Path Analysis between Pest Occurrence and Nutritional Status of Soybean under Phosphate Fertilization.

BACKGROUND AND OBJECTIVE: The phytophagous insects select their host plants according to plant tissue nutritional quality. Thus, the objective of this study was to correlate the direct and indirect effects of phosphate fertilization on the nutritional status of the soybean crop and its relationship with the occurrence of insect pests. MATERIALS AND METHODS: The effect of phosphate fertilization on soybean was evaluated using two phosphate sources, Single Superphosphate (SSP) and Monoammonium Phosphate (MAP), applied at five rates of P2O5. A sampling of insects initiated from stage V5 and was done weekly. Leaves were collected for nutrient analysis stage R1, in stage R9 was harvest was carried out. SSP or MAP phosphate fertilization in soybean affected the incidence of Chrysodeixis includens, Helicoverpa armigera, Elasmopalpus lignosellus and Euschistus heros. RESULTS: The plants treated with MAP had the infestation reduced compared with plants treated with SSP. Higher contents of Cu and Fe in the leaf reduces the incidence of insect-pests, whereas the opposite occurred with Mn. The occurrence of E. lignosellus reduced soybean yield. CONCLUSION: Therefore, the source and rates of phosphorus in soybean fertilization change the concentration of macro and micronutrients in the leaves and affect the behavior and incidence of pest species.

Toxicidade de extratos de Anadenanthera macrocarpa (Fabaceae: Mimosoideae) e Bougainvillea buttiana (Nyctaginaceae) para lepidópteros-praga / Toxicity of extracts of Anadenanthera macrocarpa (Fabaceae: Mimosoideae) and Bougainvillea buttiana (Nyctaginaceae) for lepidoptera-pest

O uso de extratos vegetais apresenta grande eiciência no manejo de pragas, destinados a produções agrícolas de pequeno e médio porte, por controlar uma gama muito grande de artrópodes. O objetivo desta pesquisa consiste em avaliar os efeitos tóxicos dos extratos de Anadenanthera macrocarpa (Fabaceae: Mimosoideae) e Bougainvillea buttiana (Nyctaginaceae) em Helicoverpa armigera (Hübner), Spodoptera cosmioides (Walker) e Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). Lagartas de H. armigera e S. cosmioides foram mantidas em discos foliares de soja, enquanto S. frugiperda foi mantida em discos foliares de milho, tratados com os extratos aquoso diluídos nas concentrações de: 0, 500, 1.000, 2.500, 4.000, 5.000, 10.000 e 15.000 mg.L-1. Foram mensurados os efeitos letais e subletais dos extratos sobre os insetos. De acordo com os resultados obtidos, a concentração de 500 mg.L-1 do extrato de A. macrocarpa causou o maior percentual de mortalidade (93,33%) em H. armigera. O extrato de B. buttiana causou 86,67% e 60% de mortalidade em H. armigera (1.000 mg.L-1) e S. cosmioides (4.000 mg.L-1), respectivamente. A redução da emergência dos adultos foi o principal efeito subletal constatado em S. cosmioides e S. frugiperda. Considerando os resultados obtidos, destaca-se que os extratos vegetais utilizados apresentam-se como uma alternativa em potencial para o manejo de lepidópteros-praga.

For small and medium agricultural production, vegetal extracts are highly eficient at managing pests because they control a wide range of arthropods. The objective of this research was to evaluate the toxic effects of Anadenanthera macrocarpa (Fabaceae: Mimosoideae) and Bougainvillea buttiana (Nyctaginaceae) extracts on Helicoverpa armigera (Hübner), Spodoptera cosmioides (Walker) and Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). Helicoverpa armigera and S. cosmioides caterpillars were maintained on soybean leaf discs, and S. frugiperda was maintained on corn leaf discs, treated with diluted aqueous extracts at concentrations of 0, 500, 1,000, 2,500, 4,000, 5,000, 10,000 and 15,000 mg.L-1. The lethal and sublethal effects of the extracts on the insects were measured. According to the results, the concentration of 500 mg.L-1 of the A. macrocarpa extract caused the highest percentage of mortality (93.33%) of H. armigera. The extract of B. buttiana caused 86.67% and 60% mortality of H. armigera (1,000 mg.L-1) and S. cosmioides (4,000 mg.L-1), respectively. The reduction of the emergence of adults was the main sublethal effect found for S. cosmioides and S. frugiperda. Considering the results, the vegetal extracts used in this research are a potential alternative for the management of lepidopteran pests.