Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) in Peaches: is it a problem?

Healthy peach fruit is not considered a preferred host for Drosophila suzukii (Matsumura); however, it becomes a more preferable host when damaged. Thus, damaged peach fruit is of importance not only in terms of economic losses, but also because it serves as a reservoir for this fly species. This work aimed to evaluate the suitability of peaches mechanically damaged or harboring the brown rot disease as hosts for D. suzukii compared to hosts for which they have a low (undamaged peach) and high (undamaged strawberry) preference. Damaged peaches were as susceptible as undamaged strawberries. Fungus infection alone did not increase the susceptibility of peaches compared to undamaged peaches. This information should be considered when an Integrated Pest Management program is defined in a scenario of different species of fruit production

Population genomics of Drosophila suzukii reveal longitudinal population structure and signals of migrations in and out of the continental United States

Drosophila suzukii, or spotted-wing drosophila, is now an established pest in many parts of the world, causing significant damage to numerous fruit crop industries. Native to East Asia, D. suzukii infestations started in the United States (U.S.) a decade ago, occupying a wide range of climates. To better understand invasion ecology of this pest, knowledge of past migration events, population structure, and genetic diversity is needed. In this study, we sequenced whole genomes of 237 individual flies collected across the continental U.S., as well as several sites in Europe, Brazil, and Asia, to identify and analyze hundreds of thousands of genetic markers. We observed strong population structure between Western and Eastern U.S. populations, but no evidence of any population structure between different latitudes within the continental U.S., suggesting there is no broad-scale adaptations occurring in response to differences in winter climates. We detect admixture from Hawaii to the Western U.S. and from the Eastern U.S. to Europe, in agreement with previously identified introduction routes inferred from microsatellite analysis. We also detect potential signals of admixture from the Western U.S. back to Asia, which could have important implications for shipping and quarantine policies for exported agriculture. We anticipate this large genomic dataset will spur future research into the genomic adaptations underlying D. suzukii pest activity and development of novel control methods for this agricultural pes

A dual-target molecular mechanism of pyrethrum repellency against mosquitoes

Pyrethrum extracts from flower heads of Chrysanthemum spp. have been used worldwide in insecticides and repellents. While the molecular mechanisms of its insecticidal action are known, the molecular basis of pyrethrum repellency remains a mystery. In this study, we find that the principal components of pyrethrum, pyrethrins, and a minor component, (E)-β-farnesene (EBF), each activate a specific type of olfactory receptor neurons in Aedes aegypti mosquitoes. We identify Ae. aegypti odorant receptor 31 (AaOr31) as a cognate Or for EBF and find that Or31-mediated repellency is significantly synergized by pyrethrin-induced activation of voltage-gated sodium channels. Thus, pyrethrum exerts spatial repellency through a novel, dual-target mechanism. Elucidation of this two-target mechanism may have potential implications in the design and development of a new generation of synthetic repellents against major mosquito vectors of infectious diseases

Relatos de ocorrência e susceptibilidade à inseticidas em populações de Drosophila suzukii da região sudeste Brasileira

Early 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). 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). A calda sulfocálcica foi tóxica (CL50 = 26,6 mL/L) para D. suzukii em baixas concentrações, e a sua pulverização em plantas de morango reduziu a oviposição em bioensaios de semi-campo com chance de escolha (48,6% de redução) e sem chance de escolha (47,6% de redução) (P < 0.05). Verificou-se também um ligeiro atraso no tempo de desenvolvimento pré-imaginal dos indivíduos oriundos a partir de ovos colocados em plantas tratadas com a calda sulfocálcica apenas no bioensaio com escolha, indi- cando um possível efeito da escolha de oviposição das fêmeas no desenvolvimento de sua prole. Duas outras preparações alternativas à base de mistura de enxofre, cal, permanganato de potássio, sal e detergente e os inseticidas azadiractina e indoxacarb não causaram mortalidades elevadas de D. suzukii. Como conclusões, D. suzukii am- pliou sua atual faixa de distribuição no Brasil, com presença de fontes de resistência ao imidacloprido. Alternativas, como a calda sulfocálcica, pode ser recomendada em rotações para ambas as abordagens de agricultura orgânica e tradicional. Estudos adicionais que monitorem a ocorrência de resistência à inseticidas em populações de campo, bem como uma melhor investigação dos efeitos subletais e compatibilidade de aplicações de calda sulfocálcica em outros hospedeiros de D. suzukii devem ser realizados.Conselho Nacional de Desenvolvimento Científico e Tecnológic

