Green-bellied stink bug management

Successive soybean and corn crops have favored the occurrence of pests in Brazil, due to the constant supply of food in the crops. This is the case of the green belly bug, which causes damage to both crops. In addition to crops, weeds, such as trapoeraba, deserve special attention because they serve as hosts. Management of this insect needs to be carried out rationally and with great care, to prevent the worsening of resistance problems and preserve the scarce technologies available for control.

Soybean cultivation (summer crop) followed immediately by corn (second harvest: autumn-winter) is a production system widely used in Brazil, which has been favoring population growth and the permanence of some species of stink bugs in crops. Such an occurrence is justified due to the fact that these insects benefit from constant food supply (green bridge). There is a wide diversity of bed bugs that attack soybeans. Many migrate to second-crop corn cultivation when soybeans are being harvested. One example is the green-bellied stink bug. At soybean its occurrence is greater at the end of the reproductive phase and, in corn, already in the beginning of development due to the population that grew in the previous cultivation. In both cultures the damage can be significant. Therefore, research has been conducted at Embrapa Soja to improve management of the green-bellied stink bug taking into account the production system as a whole, which is one of the greatest challenges in the correct management of the pest.  

Various species of Stink bugs attack soybean crops and later migrate to soybean crops. corn grown in succession. Of these, the green-bellied stink bug (Figure 1A) deserves to be highlighted, despite generally being present a lower population than the brown stink bug (Figure 1B) (currently the most abundant species in the production system of soybeans). The green-bellied stink bug usually attacks corn at the base of the plant close to the ground. When this attack occurs in the first few weeks of development of the crop, there may be damage to the apical meristem, with deformation in plants. Differently, the brown stink bug prefers the top of the plants, sucking them closer to the cartridge, which provides attack with less potential for injury to corn plants. That's why it's great It is important for the farmer to differentiate the brown stink bug from the green-bellied stink bug (Figure 1), because while you need to worry more about the green-bellied stink bug in corn, the occurrence of the brown stink bug does not require the same care and the corn plant usually has a greater capacity to tolerate your attack. Differently, in soybean, both species cause the same damage to the plant.

The green-bellied stink bug belongs to the genus Dichelops, being the species Dichelops melacanthus e Dichelops furcatus the most important in Brazil. D. melacanthus is more common, as it covers a greater territorial extension than D. furcatus, focusing on the areas warmer agricultural areas of subtropical and tropical regions. In the north of Paraná D. melacanthus was the only species found in surveys carried out between 1998 and 2001. In contrast, in the Rio Grande do Sul D. furcatus and the most important species, as it is concentrated in areas with mild temperatures. These two species are very similar to each other and their common name is due to their the dorsal part of the body is brown and the ventral part is green (Figure 1A and 1C). However, in some situations of environmental stress, especially during the off-season, Green-bellied stink bug can present color variations, with an abdomen less greenish than usually found, and can be confused with brown stink bug. Therefore, it is important to observe the structure in the head between the antennas highlighted by red arrows in Figure 1C. While in the green-bellied stink bug it is forked, in the brown stink bug it is rounded.

Damage and management in the soy: corn system

O Green-bellied stink bug can occur throughout the soybean and corn cycle. However, the soybean plant tolerates stink bug attacks in the vegetative phase. without any reduction in productivity, therefore, any control measure at this stage of crop development. Unfortunately, some Farmers and technicians recommend the use of insecticides in the vegetative phase of soybeans for bed bug control with the aim of reducing their increase population in the reproductive phase of the crop. However, it is important to highlight that these insecticide applications, carried out in the vegetative phase, bring only harm to farming. Among the harms of the application advance of stink bug control in soybeans (in the growing season) stands out the selection of insects resistant to the insecticides used and the elimination of natural enemies.

All farmer knows how difficult it is to control bedbugs with insecticides currently available on the market. Among the causes are the occurrence of increasingly resistant populations. The development of resistance in bed bugs is due to the excessive use of insecticides to control them throughout of years. Therefore, due to the scarcity of different modes of action of insecticides to control bed bugs, it is important to preserve the few available tools.

No it is advisable to use insecticides recommended for bed bugs in the vegetative growth of soybeans or pests other than stink bugs in accordance with the action levels (Table 1). To use insecticides rationally will slow the evolution of resistance and preserve the few tools available to control this pest.

Differently of soybeans, in corn cultivation the green-bellied stink bug is considered a key pest at the beginning of the development of the culture, with significant losses in the implementation of the crop, reducing the stand, damaging the vigor of the seedlings and causing tillering when the attack is severe. This insect uses the straw as a place of shelter and survival. Thus, the succession with soybeans favors development, by allowing a green bridge between these cultures for the supply of food throughout the year. Therefore, the recommended monitoring in corn cultivation, this occurs even before sowing, through inspection at the straw, continuing after plant germination (Table 1).

