Argentina on alert after loss of effectiveness of soybeans with Bt technology

The Pest Management Network of Aapresid (Argentine No-Till Farmers Association) wrote an article highlighting a growing decline in the performance of Bt technology (Bacillus thuringiensis) in controlling Lepidoptera.

Since 2012, the use of Bt technology in soybean, which is capable of producing this protein and fighting pests that feed on it, has been approved in Argentina.

Since its approval, Argentine producers have increasingly adopted the technology, since it facilitates the control of pests with less use of insecticides. A survey showed that Bt technology in soybeans has been adopted in 70% of total area for both the 2021/2022 and 2020/2021 seasons.

The survey also showed a decline in the perceived performance of the technology among users, with 89% of those surveyed today rating Bt soy performance at between bad and satisfactory.

Many of those who in previous campaigns described it as an outstanding strategy for insect management began to observe the presence of Lepidoptera, such as Rachiplusia nu and Chrysodeixis includens, while monitoring their Bt soybean lots.

But the survey’s scope is not limited to just the presence of some species of Lepidoptera. In many cases, damage was seen in 56% of the Bt soybean area treated with foliar insecticides.

Technicians from the EEAOC (Bishop Colombres Agroindustrial Experimental Station) collected larvae in the affected lots, which were fed in the laboratory with Bt soybean leaves. A total of 60% of these larvae completed their life cycle, highlighting a drop in the vulnerability of the species to the technology.

Changes were also observed in the duration of the larval cycle of susceptible larvae. The same situation was recently corroborated in Brazil.

The agronomist, Enrique Lobos, stressed that in the area he looks after, fields planted with Bt soybeans account for around 60% of total, and the remaining crop area without this technology requires two to three applications to control Lepidoptera.

Lobos affirmed that producers and advisers in the area already assume a failure of the technology and consider that, under these circumstances and depending on the pest, Bt soybeans will tend to require the application of insecticides to control Lepidoptera. However, he maintains that, despite this failure, the technology will maintain acceptable levels of control, so a single application of insecticide could be enough.

Trials conducted in the area in the 2021/2022 season revealed a 95% presence of C. includens (false gauge) in the Lepidoptera population in Bt soybean lots, with populations of 15 individuals per meter and a surprising level of defoliation of up to 20%.

The agronomist, Diego Szwarc, from the National Institute of Agricultural Technology (INTA) said the problem in the Reconquista zone is quite general.

There is still a need to collect information, and for this reason, the station is launching a series of investigations to clarify the problem in cases where a break-in resistance is suspected, he added.

In mid-2021, Bayer suspended its soybean seed and biotechnology business in Argentina, claiming that it only represented 10% of the total area planted with INTACTA RR2 PRO in South America in the 2020/2021 season.

(Editing by Leonardo Gottems, reporter for AgroPages)