Bases fisiológicas e moleculares da repelência mediada por piretro e piretróides em Aedes aegypti

Aedes 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.Mosquitos Aedes aegypti são vetores de vários vírus, como os que causam Dengue, Febre Amarela, Chikungunya e Zika. Assim, compostos que podem repelir mosquitos são usados para reduzir o contato dos mosquito com os humanos, auxiliando no combate à doenças transmitidas por vetores. O piretro e seus análogos sintéticos, os piretróides, são amplamente utilizados com essa finalidade. No entanto, o mecanismo fisiológico e molecular de sua repelência espacial (i.e., sem-contato) ainda não foi decifrado. Nesta tese, eu trago duas contribuições importantes para a área, divididas em dois capítulos. No capítulo 1, apresento um esforço contínuo para compreender a repelência espacial do piretro. Como estudos anteriores mostraram que a ativação do receptor odorante (Or) da proteína AaOr31 por um componente minoritário do piretro [i.e., (E)-β-farnesene (EBF)] explica a repelência do piretro apenas parcialmente, eu mostrei que as piretrinas I e II, os principais componentes desse extrato, provocam repelência agindo em dois alvos, os canais de sódio dependentes de voltagem e um Or expresso em uma sensila específica (i.e., sst-1) na antena de Ae. aegypti. Curiosamente, eu também descobri que a ação das piretrinas nos canais de sódio dependentes de voltagem são responsáveis por aumentar a repelência do EBF, explicando por que o EBF desempenha um papel na repelência do piretro, mesmo em concentrações mínimas. No capítulo 2, trago uma contribuição para a compreensão da repelência espacial pela transflutrina, um dos principais piretróides recentemente implementados como repelente de mosquitos. Igualmente às piretrinas, a transflutrina provoca repelência ao agir nos canais de sódio dependentes de voltagem. No entanto, a transflutrina não conseguiu ativar nenhum neurônio nos principais apêndices dos mosquitos, e sua repelência não envolve a ativação de nenhum Or. A transflutrina também aumenta a repelência de outros repelentes que agem em Or, incluindo o conhecido repelente DEET. De fato, descobri que amostras comerciais de repelentes de mosquitos à base de transflutrina provocam repelência mediada por Or, mesmo que a transflutrina não atue sobre Ors. Juntos, esses capítulos ilustram que os humanos têm explorado sem saber esse mecanismo sinérgico com alvo duplo para repelência a insetos por séculos, e que uma ação apenas nos canais de sódio dependentes de voltagem já é suficiente para provocar repelência em Ae. aegypti. Esses resultados devem inspirar novas químicas de compostos voláteis que atuem nos canais de sódio, e o desenvolvimento de misturas mais potentes. Espera-se que a redução na concentração de componentes individuais quando em uma mistura diminua a contaminação do meio ambiente e as alergias, como as causadas por altas concentrações de DEET. Portanto, esta nova estrutura a ser explorada promove a sustentabilidade ambiental e social e auxilia no controle de doenças humanas transmitidas por vetores. Palavras-chave: Mosquitos. Doenças transmitidas por vetores. Comportamento. Canais de sódio dependentes de voltagem. Receptores de odor. Sinergismo.Conselho Nacional de Desenvolvimento Científico e Tecnológic

Implications of Sublethal Insecticide Exposure and the Development of Resistance on Mosquito Physiology, Behavior, and Pathogen Transmission

