Embrapa Soja provides guidance on the management of armpit borer resistant to Bt soybeans in the 22/23 harvest

Embrapa Soja has just updated the technical note with guidance on the management of the armpit borer caterpillar (Crocidosema aporema) resistant to Bt soybeans, in the 22/23 harvest. The pest has a low potential to cause economic loss, which is why Embrapa Soja is recommending that producers monitor their areas and only choose to use synthetic chemical insecticides when 50% or more of the plants show symptoms of attack.

“Applying chemical insecticides before this infestation does not bring benefits to productivity and, therefore, is not economically justifiable”, explains the head of Research & Development at Embrapa Soja, Adeney de Freitas Bueno.

Surveys by Embrapa Soja show that populations of armpit borer resistant to the insecticidal protein Cry1Ac, present in Bt soybeans, have occurred, mainly in the central-north region of the state of Paraná and south of the state of São Paulo, favored by the occurrence of summers in some regions. Other soybean-producing regions, especially those facing dry weather, may experience the problem.

Bueno explains that despite the concern of many producers, the armpit borer has little capacity to reduce soybean productivity. “In experiments carried out during the 2020/21 and 2021/22 harvests, Embrapa Soja compared the productivity of plants with symptoms of attack with plants without any symptoms of attack in 13 different crops in the country. Only in one of the areas evaluated (Cristalina, GO), the production observed in plants with attack was lower when compared to plants without attack”, explains Bueno

History

The first generation of Bt soybeans approved in Brazil (Intacta RR2 Pro) was made commercially available to farmers in 2013 as a technology for the management of some target caterpillars: soybean caterpillar (Anticarsia gemmatalis), false caterpillar (Chrysodeixis includens), cotton bollworm (Chloridea virescens) and armpit borer (Crocidosema aporema). In recent harvests, Embrapa Soja has been monitoring the occurrence of populations of two species of caterpillars (Rachiplusia nu e Crocidosema aporema) resistant to the insecticidal protein Cry1Ac, expressed by the first generation of Bt soybeans.

In addition to constant monitoring of the area, Embrapa Soja recommends the adoption of a structured refuge area for soybean cultivation: planting at least 20% of non-Bt soybeans sown 800 m away from a Bt plant.

“In a scenario of high adoption of Bt-soy technology and low adherence to the practice of structured refuge, the probability of resistance evolution in target species increases considerably”, highlights Bueno.

The technical note can be read at the link below: