Understand the critical period of attack by the green-bellied stink bug in corn crops, based on the stages of plant development and pest, it is essential to adopt management at the right time, in order to prevent losses and ensure greater grain yield.
The critical period that defines the corn productivity potential is defined during the stages initial stages of plant development. In this way, the occurrence of stress at these times, such as water deficit, diseases, destruction of the leaf area, suction of plant sap, a physical and chemical impediment to the soil, may have great impact on crop grain yield.
O green belly bug, Dichelops melacanthus (Dallas) (Hemiptera: Pentatomidae), constitutes an important pest in different crops such as soybeans, corn, oats and wheat. At the corn (zea mays L.), the damage resulting from the presence of this pest was registered for the first time in the Municipality of Rio Brilhante, in Mato Grosso do South, in 1993 (Ávila & Panizzi, 1995). It is believed that the intensification of second season corn cultivation (safrinha) and the increase in adoption of the direct planting system has provided favorable conditions for population increase of this pest in agricultural production systems in Brazil.
Populations of D. melacanthus have been observed in corn crops with damage to young plants, causing yellowing, lesions punctiform on the leaves and even tillering of the plants. The damages are caused by the insect feeding close to the seedling neck, where cause typical injuries as the leaves develop. Chocorosqui (2001) found that population densities from 2 bedbugs/m2 cause serious damage to the off-season corn crop. However, there are no studies that evaluated the damage potential of the green-bellied stink bug in different stages of development of the corn plant, as well as the potential of damage caused by the nymphs of this pest in the crop.
Na Embrapa Agricultural West research was conducted with the objective of evaluating the potential for damage caused by the green-bellied stink bug at different stages of development of corn plants, as well as the damage potential of different stages of development of this pest in corn plants.
To guarantee the supply of insects to conduct the tests, a bed bug farm was established green belly under laboratory conditions following the methodologies by Panizzi & Mourão (1999) and de Costa et al (1998).
The potential for harm from green-bellied stink bug at different stages of corn development was conducted under greenhouse and field conditions in 2015. field test, in a direct planting area, the opening of the furrows with approximately 4 corn seeds per meter at a spacing of 0,45 m between lines. The planting fertilizer was 250 kg/ha of fertilizer from the formulation 10-18-18 (N-P-K). Each sampling unit consisted of five plants corn, on which a cage was installed in a PVC coated structure with “tulle” fabric to contain insects. The treatments were represented by the different stages of the corn plant as follows: T1: plants with one leaf (V1); T2: plants with three leaves (V3); T3: plants with five leaves (V5); and T4: plants with seven leaves (V7). Each cage with different stages of corn was infested with five adult stink bugs during 14 days, except the control treatment (T5) in which there was no infestation of the bed bug since the V1 stage. The experimental design used was that of randomized blocks with five treatments (plant stages) and five repetitions (cage).
At the home rehearsal vegetation, the corn was sown in pots, taking a plant/pot to the first stage of bed bug infestation (V1). The treatments were same ones used in the field test (V1, V3, V5 and V7), where each pot with a corn plant was infested with an adult stink bug for fourteen days, covered with “tulle” fabric supported by a wire cage, for containment of insects on the corn plant. An additional treatment, in which there was no bedbug infestation, was also evaluated as a control. After the period of infestation, the bugs were eliminated from the plants, kept free of insects until determining the dry weight of the plants.
The trial that assessed the potential of damage caused by different stages of bed bug development green belly in corn was conducted in a greenhouse similar to the damage test at different stages of corn. The test was installed when the corn was at the V1 stage (an expanded leaf), and the plants were infested with 1 insect/vase that contained a corn plant. Four were studied bed bug development stages: T1: Small nymph (2nd instar), T2: medium nymph (3rd to 4th instar), T3: large nymph (5th instar) and T4: adult (with around 48 hours old) and T5: no bed bug infestation. The infestations were kept in the pots for 14 days, and the insects were returned to the cage when they died.
corn plants when infested in the V1 vegetative stage with medium nymphs and large nymphs of the green-belly bug showed damage rates similar to those observed on plants infested with adults, which were significantly larger than the rates found in plants infested with small or no nymphs. infestation (Figure 1). Damage rates on plants infested with nymphs medium, large and adults presented average values around 3, which results in plants with curled or tillered cartridge, while corn plants infested with small nymphs obtained an average index, below 1, characterizing low potential of damage to corn at this stage of insect development (Figure 1).
