Predatory ants, play an important role for the functioning of ecosystems as they provide several essential ecosystem services. In their role as natural enemy of many pest insects, they positively impact agroecosystems. In Brazilian sugarcane plantations these ant species are the main predators of eggs and initial instar larvae of the sugarcane borer, Diatraea saccharalis (Lepidoptera: Crambidae), one of the key pests of this crop. Thus, the conservation of the predaceous ant fauna turns out to be a desirable, but at the same time challenging task. In this highly anthropized environment, ant populations are continuously impacted by the widespread application of insecticides used to control D. saccharalis and other sugarcane pests. Further, entomopathogenic fungi are used within integrated pest management and Beauveria bassiana has proven to be efficient in controlling D. saccharalis. However, a variety of previous studies showed, that the control of pest ants, using fungal entomopathogens, did not lead to satisfactory results. Thus, the use of B. bassiana could be an interesting and sustainable alternative to control D. saccharalis as this control strategy seems to preserve the ants. In this context, the purpose of the following study was to evaluate the impact on D. saccharalis and predatory ant populations after exposure to thiamethoxan + lambda-cialotrina, a systemic insecticide, or to B. bassiana, an entomopathogenic fungus. The experiment was conducted under field conditions in two different commercial sugarcane plantations located in the state of São Paulo, Brazil. The total experimental area of 2.500 m2 was divided into three equal plots, two treatment and one control area. The exposure of the insect populations to the treatments occurred by terrestrial pulverization, applying the product with the jet directed to the base of the plant (70% base / 30% soil), using thiamethoxan + lambda-cialotrina (141 / 106 g L-1) or B. bassiana (1 x 1011 conidia mL-1) as a suspension with 150 or 200 L of water, respectively. The population dynamics had been observed and assessed during a period of 40 to 69 days after application by weekly sampling of ants in pitfall- and sardine bait traps, and evaluation of the pest infestation based on the infestation intensity index. Further, anthill activity was monitored and assessed in each plot. The results showed that both products reduced the pest populations but did not cause a direct impact on the populations of predatory ants. Despite this, in all plots, including the control, we observed a heavy decline of the ant populations, verified by a continuous drop in the number of insects captured in the traps and the reduction of the anthill activity. We discussed the biotic and abiotic factors that could have been responsible for the population decline of the pest and its natural enemy. To support the results of the main experiment, complementary essays had been installed in a third experimental area, where the ants had been exposed to the same treatments. After application of the products, the area was artificially infested with the pest. The low damage incidence observed in all plots suggests predation, particularly as the presence of foraging ants had been verified, while looking for incidences of the pest on the plants. Hence, we suspect, that the decline of the ant populations in the main experiment seems somehow to be related to habitat conditions such as distribution and availability of food sources. As formigas predadoras desempenham um papel importante para o funcionamento dos ecossistemas, pois fornecem diversos serviços ecossistêmicos essenciais. Na sua função como inimigo natural de muitos insetos-praga, elas impactam positivamente os agroecossistemas. Em cana-de-açúcar, no Brasil, essas espécies são as principais predadoras de ovos e larvas da broca-da-cana, Diatraea saccharalis (Lepitoptera: Crambidae), uma das principais pragas dessa cultura. Diante disso, a conservação da fauna mirmecológica torna-se uma tarefa desejável, mas ao mesmo tempo desafiadora, uma vez que nesse ambiente altamente antropizado, as populações de formigas são continuamente impactadas pela aplicação de inseticidas para o controle de D. saccharalis e outras pragas da cana-de-açúcar. Além disso, fungos entomopatogênicos, são aplicados em programas de manejo integrado de pragas e Beauveria bassiana tem mostrado boa eficácia no controle de D. saccharalis. No entanto, diversas pesquisas conduzidas no passado mostraram que o uso desse fungo para o controle de diversas formigas-praga não levou a resultados satisfatórios. Diante disso, o uso de B. bassiana poderia ser uma alternativa interessante e sustentável para o controle de D. saccharalis, visto que, esta estratégia de controle parece preservar as formigas predadoras. Nesse contexto, o objetivo dessa pesquisa foi avaliar o impacto sobre as populações de D. saccharalis e formigas predadoras após exposição ao inseticida sistêmico tiametoxam + lambda-cialotrina e ao fungo entomopatogênico B. bassiana. O experimento foi conduzido em campo em duas diferentes áreas comerciais de cana-de-açúcar do estado de São Paulo, Brasil. A área total do delineamento experimental de 2.500 m2 foi dividida em três parcelas iguais, duas de tratamento e uma de controle. A exposição das populações dos insetos aos tratamentos ocorreu por meio de pulverização terrestre, aplicando-se o produto com jato direcionado à base da planta (70% base / 30% solo), utilizando tiametoxam + lambda-cialotrina (141 / 106 g L-1) ou conídios de B. bassiana (1 x 1011 conídios mL-1) em 150 e 200 mL de água respectivamente. A dinâmica populacional foi observada e avaliada durante um período de 40 a 69 dias após a aplicação, por amostragem semanal de formigas em armadilhas do tipo “pitfall” e com isca de sardinha. A infestação pela praga foi avaliada com base no índice de intensidade de infestação. Além disso, a atividade dos formigueiros foi monitorada e avaliada em cada parcela. Os resultados mostraram que os dois produtos diminuíram as populações da praga, porém não causaram um impacto direto nas populações das formigas predadoras. Não obstante disso, observou-se em todos os tratamentos, incluindo a testemunha, um forte declínio populacional de formigas, pela queda contínua no número de insetos capturados em armadilhas e pela redução na atividade dos formigueiros. Os fatores bióticos e abióticos que poderiam ter sido responsáveis pelo declínio populacional da praga e seu inimigo natural foram discutidos. Para apoiar os resultados do experimento principal, ensaios complementares foram instalados em uma terceira área experimental, onde as formigas foram expostas aos mesmos tratamentos e a praga infestada artificialmente. A baixa incidência de danos observada em todas as parcelas sugere que houve predação, porque foi verificada presença expressiva de formigas forrageando na parte aérea das plantas, enquanto procurava-se pela praga nas plantas. Portanto, suspeita-se que o declínio das populações de formigas no experimento principal está relacionado às condições do habitat, particularmente à distribuição e disponibilidade de fonte de alimentos. Palavras-chaves: Formigas predadoras; Diatraea saccharalis; inseticidas neurotóxicos e sistêmicos; Beauveria bassiana; relações tróficas. Predatory ants, play an important role for the functioning of ecosystems as they provide several essential ecosystem services. In their role as natural enemy of many pest insects, they positively impact agroecosystems. In Brazilian sugarcane plantations these ant species are the main predators of eggs and initial instar larvae of the sugarcane borer, Diatraea saccharalis (Lepidoptera: Crambidae), one of the key pests of this crop. Thus, the conservation of the predaceous ant fauna turns out to be a desirable, but at the same time challenging task. In this highly anthropized environment, ant populations are continuously impacted by the widespread application of insecticides used to control D. saccharalis and other sugarcane pests. Further, entomopathogenic fungi are used within integrated pest management and Beauveria bassiana has proven to be efficient in controlling D. saccharalis. However, a variety of previous studies showed, that the control of pest ants, using fungal entomopathogens, did not lead to satisfactory results. Thus, the use of B. bassiana could be an interesting and sustainable alternative to control D. saccharalis as this control strategy seems to preserve the ants. In this context, the purpose of the following study was to evaluate the impact on D. saccharalis and predatory ant populations after exposure to thiamethoxan + lambda-cialotrina, a systemic insecticide, or to B. bassiana, an entomopathogenic fungus. The experiment was conducted under field conditions in two different commercial sugarcane plantations located in the state of São Paulo, Brazil. The total experimental area of 2.500 m2 was divided into three equal plots, two treatment and one control area. The exposure of the insect populations to the treatments occurred by terrestrial pulverization, applying the product with the jet directed to the base of the plant (70% base / 30% soil), using thiamethoxan + lambda-cialotrina (141 / 106 g L-1) or B. bassiana (1 x 1011 conidia mL-1) as a suspension with 150 or 200 L of water, respectively. The population dynamics had been observed and assessed during a period of 40 to 69 days after application by weekly sampling of ants in pitfall- and sardine bait traps, and evaluation of the pest infestation based on the infestation intensity index. Further, anthill activity was monitored and assessed in each plot. The results showed that both products reduced the pest populations but did not cause a direct impact on the populations of predatory ants. Despite this, in all plots, including the control, we observed a heavy decline of the ant populations, verified by a continuous drop in the number of insects captured in the traps and the reduction of the anthill activity. We discussed the biotic and abiotic factors that could have been responsible for the population decline of the pest and its natural enemy. To support the results of the main experiment, complementary essays had been installed in a third experimental area, where the ants had been exposed to the same treatments. After application of the products, the area was artificially infested with the pest. The low damage incidence observed in all plots suggests predation, particularly as the presence of foraging ants had been verified, while looking for incidences of the pest on the plants. Hence, we suspect, that the decline of the ant populations in the main experiment seems somehow to be related to habitat conditions such as distribution and availability of food sources. Keywords: Predatory ants; Diatraea saccharalis; neurotoxic and systemic insecticides; Beauveria bassiana; trophic relationships.