Distribution of eggs, larvae and adults of Sternechus subsignatus Boheman on soybean plants in no-till system Translated title: Distribuição de ovos, larvas e adultos de Sternechus subsignatus Boheman em plantas de soja em plantio direto

Abstract

Soybean [(Glycine max (L.) Merrill] commercial fields, maintained under a no-till system, were sampled during the crop seasons 1990/91 and 1996/97, in Cruz Alta and Júlio de Castilhos, Rio Grande do Sul State, to determine the distribution of eggs, larvae and adults of Sternechus subsignatus Boheman (Coleoptera : Curculionidae). Soybean plants and soil were examined at different time schedules. Eggs and larvae were recorded in main stems, lateral branches and leaf petioles, divided into the upper third, medium and lower third of soybean plants. Eggs (87%), and larvae (79%) were mainly observed in the main stem and in the medium plant sections (87% and 78%, respectively). Larval movement was not observed because larvae remained inside the galls, in the same area where the eggs were laid. Adults were located in different places depending on the sampling time. At night, adults were observed to move to the upper third of the plant and, during the day, down to the lower third of the plant and to the soil. The insects are normally concealed during their pre- and post- embryonic stage throughout most of the day.

Translated abstract

Estudou-se a localização e a distribuição de ovos, larvas e adultos de Sternechus subsignatus Boheman (Coleoptera: Curculionidae) em plantas de soja [(Glycine max (L.) Merrill] e no solo, em diferentes horários do dia, em lavouras comerciais no sistema plantio direto, entre as safras agrícolas de 1990/91 a 1996/97, em Cruz Alta e Júlio de Castilhos (RS). Ovos e larvas foram encontrados na haste principal, nos ramos laterais e nos pecíolos, nas partes superior, mediana e inferior das plantas. Não se verificou movimento das larvas para as partes mais altas ou mais baixas das planta à medida que se desenvolveram. Ovos (90%) e a maioria das larvas (87%) foram encontrados na haste principal e na parte mediana das plantas (79% e 78%, respectivamente). Adultos foram encontrados no terço superior, médio e inferior das plantas e no solo, em todos os horários de coleta. Verificou-se movimentação dos adultos para as partes mais altas das plantas durante a noite, e para as partes mais baixas das plantas e para o solo, durante o dia. Esses resultados evidenciam que a maioria dos ovos e das larvas fica protegida no interior da haste principal e na parte mediana das plantas, sob a folhagem. Adultos, durante o dia, ficam escondidos nas partes mais baixas das plantas, entre as folhas e no solo.