item Occurrence reports and insecticide susceptibility in Drosophila suzukii populations from Brazilian Southeast Region(Universidade Federal de Viçosa, 2017-07-17) Andreazza, Felipe; Oliveira, Eugênio Eduardo de; http://lattes.cnpq.br/2992672572696736Early monitoring and toxicological studies with invasive pest species, such as the Spotted Wing Drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), are of importance. It took only about 3 years to D. suzukii become the worldwide most important pest of small soft-skinned fruits, such as strawberries, blueberries and cher- ries. This drosophilid lays its eggs inside undamaged fruits, and its larvae destroy the fruit tissues, making it unmarketable. While attention was driven to the search about D. suzukii bioecology and alternative control tools, the spray with broad-spectrum insecticides has being the most used emergency control strategy, increasing the proba- bility of insecticide resistance selection in this species. Thus, in the current study, field surveys were performed aiming to identify and report the arrival/presence of the D. suzukii in two Brazilian states. Then, preliminary insecticide susceptibility compar- isons were carried out on populations originally collected in these regions to evidence potential resistance sources. Finally, it was assessed the toxicity of lime-sulfur (i.e. an old alternative pesticide) on D. suzukii and its oviposition and development on sprayed strawberry plants. The field surveys demonstrated that D. suzukii is already present in both Minas Gerais (MG) and Espírito Santo (ES) states. The species was first collected in a strawberry field at the municipality of Ervália - MG in March of 2016 and in Juiz de Fora - MG in November of 2016. Later, in February of 2017, the species was also found infesting strawberry and blackberry fields at the municipal- ities of Domingos Martins and Santa Maria de Jetibá - ES. In the blackberry fields, the infestation of D. suzukii occurred simultaneously with its confamiliar, Zaprionus indianus Gupta (Diptera: Drosophilidae). The susceptibility comparisons among D. suzukii populations identified a potential source of resistance to imidacloprid in a pop- ulation originally collected at the municipality of Juiz de Fora - MG (P < 0.05), while no consistent differences among populations were found for permethrin (P > 0.05). Lime-sulfur was toxic (LC50 = 26.6 mL/L) to D. suzukii flies in low concentrations, and its spray on strawberry plants reduced the D. suzukii oviposition in both choice (48.6% of reduction) and no choice (47.6% of reduction) semi-field bioassays (P < 0.05). It was also found a slight delay in the pre-imaginal developmental time of individuals from eggs laid on lime-sulfur treated plants only in the choice bioassay, indicating a possible effect of the females oviposition choice on its offspring development. Two other alternative preparations based in mixture of sulfur, lime, potassium perman- ganate, salt and detergent and the insecticides azadirachtin and indoxacarb did not cause high D. suzukii mortalities. As conclusions, D. suzukii has extended its current distribution range in Brazil, with presence of resistance sources to imidacloprid. Alter- natives, such as lime-sulfur, might be recommended in rotations for both traditional and organic farming approaches. Further studies monitoring the occurrence of insec- ticide resistance in field populations, as well as better investigation of the sublethal effects and compatibility of lime-sulfur applications on other D. suzukii hosts should be performed.