The attack of insects, from planting to close to harvest, is a limiting factor for crop productivity, regardless of the production system used. Under favorable environmental conditions and/or in the absence of the use of appropriate management practices, the proliferation of insects can reach levels of economic damage and cause losses.
In the 2012/2013 crop season there were reports on the occurrence of worm infestations in Brazil, the damages of which were observed in cotton and soybean crops in western Bahia, South of Maranhão and Piauí. In the Cerrado region, there are also reports of attacks on corn, cotton, beans, millet, sorghum and soybeans. The worms referred to belong to the species Helicoverpa spp., Heliothis virescens and Spodoptera spp.
Brazilian farmers have opted for the use of genetically modified seeds (GM) containing the Bt technology as an alternative to control pests. This technology is widely used in the country because of its efficiency. Moreover, it presents other advantages, such as: no adverse effects to non-target organisms, maintenance of biological control agents in nature, as well as the rational use of insecticides, resulting in social and environmental benefit due to the decreased risk of contamination by undue exposure.
With the increased adoption of this technology in corn and cotton and given the occurrence of insect attacks to Bt plants, the effectiveness of transgenic crops has been questioned. Therefore, some clarifications are needed to elucidate the reasons for the infestation, confirm the effectiveness of the technology and reinforce the recommendation of control measures.
Why is the pest pressure more intense this crop season?
Three factors contributed significantly to the occurrence of the infestation. The first is related to weather conditions, which in the 2011/2012 and 2012/2013 crop seasons were atypical. The drought favored the survival of larvae in the 2011/2012 crop season, which found suitable climatic conditions to complete their development cycle and thus ensure the survival and population increase.
The second factor can be assigned to sequential and simultaneous planting of host crops (such as maize, soybeans and cotton). Thus, these areas provide food, shelter and abundant breeding sites for the pests.
The third factor refers to the absence of adequate monitoring, which allows early identification of pest infestations. Detection of populations at the beginning of the infestation is essential for effective control, given that commercial insecticides and Bt plants are currently more effective in worms in early stages of development.
Why was Bt technology unable to control pest attacks?
Each technology is developed for one or a group of specific pests and each Bt trait shows different levels of control for different target species. It is important to mention that researchers from the Empresa Brasileira de Pesquisa Agropecuária [Brazilian Agricultural Research Corporation] (Embrapa) have found that one of the worms attacking cotton, corn and soybeans crops in various regions is the Helicoverpa armigera, which had not yet been found in Brazil. The identification of the pest was done through morphological analysis (from genitalia - undertaken by researcher Alexandre Specht – Embrapa Cerrados) and through molecular analysis (conducted by Daniel R. Sosa-Gomez - Embrapa Soja).
The Helicoverpa armigera is regarded as an A1 quarantine pest. This classification is given for exotic pests not present in the country, which can cause significant economic damage. The lack of correct identification of the pest population worsened the outbreak, as the registered insecticides and commercial Bt plants available in the country did not consider this species as a target pest.
With the identification of the quarantine pest, the Agriculture Defense Department of the Ministry of Agriculture, Livestock and Supply (MAPA) authorized on an emergency basis the import and application of products that have emamectin benzoate as the sole active ingredient. The use of this compound is authorized in over 40 countries, including Portugal, Spain, Italy, France, the Netherlands, the United States and Australia.
What are the recommendations for the management of Bt crops?
Even with the use of this technology, constant crop monitoring is necessary to check whether there is need for additional control. Under high pest pressure conditions, insecticide applications may be needed even on Bt crops. This is part of the Integrated Pest Management (IPM), a system that combines techniques and methods suitable for the maintenance of insect population at levels that would prevent economic damage.
In the current cropping system, in which the succession of crops is a common practice, the adoption of desiccation, where applicable, followed by the application of insecticides is extremely important. Furthermore, the rotation of active ingredients with different action mechanisms is recommended. This practice reduces the initial population of pests and worms in later stages of development, which can cause damage even to Bt crops.
Another IPM measure is the adoption of refuge areas - non-GM amidst GM plants – which are essential to keep the target pests susceptible to the Bt toxin. Refuge areas are crucial to the longevity of the technology, given that they represent a source of susceptible individuals, which are useful to prevent the emergence of resistance.
As a complementary practice, insecticide seed treatment is also recommended for plant protection in their early development stages.
Therefore, the use of GM plants for insect control is an effective and environmentally safe practice. However, in any production system, including those using GM plants, the other IPM control practices (chemical, biological and cultural) are paramount to maintaining the effectiveness and longevity of the technology. Proper management in agriculture should be the responsibility of all stakeholders involved in the supply chain.
i Daniela Brioschi, doctor in Genetics and Breeding - Escola Superior de Agricultura “Luíz de Queiróz” (ESALQ-USP) ii Dirceu Gassen, master in Agronomy in Plant Science - Rio Grande do Sul Federal University (UFRGS) iii Marcelo Gravina, doctor in Phytopathology and Molecular Biology - Rio Grande do Sul Federal University (UFRGS)
iv Odair Fernandes, doctor in Entomology - Nebraska Lincoln University (USA)