Impacto de tiametoxam + lambda-cialotrina e Beauveria bassiana sobre populações de formigas predadoras e da broca-da-cana, Diatraea saccharalis (Lepidoptera: Crambidae), em cana-de-açúcar

• Autor(a) principal: Weise, Claudia
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional do FGV (FGV Repositório Digital)
• Texto Completo: https://hdl.handle.net/10438/30333
• topic: Predatory ants; Diatraea saccharalis; Neurotoxic and systemic insecticides; Beauveria bassiana; Trophic relationships; Formigas predadoras; Diatraea saccharalis; Beauveria bassiana; Relações tróficas; Inseticidas neurotóxicos e sistêmicos; Economia; Inseticidas - Pesquisa; Pragas agrícolas; Produtos químicos agrícolas - Aspectos ambientais; Formiga

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.