Green-bellied stink bug control tactics in corn

The Central-West region is responsible for a large part of corn production in Brazil. The intensification of second-season cultivation (off-season), as well as crop rotation and succession, have significantly modified production systems and phytosanitary management in corn, leading to changes in the composition and abundance of insect species that occur there. The use of the direct planting system has also favored the development and survival of some pests, such as phytophagous stink bugs, which can cause damage to off-season corn crops if not controlled.

Phytophagous bugs of the Pentatomidae family are sucking insects whose main characteristic is the habit of introducing their stylets into the feeding substrate, attacking various plant structures, although seeds and fruits are the preferred places for their feeding. In the Central-West region, safrinha corn is cultivated after the soybean harvest, a condition that favors the survival and multiplication of the green-bellied stink bug, Dichelops melacanthus, whose population can cause significant damage to the crop, especially in its initial stages of development. However, the relationship between damage to the corn plant and the presence of the green-bellied stink bug, as well as its level of economic damage to the crop, have been little studied in Brazil. This information, when identified, can provide support for the integrated management of this pest in corn crops, providing guidance on the ideal time to use control measures.

Greenbelly damage experiment in corn

 At Embrapa Agropecuária Oeste, research was carried out to evaluate the productive behavior of off-season corn in the presence of the green-bellied stink bug at different stages of plant development, as well as analyzing the effect of different population levels of this pest on the crop, to estimate its level of economic damage. This experiment was conducted in a greenhouse, using the Exceller cultivar, which was sown in plastic pots with a capacity of 13L containing soil, with two corn plants/pot. The plants were infested with four adults of the green-bellied stink bug at five different stages of development: V1 (one leaf); V2 (two leaves); V3 (three leaves); V4 (four leaves) and V5 (five leaves). An iron frame covered with filo-type fabric was placed on the plants in each pot to contain the insects during the infestation period (ten days). The pots were inspected daily to replace any dead bedbugs inside the cages. The experimental design was completely randomized with six treatments (five stages with infestation and a control without insects) in seven replications (pots with two plants). The corn plants were taken until harvest to determine the dry mass of the aerial part and grain yield. All corn plants received the necessary agricultural treatments as well as irrigation, when necessary. The data obtained were subjected to analysis of variance and the means compared using the Tukey test at 5% significance.

D. melacanthus damage level experiment

The experiment was carried out in the Embrapa Agropecuária Oeste area, in Dourados, Mato Grosso do Sul. Sowing was carried out in February, following the technical fertilization recommendations for the crop. The experimental unit consisted of an iron frame cage measuring 1m long by 0,90m wide and 0,90m high covered with nylon mesh, which covered five corn plants and a useful plot area of ​​0,90m2. When the plants were at the V1 stage (one leaf), they were infested with different population levels of D. melacanthus adults (zero, two, four, six and eight stink bugs/cage) for a period of ten days. The cages were inspected daily to replace any dead bedbugs inside. The experiment was conducted in a randomized block design with five treatments (infestation levels) and five replications (cages). After the infestation period, the stink bugs and cages were removed from the experimental units and the corn plants were periodically sprayed with insecticides to eliminate possible infestations of stink bugs or other pests. The test was carried out until harvest to determine the weight of the ears, the weight of 100 seeds and the grain yield. The results were subjected to analysis of variance and the treatment means were compared using the Tukey test at 5% significance.

To determine the level of damage, the data were subjected to regression analysis, with grain yield being the dependent variable and stink bug population densities being the independent variable. To calculate the level of economic damage (D), the formula suggested by Nakano was used. et al. (1981), %D = 100 x Ct/V, with Ct being the control cost and V being the value of the crop. The cost of stink bug control for corn crops was considered equivalent to R$ 84,08 per hectare, corresponding to an application of the insecticides imidacloprid + thiodicarb (45 + 135 g/ha) on the seeds and a spray with imidacloprid + betacyfluthrin (75 + 9,4 g/ha) on the plants.

Damage results

At all stages of development in which corn plants were infested with the green-bellied stink bug, lower values ​​of dry mass of the aerial part were observed, when compared to the dry mass of plants that were not infested with the stink bug. This effect was significantly more harmful in plants that had only one leaf (Figure 1) and shows that the injury caused by the stink bug in corn affected the accumulation of dry matter in the plant.

The green-bellied stink bug also reduced corn grain yield for infestations carried out on plants at stages V1, V2 and V3, when compared to plants not infested in the control treatment (Figure 2). In plants at stages V4 and V5, no significant reductions in grain yield were observed, although the productivity levels in these treatments were more than twice as low as the production observed in non-infested plants (without infestation).

In the ears that the corn plant will eventually produce, the kernels are generally formed up to the V3/V4 stage. With this, the maximum number of grains or potential production of this crop will be defined up to these stages of development. Therefore, the stink bug attack in the initial stages of corn development negatively interfered with the physiological development of the plants and, consequently, affected their grain yield potential.

Damage Level Results

The weight of 100 corn grains was not influenced by the stink bug population densities used in the cages. However, in the two highest stink bug population densities tested (six and eight stink bugs/cage), the weight of ears produced per cage was significantly reduced when compared to non-infested plants, although these did not differ statistically from densities of two and four. bedbugs/cage (Table 1). In the grain filling phase, the plant begins to transform sugars into starch, thus contributing to the increase in dry weight. This increase occurs due to the translocation of photoassimilates produced in the leaves to the ears and grains that are being formed. Based on the results obtained, it can be inferred that corn productivity was possibly affected by stink bug attack in the initial stages of plant development (V1), when there was a reduction in development and grain formation on the cob.

The yield of corn grains showed a negative and significant relationship with the levels of stink bug infestation in plants, since the increase in the population density of the green-bellied stink bug reduced the grain yield of the crop, and this relationship was significantly adjusted to the linear model. regression analysis (Figure 3). Through the estimated corn production values, for different population densities of the stink bug in the range of two to eight insects/cage, it was possible to estimate the grain yield per hectare. These grain yield values, when compared with those observed in the control (non-infested plants), made it possible to calculate the percentage of losses for each stink bug population density studied. The equation that related stink bug population densities and grain yields showed a 5,98% reduction in corn production for each stink bug added to the cage. Transforming the loss data for each insect/m2, it was estimated that one stink bug/m2 would cause a reduction of approximately 5,38% in corn grain production.

Using the formula suggested by Nakano et al. (1981), the percentage of damage (% D) in corn was determined, which is equivalent to the level of economic damage corresponding to 3,12% of production. Once this percentage of damage was known, a simple rule of three was established between the percentage of damage caused by the different population densities of the bed bug/cage and the percentage of damage obtained with the previously mentioned formula. In this way, it was found that the number of stink bugs that caused damage equivalent to the cost of their control (R$ 84,08), which represents the Economic Damage Level of the pest for corn crops, was 0,58 stink bug/ m2, considering an average crop grain yield of 6,568kg/ha.

The results obtained in this work showed a high potential for damage by the green-bellied stink bug in corn crops, with the level of economic damage found to control this pest being less than one stink bug/m². It should be noted that damage level calculations may vary from year to year, depending on the stage of the plant at which the stink bug infestation occurs, the level of productivity of the crop, the degree of susceptibility of the cultivar, as well as the cost of control used. for this plague on culture. The information obtained in this research will serve to guide decision-making for the implementation of tactics to control the green-bellied stink bug in corn crops.

Crébio José Ávila, Embrapa Agropecuária Oeste; Paulo Henrique Ramos Fernandes, Ivana Fernandes da Silva, Federal University of Grande Dourados