Although intensive agriculture for the production of commodities is less than 100 years old, several strategies were used during this period to control agricultural pests. All of them, without exception, used the most modern technology at the time, such as DDT and transgenic plants. In fact, they promised to “free” farmers from pests quickly, with maximum efficiency and low cost.
The 21st century scenario shows that the use of these and other strategies needs to be reviewed and optimized. Despite their numerous benefits, there are increasing and constant reports of pest resistance to pesticides and Bt plants, which often results in an increase in the dose and number of applications. Society's growing concern about residues in the environment and in food, and their impacts on ecosystem services (pollinators and natural enemies) has increased the debate on more sustainable agricultural management.
Biological pest control agents, whether macro (parasitoids and predators) or microorganisms (fungi, viruses, bacteria and nematodes) are important pillars of this sustainability. Although the first successful case of biological control in the world dates back to 1888, with the import of a ladybug by the USA for pest control in citrus, in Brazil, only in the last decade have successful cases, such as the BUG starter and the use of Bt bioinsecticides against Helicoverpa armigera, demonstrated that trading in these control agents can be a sustainable and profitable business activity.
Since then, the number of companies producing biological control agents has been growing exponentially in Brazil. Much of this increase is due to the low cost of development and the much slower evolution of resistance compared to conventional insecticides and Bt plants. However, several challenges remain for their success to be achieved and consolidated, including: improvements in formulations, assessment of compatibility with pesticides and, especially, technology and application.
Historically, in Brazil, knowledge of the biological target, that is, the insect or mite pest to be controlled, has been disregarded in favor of structured marketing only for the product being sold. Insects have great genetic variability and adaptive capacity, the result of 300 million years of evolution, which resulted in their survival and conduction to the status of the largest known group of species on the planet.
That said, this article describes the importance of knowing the target of the application in biological, ecological and behavioral terms, so that this information can be incorporated into the application technology to maximize the control potential of bioinsecticides. This strategy is essential for these products to be considered one of the pillars of sustainable pest management.
The predominance of the use of broad-spectrum insecticides and transgenic plants in pest control has led to the simplification of agricultural activities and, consequently, the premises of integrated pest management, especially pest identification and monitoring, have been relegated to a secondary role, mainly due to their cost and operational difficulties.
However, this “comfortable” situation did not last due to the complexity and instability of the agroecosystem. Outbreaks of helicoverpa spp. were reported in the Brazilian Cerrado in 2012 and subsequently in other regions of Brazil, with impressive losses of around US$ 2 billion. These damages were initially attributed to helicoverpa zea, a very common pest in corn crops, and farmers soon began using insecticides registered for this pest. However, the lack of success in adopting these products became evident when new outbreaks were reported in several regions of Brazil in the second half of 2013, although insecticide sales increased by approximately 40% between January and July 2013.
However, in early 2013, researchers from Embrapa collected this insect in several locations in Brazil and identified it as Helicoverpa armigera, a species that had not yet been reported in Brazil. Subsequent studies demonstrated that this insect entered Brazil between 2006 and 2008. Correct identification of the species was essential to enable its control, as it implied a review of the management methods used until then. This pest is now under control throughout Brazil.
When positioning the biological product, information about the insect can be used, such as the behavior of the pest species; migration, or even movement within the plant. In a study carried out by entomologists from the Federal University of Santa Maria, it was demonstrated that the behavior of lepidopteran pests of soybeans varies during the night and day. The false looper caterpillar (Chrysodeixis includens) prefers to remain in the lower part of the plant during the day (warmer periods) and during the night, some of the caterpillars from the middle third migrate to the upper part of the plant, due to the milder temperatures. The soybean caterpillar (Anticarsia gemmatalis), in turn, prefers the middle part of the plant, with most specimens located in the upper part during the day. However, the species that presented the most striking differences was the Spodoptera eridania, with most caterpillars preferring the lower part of the plant during the day, while at night, most of them are located in the upper third of the plant.
Caterpillars on the upper part of the plant are an easier target to hit than caterpillars on the lower parts of the plant. The movement of the caterpillars, in this case, C. includens e S. eridania, throughout the day, can be taken into account when deciding the best time to apply. Furthermore, spraying bioinsecticides at night can improve their efficiency, due to milder temperatures and humidity compared to daytime conditions.
Bioinsecticides are more efficient against the first larval instars (1st and 2nd) of lepidopteran pests, while from the third instar onwards the efficiency is reduced by more than 50%. In a study carried out with H. armigera, at the Laboratory of Microbial Control of Arthropods in Prague at FCAV/Unesp, it was demonstrated that fifth instar caterpillars (LC50 1.420 ng Cry1Ac/cm2 of artificial diet) are 45 times less susceptible than first instar caterpillars (LC50 31 ng Cry1Ac/cm2 of artificial diet). Later, another study demonstrated that, for C. includens, this difference was even greater: about 400 times.
In practical terms, a large caterpillar (from the third instar onwards) has a greater chance of recovering from infection by an entomopathogen such as Bacillus thuringiensis (Bt), for example. To do this, your immune system starts a process to repair your midgut (Bt's target), discarding dead cells and producing new ones. Ingesting a greater quantity of food is essential for this recovery, which can translate into greater foliar consumption under field conditions.
The three aspects mentioned above: taxonomy, pest behavior and age composition, depend directly on monitoring to achieve their objectives. Although costly and difficult to implement, there are examples where it can be used with economic returns for the producer.
The thesis defended in 2013 by Professor Valmir Aita, from UFSM, concluded that monitoring with a 50 × 50 m sampling grid for defoliating caterpillars can be financially viable. In fact, this sampling demonstrated that the highest population of caterpillars was localized, making it unnecessary to apply insecticides to the entire area. Thus, the higher cost of sampling using a grid was offset by the savings in insecticide application of 57%.
It should be noted that the use of unmanned aerial vehicles and smart traps in crop monitoring will be important tools that will make this activity possible in very large or difficult-to-access fields. The development of these technologies in the coming years will provide more detailed monitoring in terms of specific pest populations and behavior.
Scientists have accumulated valuable information for managing agricultural pests, but most of the time, this information does not reach producers. It is necessary to strengthen relations between the different sectors of agricultural activity so that the exchange of information makes it possible to optimize the use of pest control tactics. It should be noted that this is not an exclusively Brazilian need, as demonstrated by the article published in the journal Biological Conservation (https://doi.org/10.1016/j.biocon.2021.109065). In this study, a group of researchers interviewed around 300 farmers and scientists in Germany and Austria. The authors emphasized the urgent need to strengthen the dialogue between scientists, farmers and companies regarding research, field practices and agricultural policy.
By Ricardo Antonio Polanczyk, Unesp
Article published in issue 290 of Cultivar Grandes Culturas Magazine
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By Weslley Buratto, Antonio Tassio Santana Ormond, Alicia Cristino Arenhart, Gessiel Mendonça Leles and Marcos Ferreira do Prado, from Unemat, and Willian Buratto, from UFMT