Despite the main form of control available for D. melacanthus be based on the application of insecticides, it is important to develop alternative methods of managing this pest to help reduce the impact of this pest insect in the agricultural scenario in a more sustainable context. This is even more important in a scenario in which high populations of the pest are arriving with greater intensity and earlier in soybean and corn crops. Fact that has taken farmers to increase the use of insecticides, often without obtaining results satisfactory.

Use of “wasps”

A control method of agricultural pests that has grown a lot around the world is the use of control augmentative biological. This management tactic consists of releasing an agent biological pest control in the environment, to combat these pests naturally. Among the natural enemies potentially useful in controlling stink bugs in soybean crops, the egg parasitoid telenomus podisi (Figure 2) shows great performance and efficiency in combating bed bug eggs. Recently, studies have shown that this parasitoid has a preference for parasitizing eggs D. melacanthus in relation to other bed bugs studied (Table 2), showing their great biological potential to be used in the sustainable management of this pest. The parasitoid, upon finding the eggs of the bed bug, oviposits inside these eggs, and after approximately 14 days, other adults of the parasitoid emerge that will continue the control providing a lasting effect, compared to conventional chemical control. Another advantage of using egg parasitoids in the Integrated Management of Pests (MIP) is the fact that control is exercised over the egg, before any damage occurs. This allows, if there is any failure, another measure management can be adopted without harming crop production.

A commercial use of this parasitoid still depends on registration with competent authorities, in addition to research that definitively establishes all recommendations for its use (technology package) such as the quantity required in each release, suitable and inexpensive release forms, among others. Although not yet commercially available, its natural occurrence in field needs to be preserved. Therefore, unnecessary applications should be avoided of insecticides, preventively before the occurrence of pests or when the pest is below the action level. Prioritize the use of the most selective products parasitoids and other biological control agents, which are those that cause less damage to the survival of these natural enemies (Table 3). The preservation of these beneficial insects (enemies natural) will help to reduce the bed bug pressure observed in recent years in the soy:corn production system.

How it is As can be seen in Table 3, the insecticides for bed bug control are not very selective when telenomus podisi. Therefore, a strategy to preserve these natural enemies is to apply insecticides when is strictly necessary, that is, when the action level is reached (Table 1). Furthermore, as the Bedbugs are bad fliers and usually begin colonization by borders. In a well-executed monitoring system, it is often possible check for the beginning of the infestation. In this case, the application of insecticides can be done only on the border or in restricted regions of the area, preserving the natural enemies in the center of the crop. This recommendation is easier to carry out in large areas, where the effect of the border is more easily noticed.

Soybean harvest and invasive management

The majority of Bedbugs feed on plants in the reproductive phase, as they are food suckers. seeds. Therefore, despite the occurrence of D. melacanthus in the initial phase of corn crops, preliminary results research indicates that this insect is unable to develop and reproduce by feeding solely on these seedlings. In this context, evaluating the food preference of D. melacanthus it was possible to verify that corn seedlings are not preferential hosts of the pest, being only used during the harvest autumn/winter (second harvest) possibly to guarantee the survival of the insect in the absence of hosts in the reproductive stage. Cultural remains (soy seeds fallen on the ground, dry pods, volunteer soybeans) in addition to presence of invasive plants (such as trapoeraba, among others) may have a important role for the development and reproduction of these bedbugs in this field scenario. This information is important in formulating some hypotheses for the management of this pest in corn that need to be confirmed in future experiments:

1) It is important to reduce losses in the soybean harvest, as grains fallen to the ground could favor the insect development in the second harvest (corn);

2) It is important to carry out adequate management of weeds, since trapoeraba is a host preference in relation to corn seedlings.

At the in order to control the population of bedbugs and invasive plants in the end of the soybean cycle, precisely at the moment when there is a marked growth in population of the green-bellied stink bug, many farmers have been desiccating soybeans for harvesting in mixtures with insecticides. However, the use of insecticides in Crop desiccation can lead to residue problems from the insecticide used in grains, as verified in preliminary experiments carried out at Embrapa Soy (Table 4). An alternative to avoiding the problem of stink bug management in late infestations in soybean can be its management in corn, with the use of seed treatment with appropriate insecticides, foliar applications if necessary and a greater distance between the soybean harvest and the establishment of the corn crop, when the sowing window of the second harvest allows. Furthermore, it is important to highlight that in areas with good control of invasive plants, the stink bug population was reduced thus such as when insecticides were applied during desiccation, indicating the importance of good management of these stink bug host weeds.

Article published in issue 218 of Cultivar Grandes Culturas, July 2017.