EBC, 29/05/2015  [áudio disponível no link]

Produtores rurais de Mato Grosso têm elevado o uso de inseticida no milho

69% dos produtores rurais de Mato Grosso estão realizando elevado número de aplicações de inseticida no milho semeado
Cerca de 69% dos produtores rurais de Mato Grosso estão realizando elevado número de aplicações de inseticida no milho semeado com a tecnologia Bt. A constatação foi feita no Circuito Tecnológico – Etapa Milho, evento organizado pela Associação dos Produtores de Soja e Milho de Mato Grosso (Aprosoja).O resultado foi obtido com a aplicação de questionários quantitativos, além da coleta de amostras de talhões de milho em todo o Estado no mês de abril. Para especialistas, isso pode evidenciar que a tecnologia está perdendo sua eficiência e, por isso, demandando maior uso de defensivos para combate às pragas. Sobre o assunto, o programa Nossa Terra conversou com gerente de planejamento da Aprosoja, Cid Sanches.Ele explica que o milho Bt é uma espécie de milho transgênico.  Disse ainda que “esse é um dado que mostra que deve haver mais atenção. Estão aplicando altas doses de inseticida em um milho que não precisaria dessa tecnologia, e se isso ocorre, é porque a tecnologia de combate já não está mais tão eficiente”.
Abaixo segue resumo de pesquisa que mostra os mecanismos pelos quais as lavouras Bt acabam levando mais inseticidas.


Dear friends and colleagues,

Re: The impact of secondary pests on Bacillus thuringiensis (Bt) crops

A study published this year in Plant Biotechnology Journal focuses on the development and impacts of secondary pests on Bt crops. The review finds that the causes for secondary outbreaks in Bt crops are reduction in broad-spectrum insecticide applications, reduction of natural enemies and species replacement.

However, the authors conclude that regardless of the causes, if non-susceptible secondary pest populations exceed economic thresholds, farmers are likely to resort to insecticide spraying as their immediate solution. This would undermine the whole rationale for the introduction of Bt crops which was supposedly to mitigate the heavy dependence and overuse of insecticides that has been responsible for negative environmental and ecological impacts across the globe – “…farmers growing Bt crops will potentially recommence running on the insecticide treadmill observed in the 20th century … leading once again to the negative impacts of insecticides on the environment that it was hoped Bt crops would reduce”.

The study concludes with five major issues that require further exploration:

  1. Large-scale, multi-trophic and multi-species field studies to reveal the extent and potential of impacts on ecosystems as laboratory and/or single species studies may fail to capture the wider trophic impacts that occurs in field environment. Only a holistic knowledge of pests and the behaviour of natural enemies will enable the formulation of a sustainable IPM framework capable of effectively suppressing secondary pest outbreaks.
  2. The baseline for risk analysis studies should be adjusted. Until now, studies have used conventional cropping with insecticide treatments as the main basis for comparison of risk of Bt crops. However, this comparison should be broadened to include other scenarios, such as organic or untreated cropping systems.
  3. Economic studies should move towards a wider approach, taking into consideration farmers’ heterogeneity. This is especially relevant in developing countries, where institutional networks are weak, making the enforcement of laws, policies and agricultural recommendations less effective.
  4. To identify possible secondary pests and other non-target effects of Bt crops with insecticidal properties, data are needed on which arthropod species occur in a given agro-ecosystem. Hence, continuous, post-market and spatiotemporal monitoring is critical for rapid identification of the development of ecological problems.
  5. The importance of spatially dynamic, bio-mathematical and bio-economic multi-species models in pre- and post-GE crop risk assessment research has been recognized for sometime. Rigorous assessments of the present and future economic impacts, based on ecological constraints, are required to provide sound information to policymakers.

The summary of the article is reproduced below.

Plant Biotechnology Journal (2015), pp. 1–12 

Review article

The impact of secondary pests on Bacillus thuringiensis (Bt) crops 

Rui Catarino (1), Graziano Ceddia (2), Francisco J. Areal (1) and Julian Park (1)

(1)School of Agriculture, Policy and Development, University of Reading, Reading, UK

(2) Department of Public Governance and Sustainable Development, MODUL University, Vienna, Austria


The intensification of agriculture and the development of synthetic insecticides enabled worldwide grain production to more than double in the last third of the 20th century. However, the heavy dependence and, in some cases, overuse of insecticides has been responsible for negative environmental and ecological impacts across the globe, such as a reduction in biodiversity, insect resistance to insecticides, negative effects on nontarget species (e.g. natural enemies) and the development of secondary pests. The use of recombinant DNA technology to develop genetically engineered insect-resistant crops could mitigate many of the negative side effects of insecticides. One such genetic alteration enables crops to express toxic crystalline (Cry) proteins from the soil bacteria Bacillus thuringiensis (Bt). Despite the widespread adoption of Bt crops, there are still a range of unanswered questions concerning longer term agro-ecosystem interactions. For instance, insect species that are not susceptible to the expressed toxin can develop into secondary pests and cause significant damage to the crop. Here, we review the main causes surrounding secondary pest dynamics in Bt crops and the impact of such outbreaks. Regardless of the causes, if nonsusceptible secondary pest populations exceed economic thresholds, insecticide spraying could become the immediate solution at farmers’ disposal, and the sustainable use of this genetic modification technology may be in jeopardy. Based on the literature, recommendations for future research are outlined that will help to improve the knowledge of the possible long-term ecological trophic interactions of employing this technology.