Field‐evolved resistance to Cry1Ac Bt soybean in Rachiplusia nu (Lepidoptera: Noctuidae) from Argentina

PAEZ JEREZ, PAULA; HILL, JORGE GUILLERMO; HERRERA LINARES, FACUNDO; ROBLES TERÁN, LUIS; VERA MARIA TERESA

La Plata

Congreso; XI Congreso Argentino y XII Congreso Latinoamericano de Entomología; 2022

UNIVERSIDAD NACIONAL DE LA PLATA, CEPAVE-CONICET, FELA, MUSEO DE LA PLATA, SEA

Since its introduction in Argentina in 2013, Bt soybean has been one of the most powerful technologies to control insects and weeds. However, over time, the selection pressure favors the appearance of resistant pest populations. Recently, an increasing of abundance of Rachiplusia nu (Lepidoptera: Noctuidae) populations, which are frequently controlled by Bt toxin, were observed feeding on Bt soybean plants in Chaco, Santiago del Estero, Tucumán and Catamarca, Argentina. In this work, we compared the larval survival from two different R. nu populations, a field population found on Bt soybean (FIE) and a laboratory population (LAB). In addition, we tested the oviposition preference of both moth populations on Bt and non-Bt soybeans. Third-instar larvae were put into the glass tubes with Bt and non-Bt fresh leaves. Three days later, the number of alive and death larvae was recorded. Then, the surviving larvae were placed into tubes and fed with artificial diet, and their survival was recorded each three days until all larvae had died or reached the pupal stage. The oviposition preference was tested using two potted soybean plants, Bt and non-Bt, in a choice experiment which were enclosed into cages built with “voile” fabric. A total of five R. nu couples were released in each cage. The number of eggs laid was counted daily until moths’ death. Larval survivals were analyzed using nonparametric Kaplan–Meier analysis. The number of eggs laid was modelled using a zero-inflated count model with negative binomial distribution. We used as factors the soybean variety and population identity (FIE and LAB). The interaction between factors was also compared. Survival analysis showed significant differences between populations as well as soybean varieties. Rachiplusia nu FIE larvae fed on Bt and non-Bt soybeans and R. nu LAB larvae fed on non-Bt soybean had higher survival rates than R. nu LAB fed on Bt soybean. Interestingly, both populations laid a higher number of eggs on Bt soybean than non-Bt plants. Our results suggest that R. nu FIE populations’ abundance is expected to increase in Bt-soybean agroecosystems given both its host preference and capacity to tolerate Bt toxins. Alternative approaches to manage insect resistance are warranted.