Sampling depth of soil and roots and Oryzophagus oryzae em cultivares de arroz

• Published in: Ciência rural 2011-12, Vol.41 (12), p.2039
• Main Authors: das Neves, Marcio Bartz, Ma, Grutzmacher, Anderson Dionei, de Lima, Crislaine Alves Barcellos, Buttow, Germano Tessmer
• Format: Article
• Language: Spanish
• Subjects: Rice; Weevils
• ISSN: 0103-8478

Oryzophagus oryzae is the key insect pest in flooded rice fields in southern Brazil Their larvae, known as rice water weevil cause significant yield losses when they cut the roots of rice plants. For the monitoring and survey of the larval population of O. oryzae, on rice fields and rice trials, respectively, are currently used standard samples of soil and roots, with 8.5cm deep and 10cm wide, blown away by submersion and shaking in a sieve with water for the counting of larvae. The visualization of larvae, especially the 1st and 2nd instars, becomes difficult in the suspension formed by the soil samples with these dimensions and the water inside the sieves. Thus, an experiment was conducted in a Typic Albaqualf soil according to the Latin square design to determine a sampling depth of soil and roots that makes possible the capture and display a larger number of larvae in a smallest possible volume of soil, in different rice cultivars. The treatments consisted of six rice cultivars ('BRS Atalanta '; 'BRS Firmeza '; 'BRS Ligeirinho '; 'BRS Querencia'; 'BRS Sinuelo CL'; 'IRGA 417') and three depths (3, 6 and 9cm) for removing samples of soil and roots, every 10cm diameter. In the immediate withdrawal of samples, it was announced the number of larvae. Subsequently, in periodic evaluations, it was announced the number of adults emerged from samples kept intact in plastic buckets with water depth of 13, 16 and 19cm, covered by screened mesh fabric. It was detected a significant interaction between sampling depths and the rice cultivars 'BRS Sinuelo CL' and 'BRS Querencia' in the rate of infestation of larvae and adults of O. oryzae, respectively. In the case of both variables the number of insects per sample was significantly higher at 6 cm depth than at 3cm, an intermediate in 9cm. It was concluded that in Typic Albaqualf soil, samples (soil and rice roots) taken from a depth of 6cm are more effective to capture and visualize larvae of O. oryzae in suspension (soil and water) formed in the sieves used for counting larvae, and also for the collection of adults of this insect. Key words: Oryza sativa, rice water weevil, insect count, method, integrated pest management. Oryzophagus oryzae e o inseto-praga chave da cultura do arroz irrigado por inundacao na Regiao Sul do Brasil. Suas larvas, conhecidas por bicheira-da-raiz, causam perdas significativas de produtividade quando danificam o sistema radicular das plantas de arroz. No monitoramento da populacao larval