​Advanced management

The presence of high populations of false meads has been a cause for concern in many cultivated areas in Brazil. The diversity of species, the geographic range of large crops, the long and hot summer seasons, the scheduled and indiscriminate applications, the growth of crops called “second harvest" or off-season in Brazil and also the difficulties inherent in the study and control of this group of pests have been the main reasons for population explosions of this increasingly frequent pest in agricultural crops in the country.

These false caterpillars are well known to Brazilian producers, because, despite having been characterized in the past as secondary pests, the presence of these species of caterpillars has become increasingly constant in the country's crops, mainly soybeans and cotton. And, in recent years, they began to worry Brazilian producers, as they changed their “status” from a secondary pest to a key pest of crops such as soybeans and one of the causes is certainly the abundance of food throughout the year.

The increase in this pest may also be linked, as many claim, to the use of fungicides in soybean crops, as in addition to controlling fungi that cause diseases in plants, these products may be eliminating entomopathogenic fungi, which play an important role in biological control. natural occurrence of many caterpillars, since the discovery of fungal diseases in insects has become a rarity in monitoring crops such as soybeans. A very common example is the fungus Nomuraea rilyei responsible for white disease in caterpillars. Its occurrence in soybean and cotton crops has become less and less frequent. Ultimately, whether it is the fungicide applications' fault or not, the problem with false measures has established itself quite drastically in crops and what is worse, producers only use chemicals to control this complex of "plusias", of which they are part The Chrysodeixis includens, Rachiplusia nu and Tricloplusia ni.

The most common species within this group of false measures is the C. includens, (Lepidoptera: Noctuidae) formerly called Pseudoplusia includens. The shapes Adults are moths with 35mm wingspan, and at rest these wings are arranged in the shape of a roof. The first pair of wings is brown in color with a coppery sheen, in addition to two distinct bright silvery spots in the central part of each wing. The second pair of wings is light brown in color and has dark edges. Furthermore, they have tufts of hair close to the head capsule.

The caterpillar is light green in color with a series of white, longitudinal lines distributed over the back, without lateral microspines on the integument and in the final stages of development the posterior region of the abdomen may appear bulky, with some specimens displaying black dots on the sides . The caterpillar can be called “medium-sized”, “inch-long” or “false-sized”. This name is due to the fact that it has only three pairs of abdominal legs, which forces it to walk a full inch throughout its development. .

In the initial phase it can be confused with the soybean caterpillar (Anticarsia gemmatalis) who also walks measuring inches, however, only in the first stages. This similarity in the initial phase of the two caterpillars has led many technicians to mistaken control recommendations, since the doses of insecticides used for soybean caterpillars are often half the doses recommended for soybean caterpillars.

The pupae are bright green and are generally located in casings built by the caterpillar itself with soybean leaves and silk threads that the insects themselves produce before pupating. The cycle from egg to adult can vary from 23 to 46 days on average (egg: from three to five days; caterpillars: from 13 to 23 days; pupa: from 7 to 15 days and longevity of adults: 15 days), and may present up to three generations per harvest and each female can lay up to 600 eggs, normally isolated and on the back of the leaflets.

Caterpillars generally go through six instars and the avidity for leaves increases as they develop, therefore, caterpillars in the first stages cause, with their attack, small semi-transparent spots, a consequence of the elimination of the leaf parenchyma, being observed, mainly in the middle third. bottom of the plants. As the caterpillars become larger, they begin to devour the tissue of the leaves, leaving only the veins behind, providing a lacy appearance that is very characteristic of the pest's attack. In addition to the leaflets, it can attack flowers and pods, an increasingly common behavior in soybean crops.

In Brazil, C. includens It can be found from North to South of the country, however, its occurrence has become common and increasing in crops where soybeans are grown, such as, for example, the Central-West, showing great adaptability even in regions with high temperatures. The fact is that according to recent studies, the change in the distribution of many species, including some insects, was induced by a modest increase in temperature of less than 1°C and this is certainly a warning about the dramatic effects of “global warming " continued over the next few centuries.

False medleys have a wide list of host plants, as around 70 wild and cultivated plants are recorded, with the capacity to maintain populations of C. includens, and in addition to soybeans and cotton, the pest's hosts are beans, cabbage, okra, sweet potatoes, tobacco, sunflower, lettuce, cauliflower, sesame and in recent years, mainly in state of Goiás, its presence in tomato crops has been increasing.

It is known that, among the insect pests present in soybean crops, defoliating caterpillars play a key role, as most of the problems faced by producers are caused precisely by these pests and false leafworms are currently the major villains. And one of the factors for this increase in the population of false pests is the inappropriate or prolonged use of non-selective and broad-spectrum agrochemicals, which eliminate not only the pest, but also natural enemies. Therefore, integrated management can be a path to balance between species that cause damage and their natural enemies.

When it comes to Integrated Pest Management (IPM), its implementation requires basic information about the biology, physiology and ecology of the pest in question and its natural enemies. Furthermore, knowledge of the phenology of the crop in the region, the climatic conditions, the population levels of the pest that the crop or cultivar can tolerate, without a drop in productivity, are essential to obtain positive results in the integrated management of these caterpillars.

