Bugs: the biggest cost in pest control in Brazil

Phytophagous bugs are currently the highest single cost among pests in soybean crop management and also in production systems involving other crops such as corn and cotton.

One of the biggest complaints from several producers is the early arrival, the “population explosions – rapid population growth”, the understanding of population dynamics and actions for its management.

This aspect has led technicians to reflect on analyses for improvements, given the great losses caused by this pest or even the increase in production costs, due to its control.

Year after year, pests, due to climate change and changes in the production system, lead to great losses for the producer. The agroecosystem used in the more than 43,4 million hectares of soybeans in Brazil (Conab, 2023), has several characteristics that favor the multiplication of pests, as a production system prevails in which soybeans are the main crop to be established, in the vast majority of areas, and can be rotated or not, with a crop established after harvest in succession or even left “fallow”, providing food for pests.

In this way, there is a host throughout the year and, combined with other factors such as favorable climatic conditions, high temperatures and mild winters, it becomes ideal for the multiplication of insects.

In the 2022/2023 harvest in Brazil, there was a delay in sowing, reaching 25 days in certain regions. The climate factor greatly influences the pest cycle, coinciding in most cases with the crop (main target - food). When the sowing process starts too early, it leads to long sowing “windows”, favoring multiplication, very common in regions with irrigation, or even due to rains that arrive before other areas.

The first areas sown in recent years have seen a great attack by various pests. This occurrence is due to it being one of the only places for them to find shelter – food, or even the exit of processes such as diapause and migration.

Some pests such as cowpeas, mealybugs (Myochrous sp.) and even caterpillars have led producers to make some interventions, which often using products with a broad spectrum of pests, can lead to certain population imbalances.

Another factor that correlates with the increase in these pests is the increase in the frequency of tigueras plants (plants left over from previous crops – corn being the most frequent example). The prominence of these plants in the system, and their tolerance to glyphosate, often leads to the search for other alternatives, which are sometimes more expensive and difficult to work with.

Some studies observed that corn cobs that fell to the ground generated 6 corn flows (Adegas et al., 2015), which can generate a greater number of applications for the producer in soybean crops, especially in areas with gaps in the stand.

The adaptation of bedbugs to the production system is also a factor in increasing problems. This has been occurring for several years, with the off-season being an important time to understand their dynamics (Rattes, 2004). In general, over the years, bedbugs have adapted to various weeds, some of which are currently more prevalent due to the selection of herbicides used. Among the most prominent weeds in the central region of Brazil is trapoeraba (Commelina benghalensis), bittergrass (Digitaria insularis), horseweed (conyza bonariensis), button broom (Spermecocea verticillata) and finally the chicken foot grass (Eleusine indica) resistant to both graminicides and glyphosate.

Among the species, it is worth highlighting Dichelops (Diceraeus) melacanthus in weeds of C. benghalensis e E. indica (Tomquelski et al., 2015 and Castro et al., 2020). The corn areas in the succession showed damage greater than 20% when the pest and the weed were present.

Over the years, changes have been observed in relation to species. The brown stink bug, Euschistus heros (Heteroptera: Pentatomidae), is widely distributed in crops in the Cerrado region. In the Chapadões region, they represented more than 87% of the species present in samples from soybean crops in the 2021/2022 harvest.

Other species of bugs are associated with the agroecosystem such as the green-bellied bug (Dichelops (Diceraeus) melacanthus e D. furcatus), the edessa bedbug (Meditating Edessa) and the small green stink bug (Piezodorus guildinii), occurring in certain areas with great losses.

In general, these pests have a cycle of around 20 to 50 days, and may go through periods of diapause when there is no food. One of the highlights is D. melacanthus which has a shorter cycle and a greater reproductive capacity, with the female being able to lay more than 80 eggs.

Analyzing the cycle of bedbugs and soybean crops, it can be observed that up to 4 generations can occur in the crop, depending on the cultivar cycle and other factors. The amount generated at the end of the crop can be very difficult to manage.

At the end of the soybean crop cycle or after harvesting, bedbugs migrate to adjacent crops or remain in the area due to crop residues that fall from machines during the harvesting process, and then attack subsequent crops, leading to major losses.

Soybean grains often end up generating plants in subsequent crops (in this case, second-crop corn). These plants often allow the pest to develop and generate more generations, preventing it from leaving the area.