For many decades, insecticides have been used to control mosquito populations in their larval and adult stages. Although changes in the population genetics, physiology, and behavior of mosquitoes exposed to lethal and sublethal doses of insecticides are expected, the relationships between these changes and their abilities to transmit pathogens remain unclear. Thus, we conducted a comprehensive review on the sublethal effects of insecticides and their contributions to insecticide resistance in mosquitoes, with the main focus on pyrethroids. We discuss the direct and acute effects of sublethal concentrations on individuals and populations, the changes in population genetics caused by the selection for resistance after insecticide exposure, and the major mechanisms underlying such resistance. Sublethal exposures negatively impact the individual’s performance by affecting their physiology and behavior and leaving them at a disadvantage when compared to unexposed organisms. How these sublethal effects could change mosquito population sizes and diversity so that pathogen transmission risks can be affected is less clear. Furthermore, despite the beneficial and acute aspects of lethality, exposure to higher insecticide concentrations clearly impacts the population genetics by selecting resistant individuals, which may bring further and complex interactions for mosquitoes, vertebrate hosts, and pathogens. Finally, we raise several hypotheses concerning how the here revised impacts of insecticides on mosquitoes could interplay with vector-mediated pathogens’ transmission

Toxicity to and egg‐laying avoidance of Drosophila suzukii (Diptera: Drosophilidae) caused by an old alternative inorganic insecticide preparation

The application of synthetic insecticides remains the most used tool for the management of spotted‐wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). However, management of this pest in the organic production of soft‐skinned fruits is a complex task due to the restricted number of registered products. Here, we assess the toxicity of lime sulfur and evaluate whether lime sulfur‐treated strawberry plants affected the oviposition and development of D. suzukii. Lime sulfur exhibited adequate toxicity to D. suzukii (LC50 = 26.6 mL L−1) without phytotoxicity to strawberry plants. When D. suzukii females were exposed to lime sulfur‐treated plants in no‐choice bioassays, oviposition was significantly (t‐test, P < 0.05) reduced compared with that on untreated plants. In free‐choice bioassays, D. suzukii females laid significantly (paired t‐test, P < 0.05) more eggs on untreated plants. Furthermore, in the free‐choice bioassays, immature development was slower for adults that originated from eggs laid on lime sulfur‐treated plants than from those laid on untreated plants. Lime sulfur showed adequate control and, therefore, has potential for use as a management tool against D. suzukii infestations in organic production systems. This old, alternative insecticide preparation not only caused adult fly mortality, but also reduced the number of eggs laid on lime sulfur‐treated plants

Toxicity to and egg‐laying avoidance of Drosophila suzukii (Diptera: Drosophilidae) caused by an old alternative inorganic insecticide preparation

The application of synthetic insecticides remains the most used tool for the management of spotted‐wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). However, management of this pest in the organic production of soft‐skinned fruits is a complex task due to the restricted number of registered products. Here, we assess the toxicity of lime sulfur and evaluate whether lime sulfur‐treated strawberry plants affected the oviposition and development of D. suzukii. Lime sulfur exhibited adequate toxicity to D. suzukii (LC50 = 26.6 mL L−1) without phytotoxicity to strawberry plants. When D. suzukii females were exposed to lime sulfur‐treated plants in no‐choice bioassays, oviposition was significantly (t‐test, P < 0.05) reduced compared with that on untreated plants. In free‐choice bioassays, D. suzukii females laid significantly (paired t‐test, P < 0.05) more eggs on untreated plants. Furthermore, in the free‐choice bioassays, immature development was slower for adults that originated from eggs laid on lime sulfur‐treated plants than from those laid on untreated plants. Lime sulfur showed adequate control and, therefore, has potential for use as a management tool against D. suzukii infestations in organic production systems. This old, alternative insecticide preparation not only caused adult fly mortality, but also reduced the number of eggs laid on lime sulfur‐treated plants