Danos dos percevejos Dichelops melacanthus na soja e Euschistus heros no milho, em dois estádios de desenvolvimento das culturas

Abstract

Brazilian Agribusiness is responsible for 21.8% of the national gross domestic product and among the species cultivated on a large scale, soybean and corn crops stand out. However, the different changes that occurred in the agricultural scenario, many species of phytophagous stink bugs found favorable conditions for their feeding and development, becoming important pests in these crops, mainly in the reproductive stage in soybeans and early stages of development in maize. The aim of this study was to evaluate the potential damage of stink bugs Dichelops melacanthus (Dallas) on soybean and Euschistus heros (Fabricius) on maize. The trials were carried out during the 2019/2020 crop season, evaluating six population levels of D. melacanthus on soybean and E. heros on maize, in two stages of crop development. It were assayed population levels of stink bug in the cages (0, 2, 4, 6, 8 and 10) in the development stages V2 and V1 of soybean and maize, respectively. In two other trials were evaluated the population levels of stink bug in the cages (0, 3, 6, 9, 12 and 15) in the development stages R5.1 and V4 of the soybean and maize, respectively. The experimental design was randomized block in both trials. The experimental units in the soybean trials consisted by cages installed in the field, with 20 plants per cage, while in maize crop consisted of 5 plants per cage. The cages were daily verified after infestation, which the dead insects were replaced. The infestantions were maintained during 14 days. After the removal of the cages in the first soybean trial (V2) it was determined the plant stand while grain yield and thousand grain weight in harvest. The soybean infested in R5.1 development stage, it were evaluated grain yield, thousand grain weight and seed quality by the tetrazolium test. In maize, it was characterized the plant injury after the removal of the cages, the mensuration of the stem diameter and grain yield. Infestations with D. melacanthus at V2 development stage of soybean did not interfere in the crop plant stand or grain yield and thousasnd grain weight, even with increase in the population levels of the stink bug. When the infestations were carried out at the R5.1 stage, there was also no significant effect on grain yield and on the soybean thousand grain weight. However, the increase of D. melacanthus populations at R5.1 stage reduced the germination potential, the seed vigour, as well as significantly increased the percentage of seed sucked and non-viable seeds. In maize, infestations carried out in stage V1 with the stink bug E. herosresulted in increased damage to the crop, as well grain yield was reduced with increment insect population densities per cage. However, the increase in the density of the stink bug did not affect the diameter of the maize stem. Infestations of the bug E. heros carried out at the V4 stage of maize, it did not affect the intensity of damage to the plants, the grain yield and stem diameter. It was concluded that the occurrence of the bug D. melacanthus is important only in the reproductive phase of the soybean, when the control of this pest needs to be carried out to avoid losses in the quality of the seeds. On the other hand, in maize crop, the period of greatest susceptibility of plants to the E. heros stink bug is at V1 stage, requiring the monitoring and control of this pest to avoid a reduction in grain yield, differently from what was observed for infestations carried out at the V4 stage of development, when grain yield was not affected.