Corn has migrated from the summer harvest to the 2nd harvest = “safrinha” (Conab, 2021). In this system (soybean – corn), bedbugs have generated average losses of around 20% in large corn-producing regions. It is worth noting that in certain plots the losses reached 100%, requiring reseeding.

Another factor is added to the analysis of the scenarios - the area of ​​transgenic plants in Brazil increases year after year. Currently, more than 90% of the soybean area is used with Bt technology (resistance to certain defoliating caterpillars). The use of certain insecticides in the past led to the break in generations, mainly in the vegetative stage of the crop, causing it to arrive later (already in the reproductive stage).

This is one of the recommended tools within Integrated Pest Management - IPM, however, for convenience, some producers adopt it without criteria, without analyzing population dynamics.

Pests such as bedbugs are unevenly distributed across plots, requiring greater accuracy from the technician involved in sampling. Studies carried out by Tomquelski et al. (2018) show the problem of bedbugs at the beginning of the infestation, occurring in “spots” that infest more than 50% of the plots within a week.

The producer often has the impression that the pest is not present, which commonly occurs due to monitoring failures (“false negative”), however the population increases exponentially in one week, making management difficult.

In sampling, it is important to highlight that in recent years, advances have been developed, including the use of pheromones. These tools lead to greater accuracy, especially in the arrival of the pest, which normally occurs during the vegetative period.

This tool has been used for some years (Pires et al., 2006; Silva et al., 2014), although it is not yet commercial, but it is observed that the pest in the vegetative period from the arrival of females – fertile – without parasitism, can have a large population growth, generating a high number of individuals to be controlled in the reproductive period, the harmful phase of the pest to the crop.

When sampling, care should be taken with nearby refuges, or even older plots, as this could be the beginning of the infestation. In general, bedbugs do not fly over great distances like other pests (lepidopterans fly over more than 500 meters), and borders are important places for observation.

Damage to soybean crops occurs during the reproductive phase, starting with the formation of pods, also commonly called the formation of “canivetinhos”, leading to their fall and subsequent malformation of the grains. During this phase, bugs concentrate in these parts, both as nymphs and adults. Interestingly, in some cases, only 10% of the total population present on the plant can be found on the leaves of the plants. Bugs suck the sap from the branches, stems and pods.

When sucking, they can inject toxins that cause “leaf retention”, that is, the leaves do not fall normally and make mechanical harvesting difficult.

In corn, the growth point of the plants is the target in the initial phase, with bugs of the genus Diceraeus sp. causing the greatest damage. Their stylet can reach the meristem of the plants, causing deformation of the plants, compromising their development and consequently the occurrence of “dominated” plants that do not produce ears.

Some studies show that coexisting with levels above 2 bugs per meter of row in soybeans can lead to the occurrence of leaf retention, also called “crazy soybean 1” (Eduardo et al., 2018). This fact is very common to observe in the field, often due to the interval between applications, which is often scheduled with the fungicide (around 15 to 20 days).

Currently, the quality of grains has led to greater care, being a point of attention when the producer needs to store the grains for longer periods. Bedbugs, due to their bites on the grains, lead to the entry of fungi (Nematospora coryli) there may be an increase in “burnt” grains that are then discounted at the time of shipment, or even discounted upon arrival from the industry

The characteristics of these attacked grains are often smaller, wrinkled, shriveled and darker. During the storage process, chopped grains lead to loss of mass over time, and in this case, trading companies have increased the rigor in classification and entry of the product into the warehouse.

Monitoring work carried out by Tomquelski et al. (2020) observed that in the Chapadões region there were variations of 3 to 32% of grains bitten by bugs in soybean loads, which is a point of attention for the work of classifiers when loading the loads.

Producers who have silos on their farms should be monitoring this factor, as some samples with more than 30% of attacked grains caused losses of around 2% when the mass was stored for more than 3 months (Tomquelski et al., 2016).

For the management of phytophagous bugs, attention to understanding the population dynamics and the use of integrated strategies are fundamental factors. Management is largely carried out using chemical control, an efficient and fast technique that can be used in large areas. However, it is important to highlight that there are few chemical groups available, and the tools may not work as expected.

