Avaliação entomologica das plantas de cobertura nos sistemas de cultivo algodoeiro no Estado de Mato Grosso: Primeiros resultatos

'Real' direct sowing still raises numerous agricultural questions such as cover crop management, the possible rotations and fertilisation procedures. Few studies have been devoted to the impact of such systems on pests and their natural enemies, in particular in Mato Grosso State (Brazil). Entomological observations were made from January 2003 onwards in a cropping system set-up using cotton plants set out in 2001 at Fazenda Mourão, 30 km from Campo Verde-MT thanks to fi nancial support from the FACUAL fund, COODETEC and CIRAD. Different methods were used: beating trays, sweep nets, pitfall traps, synthesized pheromone traps and visual observation in soybean, cotton, maize and rice crops and in the cover plants Brachiaria ruziziensis and Eleusine coracana alone or combined with other plants. The observations revealed great differences in the phytosanitary situation from one farming season to another, with pests whose presence was constant ( Megascelis sp., dominant on soybean) or variable according to the year ( Nezara viridula , Spodoptera cosmioides ), the difficulty of making direct observations of physical transfers of fauna from one crop to another, the importance of measuring the impact of cover crops on polyphagous pests such as Spodoptera frugiperda , the need for good management of cotton stalk residues because of the risk of the spread of boll weevil and pink bollworm. On the a ssumption that genetically modified cotton plants will be developed soon, the knowledge about the entomofauna gained in this study will enable better definition of the impact on non- target organisms. (Résumé d'auteur