It is understood that, in the vast majority of Brazilian production systems, crop succession is a tradition and, therefore, it is unlikely that producers will stop planting as long as the possibility of producing exists. However, staggered and/or successive cultivation, without a rest period for the area, allows an increase in the quantity of these phytophages, making crops great hosts of pests, including defoliators such as false leafworms. Therefore, if producers at least adopted the destruction of tigueras, ratoons and host weeds as a preventive measure, they would already make it difficult for these species to perpetuate themselves in the field. Furthermore, good agricultural practices such as, for example, adequate soil preparation, balanced fertilization, use of cultivars adapted to the region, combined with favorable climatic conditions, can help in the recovery of the leaf area after an attack by defoliators.

The first step towards establishing the management of this plusia complex in soybean crops is monitoring and, in this case, it is possible to adopt two fronts of observation. The first would be the installation of traps with the pest pheromone, a technology that has been available for some time in Brazil, but little used by producers. Another is the cloth beating method, with weekly monitoring. In integrated management, sampling is essential for real knowledge of the pest population in the area and will determine the most appropriate time to adopt any control tactic.

Natural biological control must also be taken into consideration for this pest and, in this case, it is worth remembering that the use of selective insecticides and the maintenance of refuge areas can facilitate the survival of the numerous natural enemies present and active in soybean crops, such as, for example, predators (bedbugs, carabids, spiders, earwigs, ladybugs, among others), parasitoids (such as the species Copidosoma truncatellum, a common parasitoid in caterpillars, and the Trichogramma spp., egg parasitoids) and diseases (including fungi such as N. rileyi and the viruses responsible, by the way, for numerous epizootics in this year's soybean crops in Goiás).

Therefore, it is very important that producers know and recognize the role of these great allies of crops in the field, as their observation and quantification can determine a level of non-action, which means letting nature itself, through natural enemies, do its thing. role controlling pests, with little or almost no human intervention. Making this option seems somewhat questionable to many, but it is necessary to understand that under normal cultivation conditions, defoliation may often not represent significant losses in productivity and ends up benefiting the establishment of natural control agents always present in soybean crops. . Furthermore, it gives chances for the cultivar itself to express its full potential for recovery from attacks by defoliators such as leafminers. However, this is an issue that is still far from being accepted, especially in the current reality of soybean cultivation in Brazil.

As for chemical control, the first step to take is to avoid scheduling and the adoption of excessive or preventative applications, as this complex of plusias does not have a predetermined day or time to appear in crops and unnecessary or indiscriminate applications can worsen the situation of this condition. and other pests in cultivated areas.

Based on the experience of many, it is known that false leafworm infestations are more frequent in the reproductive phase of soybeans, making control difficult in many cases, as these caterpillars are not as exposed as soybean caterpillars (A. gemmatalis). However, this is not a rule and decision-making must be based solely on monitoring. And, contrary to what has been adopted in recent harvests, the chemical insecticide must be used with the aim of changing the defoliator population to acceptable levels, without any environmental impact and with an economic return adjusted to the investment.

Among the classes used to control false insects are diamides, growth regulators, phosphates, carbamates, biologicals and naturalyte. However, it is important to highlight that not only the molecule, but the dose, the control percentage, the residual, the selectivity to natural enemies and, finally, the climatic conditions must be taken into consideration when choosing and applying the product.

It is also worth highlighting that control cannot be directed only at the larval stage of the pest, as adults, pupae and eggs can be interesting targets when aiming for more efficient and long-lasting control and, for this, the adoption of attractive baits. in the control of adults or even releases of parasitoids from eggs can be very viable alternatives and need to be further explored by producers and technicians in the area.

Another strategy to be used in Integrated Pest Management (IPM) is the technology of genetically modified (transgenic) plants, which are tolerant to caterpillars due to the insertion of genes isolated from entomopathogenic bacteria. Bacillus thuringiensis (Bt). The inclusion of these genes Bt in plants it allows the production of proteins that have insecticidal action and thus begin to protect the plants against the attack of certain defoliating pests, including false leafworms. However, the adoption of this technology requires certain precautions, which include the establishment of refuge areas, which consist of the cultivation of conventional plants close to the areas bTS. The refuge produces susceptible individuals that can mate with the resistant individuals present in the culture Bt, thus increasing its efficiency and delaying the evolution of resistance in the technology's target pests.

Despite the economic and environmental advantages of IPM, the adoption of different tactics in an integrated manner, according to scholars, is slow and what is called IPM by many, in fact, is nothing more than “integrated insecticide management", or the so-called IPM of first tier, which consists of pest consultants monitoring crops to determine when to apply insecticides. The reasons for the lack of adoption of an advanced IPM, which takes into account not only the employment of different control tactics, but also the costs and benefits social, are known and include the lack of data on the ecology of pests and their natural enemies, the need for interdisciplinary research, the practicality that chemical control offers compared to other control tactics and, finally, the lack of suitable training for both farmers and technicians and consultants.

Finally, many need to understand that there are countless ways to manage insect pests in current agricultural crops, however, none of them, if used in isolation, will be able to remain efficient over time.

