Caterpillars develop resistance; Biotechnologies and insecticides lose efficiency in Brazil

Caterpillars that are difficult to control, such as Spodoptera frugiperda (fall armyworm) and Helicoverpa zea (corn earworm), are increasingly adapting to crops, forcing many Brazilian farmers to change their practices to reduce their losses in grain production. This information was exclusively revealed to AgroPages by Eduardo Barros, a researcher with Supera Soluções Agronômicas, a consultancy operating in the Brazilian states of Bahia, Mato Grosso, Mato Grosso do Sul, Goiás, Maranhão, and Piauí.

Barros warns that there are known cases where farmers have done a good job with fertilization, seed selection, and disease management, but neglected caterpillar control. By the time they realized the problem, the damage was already done, with losses ranging from 10 to 15 sacks of soybeans per hectare, he notes.

Further, according to Barros, there are scenarios in which farmers ″fail to consider the economic importance associated with caterpillars that target the reproductive structures of crops. Spodoptera and zea feed on corn ears, cotton reproductive structures, and soybean pods. They are silent pests, often acting without being noticed.″

″So far, transgenic Bt, Cry, and VIP biotechnologies, as well as insecticides, have, in general, contributed significantly to the control of lepidopteran pests. However, the breakdown of resistance to these technologies now demands precise measures for the effective management of ‘reproductive structure caterpillars,’ especially Spodoptera and zea. They’re not just eating leaves; they’re eating what farmers sell, the final product,″ noted Barros.  

 Additionally, said Barros, the intensification of losses caused by these caterpillars was first observed in Bahia, Piauí, and Maranhão. Today, he noted, the spread of both species is evident in nearly all soybean, corn, and cotton-growing areas, including Goiás, Tocantins, Mato Grosso, and Mato Grosso do Sul.

Barros added that, given the advance of these caterpillars across the country, the first thing farmers must do is ″accept that the technologies are no longer the same.″ ″There are transgenic plants that are ceasing to work, and insecticides that are delivering far less. One of the tools available to farmers is thorough monitoring to ‘know their enemy,’″ he said.

 Barros also recommends ″adopting the use of traps with food attractants (‘attract-and-kill’), which can identify the species and population of caterpillars present in a given area, ideally before the crop emerges.″

″Targeting adult females before they lay eggs is better than battling millions of caterpillars later,″ Barros said. He explains that this approach involves using products containing plant extracts combined with 2% chemical insecticides. The solution attracts moths, which die upon ingesting the compounds before laying eggs in the field. Consequently, this prevents the emergence of caterpillar populations at economically damaging levels.

Through monitoring, Barros adds, farmers can also determine when to apply specific treatments in the field to achieve effective control, especially when facing significant caterpillar populations in crops.

Regarding the main treatments recommended for controlling Spodoptera frugiperda and Helicoverpa zea populations, Barros states that he has achieved favorable results by rotating chemical insecticides with different active ingredients and incorporating biological products into management practices. ″For these caterpillar species, we’ve noticed that viruses, or baculoviruses, due to their specificity and potency, have been highly effective,″ added Barros.

(Editing by Leonardo Gottems, reporter for AgroPages)