Integrated Pest Management (IPM) was developed with a broad vision, considering the complex of phytophagous insects that could reduce crop productivity and, consequently, the profitability of those who produce. Obviously, the sustainability of the production system is also embedded in the concept, with regard to high quality, not only of the product, but also of the environment where it was produced. Unfortunately, the faithful use of MIP has been reduced over time. Due to a sole decision by the producer or even influenced by others, it is common to consider only one or a few species as important pests (keys), which over the years receive a greater number of interventions for control, regardless of their population level, and in general with the use of sprays with macro or micro-organisms. In large individual areas, it is common to purchase chemical products, considering a high degree of “certainty” that a certain pest will be present in the crop and will require control measures. If the pest does not require control, the product will be stored for the next planting or may be used to control another species. Therefore, it is possible to apply a product that is not appropriate, or, worse, apply it without it being registered for the pest of the moment, affecting the corn crop.
The fall armyworm, Spodoptera frugiperda, was identified in 1797, and until recently was confined to the Americas. It is currently found in several countries in Africa and Asia. It is the main pest of corn in Brazil, and despite the existence of several commercial products and genetically modified plant seeds (corn Bt), continues to reduce crop productivity, increasing production costs and reducing farmer profitability. This fact suggests, and has already been confirmed by scientific studies, that this pest is capable of becoming resistant to the technologies used, whether based on chemicals or even corn plants. Bt, or that such technologies are not being used properly. Therefore, it is essential to implement a correct pest management program that will provide gains for both the farmer and the consumer. Furthermore, logically, the environment itself will benefit, since MIP in principle also aims to ensure the sustainability of the production chain. The expected success in pest management may not occur without prior planning and considering several technical criteria, including possible undesirable side effects of the chosen control method, mainly in relation to non-target organisms, especially beneficial insect fauna, including natural biological control agents.
The presence of the insect in the crop can be noticed at practically all stages of the plant's development. However, injuries in the early stages of development are those that quickly attract the farmer's attention, but they also mean that the larva is already present, making it necessary to quantify this presence and compare it with its level of economic damage to then make a decision about the need to carry out control.
Initially, two basic points must be considered when implementing a waste management program. S. frugiperda. The first of them is about the average potential reduction in grain production of a plant after being damaged by a healthy larva, currently considered to be around 30%. The second point is in relation to the level of economic damage (NDE), that is, the population level of the pest present in the production area which, if not efficiently controlled, would cause an economic loss at least equal to the cost of its control. This cost must include the cost of purchasing the product and the amount to be paid for the services used before, during and after application. Obviously, the economic loss is a function of the drop in expected productivity and the price of corn. Considering that there is similarity in the total cost for pest control, regardless of different technological levels used in production, it is easy to understand that the level of economic damage will vary. Therefore, an individual production unit must have its own NDE. Knowing the pest's potential to reduce plant production, the economic value of production and the total cost involved in control, the NDE (calculated value) can then be determined.
Knowing the NDE for a given agricultural holding and in a specific year, the next step is to compare the value calculated for the NDE with the real incidence of the pest in the area. If the incidence of the pest is at a level close to or higher than the value indicated by the NDE, control must be carried out, as there is a high probability of economic losses if the pest is not controlled. This statement, however, is not so simplistic; is correct in the sense of making the decision about the need for control, but applying the product is not enough to obtain efficiency.
The farmer must be aware of variables that can significantly affect application performance. One of them is the developmental stage of the pest, as larvae of different ages require dose adjustments of the product used, whether chemical or biological. And this difference in the stage of development of the larvae is a function of the entry flow of moths into the crop and the time in which the survey was carried out to determine the actual infestation of the pest. Therefore, the survey, often carried out based only on the symptom of apparent damage, may not adequately estimate the presence of the larva and/or its stage of development.
Checking the presence of larvae, computing its percentage distribution by age group and making, if necessary, appropriate adjustments to the dose of the product to be applied are an improved method of monitoring and making decisions about the need for control. However, it is an expensive method and requires special care to avoid damaging the plant. In general, between 1% and 2% of the plants in the cultivated area must be sampled in the two systems mentioned, and sample points containing between 50 plants and 100 plants can be considered. The greater the number of points, selected at random, the better the quality of the information.
Another alternative for monitoring S. frugiperda in corn is through the use of a trap containing a removable sticky floor and the pest's synthetic sexual pheromone (http://agrofit.agricultura.gov.br/agrofit_cons/principal_agrofit_cons). The objective of this method is to identify the presence of the moth in the target area throughout the crop cycle, and should be used shortly before or on the day of corn planting. Decision-making for pest control is based on the average accumulated capture of three moths per trap (http://dx.doi.org/10.18512/1980-6477/rbms.v9n2p107-122), considering that a trap is enough to monitor five hectares in homogeneous areas. In other words, three or more moths captured mean a high probability of having a population of larvae with the potential to reduce corn productivity, whose economic value is at least equal to the cost of control, within an expected productivity level of 150 bags of corn. corn per hectare. Using this criterion, and if spraying is the chosen strategy, it should be carried out ten days after the accumulated capture of three moths. The larvae will be around seven days old and very susceptible to the product to be applied, whether chemical or microbiological.
Continued monitoring with traps will indicate fluctuations in moth flow throughout the corn cycle (Figures 1 and 2). Figures 1 and 2 show moth capture data for an entire year, in Sete Lagoas, Minas Gerais. In agricultural environments with fluctuating moths and a low incidence of natural control agents, the potential for reducing corn productivity will certainly be high, and this situation is likely to occur in several agricultural environments in Brazil, involving corn cultivation. .