Differences between the most common defoliating species in soybean crops:

		Chrysodeixis includens	Rachiplusia nu	Anticarsia gemmatalis
Coloration and Morphology	caterpillars	Green with a series of longitudinal white lines, no microspines on the integument and the presence of two pairs of abdominal legs, in addition to an anal one that can reach up to 45mm in length in its last larval stage	Green with a series of longitudinal white lines, with microspines on the integument and the presence of two pairs of abdominal legs, in addition to an anal one that can reach up to 40mm in length in its last larval stage	Variable coloration from green, reddish-brown and even black, with five longitudinal white stripes on the back and the presence of four pairs of abdominal legs, in addition to one anal, reaching up to 30 mm in length in its last larval stage
	Butterflies	The first pair of wings is brown in color with a coppery sheen, in addition to two distinct bright silvery spots in the central part. The second pair of wings is light brown in color and has dark edges. At rest, the wings are arranged in the shape of a roof, with a wingspan of up to 35mm.	The predominant color is brown, the forewings have a small silver design similar to the letter “y” and the hindwings are dark yellow. At rest the wings are arranged in the shape of a roof, reaching a wingspan of up to 30mm.	Grayish-brown, with its general color varying between gray, brown, beige or light blue. At rest, the forewings cover the body, always having a transverse line joining the tips of the first pair of wings, reaching a wingspan of up to 35mm.
	Pupae	Pale yellow to light green and located in a cocoon constructed of leaves and silk threads	Dark brown to black, located in a cocoon constructed of leaves and silk threads	Dark brown located in a pupal chamber under dry leaves on the soil surface or up to 5cm deep
	Eggs	Approximately 0,5mm in diameter placed, generally on the back of the leaves and light cream in color and light brown near the hatch	Approximately 0,5mm in diameter placed, generally on the back of the leaves and yellowish-white in color	Approximately 0,6mm in diameter, generally located on the back of the leaves and are whitish to light green in color and reddish-brown close to the hatch.
Type of defoliation		Initially, they scrape the leaves and then start to devour them, but they do not consume the veins, leaving a lacy appearance, especially in the lower middle third of the plants. It can consume up to 200 cm² of leaf area during its development	Initially, they scrape the leaves and then start to devour them, but they do not consume the veins, leaving a lacy appearance, especially in the lower middle third of the plants. It can consume up to 200 cm² of leaf area during its development	Initially, they scrape the leaf and then begin to devour the leaf blade, mainly from the upper middle third of the plants. It can consume up to 150 cm² of leaf area during its development

Chrysodeixis includens

Rachiplusia nu

Anticarsia gemmatalis

Coloration and Morphology

caterpillars

Green with a series of longitudinal white lines, no microspines on the integument and the presence of two pairs of abdominal legs, in addition to an anal one that can reach up to 45mm in length in its last larval stage

Green with a series of longitudinal white lines, with microspines on the integument and the presence of two pairs of abdominal legs, in addition to an anal one that can reach up to 40mm in length in its last larval stage

Variable coloration from green, reddish-brown and even black, with five longitudinal white stripes on the back and the presence of four pairs of abdominal legs, in addition to one anal, reaching up to 30 mm in length in its last larval stage

Butterflies

The first pair of wings is brown in color with a coppery sheen, in addition to two distinct bright silvery spots in the central part. The second pair of wings is light brown in color and has dark edges. At rest, the wings are arranged in the shape of a roof, with a wingspan of up to 35mm.

The predominant color is brown, the forewings have a small silver design similar to the letter “y” and the hindwings are dark yellow. At rest the wings are arranged in the shape of a roof, reaching a wingspan of up to 30mm.

Grayish-brown, with its general color varying between gray, brown, beige or light blue. At rest, the forewings cover the body, always having a transverse line joining the tips of the first pair of wings, reaching a wingspan of up to 35mm.

Pupae

Pale yellow to light green and located in a cocoon constructed of leaves and silk threads

Dark brown to black, located in a cocoon constructed of leaves and silk threads

Dark brown located in a pupal chamber under dry leaves on the soil surface or up to 5cm deep

Eggs

Approximately 0,5mm in diameter placed, generally on the back of the leaves and light cream in color and light brown near the hatch

Approximately 0,5mm in diameter placed, generally on the back of the leaves and yellowish-white in color

Approximately 0,6mm in diameter, generally located on the back of the leaves and are whitish to light green in color and reddish-brown close to the hatch.

Type of defoliation

Initially, they scrape the leaves and then start to devour them, but they do not consume the veins, leaving a lacy appearance, especially in the lower middle third of the plants. It can consume up to 200 cm² of leaf area during its development

Initially, they scrape the leaves and then start to devour them, but they do not consume the veins, leaving a lacy appearance, especially in the lower middle third of the plants. It can consume up to 200 cm² of leaf area during its development

Initially, they scrape the leaf and then begin to devour the leaf blade, mainly from the upper middle third of the plants. It can consume up to 150 cm² of leaf area during its development

Click here to read the article in issue 178 of Cultivar Grandes Culturas.