Corn Plants subjected to attack by small nymphs also had no reductions significant differences in the dry weight of the aerial part, when compared to plants not infested by bedbugs (Figure 2). It is believed that the oral apparatus less developed at this stage of bed bug development (small nymphs) whether possibly the key factor that explains the results obtained. The plants infested with medium, large and adult nymphs of the green-bellied stink bug had significantly reduced weight compared to infested plants with small nymphs or those not infested by the pest (Figure 2).
Regarding the test of stink bug damage in the field, it was found that stink bug infestations in corn with different stages of development had a significant effect on stem diameter, with this effect being more deleterious on infested plants in stages V1 and V3 (Table 1). No significant difference was observed for the stem diameter in infested plants at development stages V5 and V7, when compared to the control treatment in which there was no infestation of the Prague. Corn plants infested with the stink bug in the growing stages development V1 and V3 also had the lowest grain yields when compared to the control treatment. Plants infested at stage V1 showed productivity reduction of 50% when compared to the productivity of plants in the control treatment. These results show that young plants from corn (V1 to V3) are more sensitive to attack by the green-bellied stink bug than more developed plants, such as those aged after the V5 stage. Second Fancelli & Dourado (1997), V1 to V6 comprise the period in which the plant defines its productive potential, thus being these stages more susceptible to pest attack. Bianco (2004) also observed that plants subjected to the presence of the green belly bug between 2 days and 9 days after emergence (DAE) were more susceptible to attack compared to plants infested at 16 DAE.
The highest rates of Stink bug damage to corn plants has been observed when infestations were performed at development stages V1, V3 and V5 (Table 1). When the infestation of D. melacanthus he was carried out at stage V7, the damage values on corn plants were similar to those observed in the control treatment, showing that in this At this stage of development, corn is already tolerant to pest attack.
In the damage test conducted in a greenhouse, damage rates to corn plants were higher when the infestations were carried out in the growth stages V1 and V3 development, followed by the V5 stage (Table 2). In the infestation carried out at stage V7, the damage rates in corn plants did not differ of that observed in plants from the control treatment (without infestation), at similarity to the results observed in the field test (Tables 1 and two).
Already the dry mass of corn plants had a significant reduction in all stages of development at which bed bug infestation occurred when compared to the control treatment (Table 2). However, the lowest values of dry weight were observed when bed bug infestations were carried out in V1 and V3, once again showing that these are the stages with the greatest susceptibility to pest attack. Duarte et al (2015) observed that in density of 2 green belly bugs/corn plant between the stages of V1 and V5 development, reductions in the dry mass of the aerial part of plants were significant in relation to non-infested plants. However, these authors did not evaluate the V7 stage, in which this research found the lowest susceptibility to attack by the green-bellied bug (Table 2).
Based on the results obtained in this study, it can be infer that the medium, large and adult nymphs of D. melacanthus have great potential to cause damage in the initial stages of development of corn, which is not observed for small nymphs of this type. Prague. In addition, the corn development stages V1, V3 and V5 are more susceptible to attack by adults of the green-bellied stink bug, D. melacanthus, compared to the stadium V7, and under these conditions a pest attack can drastically affect the crop grain yield. In this way, the producer must guarantee a greater protection of corn against attack by the green-bellied stink bug in stadiums initial stages of plant development, especially between stages V1 to V3, to ensure less damage from this pest and, consequently, higher grain yield of culture.
Article published in issue 222 of Cultivar Grandes Culturas, November, 2017.
Receive the latest agriculture news by email
Receive the latest agriculture news by email