It is essential, therefore, to be successful in controlling S. frugiperda in corn, that the producer, individually or through cooperatives or rural unions, is aware of the fluctuation of the pest, even in areas without corn planting, considering that the Larvae can use more than 60 plant families as a food source. This monitoring is essential for the production of scaled corn, as is the case with corn for fresh sale or that produced for the agroindustry.
Observing the fluctuation of the pest over time, a great doubt arises about the necessary number of applications for control during the corn crop cycle, especially considering the short residual period obtained with products via spraying. This is without considering the great population pressure on Bt corn plants, with several examples of loss of efficiency in controlling the pest. Therefore, it is necessary to use sustainable alternatives for pest management, which alone or integrated with others of the same principle provide lasting control of the target pest and maintain the others at an acceptable level. An alternative is the priority inclusion of biological control, especially with the use and management of macrobiological organisms such as beneficial insects (parasitoids and predators).
Although little used in the past, demand for the use of biological control of insect pests is currently growing. And the incidence of natural control agents for larvae of S. frugiperda in commercial corn areas indicates how useful the method can be in the integrated management of the pest. The use of beneficial insects can occur through the acquisition and use of biofactory products (applied biological control) and/or through the conservation of beneficial insects already present in the agricultural environment. In this case, exercising natural control over one’s own S. frugiperda and other phytophagous species.
Monitoring carried out in 97 municipalities in Minas Gerais, over a period of eight years, through collections of larvae of S. frugiperda in corn plants and on rural properties, it indicated the presence of natural enemies in 99%. Figure 3 shows the municipalities with parasitism rates between 40,4% and 71,4%. Greater or lesser incidence of populations of pest species is a function of, among other factors, the biodiversity of beneficial species.
Among all parasitoids, Chelonus insularis, Campoletis flavicincta e Eiphosoma laphygmae, together, represented 74,1% of the species obtained (Figure 4). The species C. insularis lays its eggs inside the eggs of S. frugiperda, however, it allows the pest larvae to hatch; the other two species are exclusive to small larvae, and, for all, the parasitized larva reduces food intake by more than 90% before being killed. A single female C. flavicincta can parasitize and kill up to 200 small larvae of S. frugiperda (Figure 5). The presence of these parasitoids and other species of beneficial predatory insects, such as earwigs, Doru luteipes, species of bedbugs, such as Zelus and Podisus, ladybugs and litterbugs, can certainly be a great ally for the farmer in controlling the pest complex. of corn, especially when the farmer starts using practices that do not reduce the survival and population development of these beneficial insects.
the species Trichogramma pretiosum, a tiny insect, is increasingly used in Brazil, on corn and other crops, due to its mode of action and release, its efficiency and mobility and its competitive cost. The use of this type of control S. frugiperda it can be thought of both as an alternative to the use of a chemical product without loss of efficiency and as a strategy to avoid the very early elimination of different species of beneficial organisms of great importance in maintaining bioecological balance, acting to reduce other species of phytophagous insects. Additionally, the fact that there are no pests resistant to biological control with the wasp must be considered. Trichogramma and being a technology that does not generate environmental liabilities.
the species T. pretiosum is an egg-exclusive parasitoid and passes all stages of development, with the exception of the adult stage, inside the eggs of S. frugiperda, and the fact that it is exclusive to eggs prevents the hatching of larvae and consequently prevents any foliar damage. The insect can be released in the field in several ways, from manual release to release via drone, in this case for large areas. Unlike control carried out via spraying, which needs to reach the larva or the location where it is found on the plant and on all plants, the wasp Trichogramma, due to its mobility, it can be released in groups, in some parts of the area planted with corn. On average, females are released at a density of 60 per hectare, distributed in 20 equidistant points.
Trichogramma can be released in the pupal stage within an egg of an alternative host, usually a meal moth egg, Anagasta kuehniella, very close to the emergence of the adult or in the adult phase. The newly emerged female immediately begins the search for the egg. S. frugiperda to lay its own egg and thus perpetuate the species. An indication of parasitism in the pest eggs is that they become blackish about four days after receiving the pest egg. Trichogramma. A generation of T. pretiosum is completed in about ten days, contrasting with the cycle between 30 days and 40 days of S. frugiperda.
The efficiency of Trichogramma depends on the synchronization between release in the field and the presence of pest eggs. For this to occur, monitoring must be aimed at identifying the posture or, better yet, by capturing the moth in the pheromone trap. Decision-making for pest control is based on the average accumulated capture of three moths per trap, with the release of the parasitoid shortly thereafter. The insects are purchased from commercial biofactories, which are generally associated with a company providing the release service, usually via drone.
In places where there is no knowledge about the population of natural biological control agents or when it is small or non-existent, the release of Trichogramma can be carried out in three stages, each time releasing a third of the global density.
If the producer chooses to use a control measure via spraying, the product, preferably microbial or chemical, must be chosen based on positive characteristics, in addition to its efficiency against the pest and its cost. Without prior knowledge, choosing is an arduous task, considering there are over 200 brands of commercial products available (http://agrofit.agricultura.gov.br/agrofit_cons/!ap_praga_detalhe_cons?p_id_cultura_praga=3531). The inefficiency of the application can be attributed to the incorrect choice of the type of spray nozzle, the volume of water, the application pressure, the stage of plant development, rainfall immediately after application, etc. Larvae that receive insufficient doses to kill them gradually acquire resistance to the applied product, and thus, over time, this degree of resistance increases in the pest population, demanding new applications, increasing production costs and causing biological imbalance. .
Ivan Cruz, Embrapa Corn and Sorgo
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