In the initial phase of soybean cultivation, the chemical group of organophosphates is often used, with acephate being the largest representative. In recent years, this insecticide has provided rotation between ready-made mixtures of neonicotinoids associated with pyrethroids. The results of research have shown consistent results of acephate on adults of Euschistus heros, being an important tool in breaking the pest cycle during the vegetative stage, if necessary, with the crop “open”. In this phase before the crop closes, the insecticides bifenthrin + zetacypermethrin, profenofos + cypermethrin and fenitrothion + esfenvarelate are still available, with results of around 80% control.

This crop closure - vegetative phase of soybeans - has seen major changes over the last decade. The introduction of new cultivars with indeterminate growth habits, flowering in 28-35 days, has led to earlier pod formation, and consequently the lower third "lower" has gained greater importance in productivity.

With the closure, the producer must pay attention to the control of nymphs, often due to the “leftovers” of the pest in the system – control. The work of Tessmer et al 2022 reports an important fact that is often not carried out, the counting of nymphs of the 2nd stage of these pests. These are insects that are often beginning the process of dispersion in the crop (leaving the agglomerated form – 1st instar) and are no longer as affected by the action of natural enemies and climate, causing significant damage to the crop (grains – seeds).

In this case, ready-made mixtures of pyrethroids and the large group of neonicotinoids have shown good control, as they provide greater control in days. Currently, thiamethoxam + lambdacyhalothrin, imidacloprid + bifenthrin, imidacloprid + betacyfluthrin, acetamiprid + bifenthrin stand out, in addition to the new insecticides dinotefuran + lambdacyhalothrin, sulfoxaflor + lambdacyhalothrin and, lastly, lambdacyhalothrin + acetamiprid. Other insecticides that stand out for rotation are mixtures of carbosulfan + bifenthrin and ethiprole.

Under different conditions, the producer awaits new molecules, new mechanisms of action, as well as new solutions.

In the last harvests, a large number of bugs of the species were observed D. melacanthus generally in the Brazilian Cerrado region. This species can use the cotyledons for its food in soybean crops and normally does not climb very high into the plant canopy, requiring greater care with the application technology, or even the management strategy. Many areas have required applications at the end of the crop – close to defoliation – desiccation, in order to reduce populations for the subsequent crop (2nd corn harvest). Despite the low efficiency of the method in this species, the results are still satisfactory for reducing the number of plants attacked in the 2nd corn harvest.

In general, combinations of adverse factors have led to errors in the positioning of tools. It is clear that producers often tend to wait for the fungicide to be applied, which may be too late, since the pest can reproduce depending on alternative hosts, or even “early” application or “scheduled” applications without the need for it. The application interval for most insecticides on the market when we have the presence, excess application or re-infestation is 7 to a maximum of 10 days between applications (graph).

In the Chapadões region, monitoring carried out in recent years has shown a drop in parasitism, with values ​​in the last harvests being around 20% of the bedbug population.

Biological control with parasitoids Trisolcus basalis e telenomus podisi tends to increase in view of the increase in biological companies, in addition to release strategies, with the use of Drones - UAVs, which makes the work easier for the producer. New formulations of fungi with Metarhikum anisopliae has added to the management results.

The climate can undoubtedly affect the occurrence of pests as well as the efficiency of methods. Frequent rains and high precipitation lead to a decrease in the effectiveness of most available insecticides.

Some regions still suffer from rain during harvesting and operations (machine yards), where the end of the soybean crop presents high populations of bugs, which has led to great losses in quality. It is very important to analyze these pest indices in the production system (after sowing the subsequent crop) and in addition to grain quality, they become fundamental for the success of management. If necessary, the producer should reduce the population while still in the soybean crop.

Only the recovery of Integrated Pest Management, with better knowledge of the pest – biology, good sampling and attention to infestation levels, tends to support control strategies. Currently, several digital tools are available to improve sampling, such as georeferencing of points and construction of area history.

There are several insecticides on the market, the producer must pay attention to the positioning of the tools – integration of methods, and certainly, the owner's eye (sampling) will make the difference, improving their final profitability.

For now, the producer is winning the battle against bedbugs, but the war is not over yet.

By Germison Tomquelski e Paulo Chagas, Agro Challenges

Text from the technical notebook that circulated in issue 287 of the Cultivar Grandes Culturas Magazine