Large-scale assessment of lepidopteran soybean pests and efficacy of Cry1Ac soybean in Brazil

Abstract

The soybean technology MON 87701 × MON 89788, expressing Cry1Ac and conferring tolerance to glyphosate, has been widely adopted in Brazil since 2013. However, pest shifts or resistance evolution could reduce the benefits of this technology. To assess Cry1Ac soybean performance and understand the composition of lepidopteran pest species attacking soybeans, we implemented large-scale sampling of larvae on commercial soybean fields during the 2019 and 2020 crop seasons to compare with data collected prior to the introduction of Cry1Ac soybeans. Chrysodeixis includens was the main lepidopteran pest in non-Bt fields. More than 98% of larvae found in Cry1Ac soybean were Spodoptera spp., although the numbers of Spodoptera were similar between Cry1Ac soybean and non-Bt fields. Cry1Ac soybean provided a high level of protection against Anticarsia gemmatalis, C. includens, Chloridea virescens and Helicoverpa spp. Significant reductions in insecticide sprays for lepidopteran control in soybean were observed from 2012 to 2019. Our study showed that C. includens and A. gemmatalis continue to be primary lepidopteran pests of soybean in Brazil and that Cry1Ac soybean continues to effectively manage the target lepidopteran pests. However, there was an increase in the relative abundance of non-target Spodoptera spp. larvae in both non-Bt and Cry1Ac soybeans.

Resistance status of lepidopteran soybean pests following large-scale use of MON 87701 × MON 89788 soybean in Brazil

“…were nearly absent from MON 87701 × MON 89788 soybean fields, showing the consistent efficacy of MON 87701 × MON 89788 soybean in managing these lepidopteran species. Our results also demonstrate that C. includens and A. gemmatalis remain the most abundant primary lepidopteran pests in non- Bt soybean fields, confirming the results from previous research 7 . These species were widely distributed across the soybean-growing regions of Brazil, whereas R. nu , Helicoverpa spp.…”

“…Historically, R. nu has been a soybean pest in the southern part of South America (Rio Grande do Sul state in Brazil, Uruguay and Argentina) 24 , 26 , 45 . In a prior field survey in 2019 and 2020, R. nu occurred at a low level in Brazil 7 . However, R. nu has increased in abundance in soybean areas at lower latitudes, which may indicate an adaptation of R. nu populations to warmer climate conditions before evolving resistance to MON 87701 × MON 89788 soybean.…”

“…Moreover, the lack of adoption of Integrated Pest Management (IPM) practices, particularly in refuge areas, can increase the spraying of foliar insecticides in these areas, thus reducing the effectiveness of this important IRM strategy and favoring pest resurgence by likely reducing the abundance of biological control agents 46 . Despite the characteristics of R. nu and C. aporema that might have favored resistance development, the question remains why Cry1Ac resistance to MON 87701 × MON 89788 soybeans evolved in these species but not in C. includens, the most abundant lepidopteran soybean pest in Brazil 7 , under the same refuge adoption and management settings as these other pests. The absence of field-evolved Cry1Ac resistance in C. includens in Brazil suggests that the mechanisms of Cry1Ac resistance in C. includens may be more complex and detrimental to fitness than those in R. nu (or C. aporema ).…”

“…The high adoption rate of MON 87701 × MON 89788 soybean has been driven by the significant yield advantage of varieties containing this technology and the high levels of protection against the primary soy lepidopteran pests in Brazil. MON 87701 × MON 89788 soybean provides effective protection against larval feeding by Anticarsia gemmatalis (Hübner, 1818) (Lepidoptera: Erebidae), Chrysodeixis includens (Walker, [1858]), Chloridea virescens (Fabricius, 1781) and Helicoverpa armigera (Hübner, 1808) (Lepidoptera: Noctuidae) 4 – 7 .…”

The role of genetically engineered soybean and Amaranthus weeds on biological and reproductive parameters of Spodoptera cosmioides (Lepidoptera: Noctuidae)

“…Thus, ecological niches that were not accessible because of interspecific competition or the application of synthetic insecticides, are now occupied by other phytophagous species that tend to increase their population levels and may become economically important pests. For instance, the abundance of armyworms of the Spodoptera Guenée genus in soybean crops has increased in past years, and this change coincides with the greater use of Bt varieties 8–10 . The black armyworm, Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae), is a frequently encountered species occurring in several countries in South America, such as Brazil, Paraguay and Argentina 9–12 .…”