No abstract

Lepidoptera, stink bugs, and weevils are important pests in soybean. For lepidopteran control, insecticides and seed treatments are used. As an alternative, Bt soybean was developed to control primary pests of Lepidoptera such as Rachiplusia nu (Guenée) (Noctuidae), Chrysodeixis includens (Walker) (Noctuidae), Anticarsia gemmatalis Hübner (Erebidae), Helicoverpa gelotopoeon (Dyar) (Noctuidae), and Crocidosema aporema (Walsingham) (Tortricidae). However, the use of transgenic plants, and the resulting reduction of insecticide against target pests, may allow other pest species to become more prevalent in agricultural environments. Soybean expressing Cry1Ac against different lepidopteran nontarget and target insect pests was evaluated, and its performance was compared with non-Bt soybean with seed treatment. The treatments were Bt soybean, non-Bt soybean with seed treatment (Fortenza® diamide insecticide, Syngenta, Buenos Aires, Argentina), and non-Bt soybean without seed treatment. Larvae of H. gelotopoeon, Spodoptera albula (Walker) (Noctuidae), Spodoptera cosmiodes (Walker) (Noctuidae), Spodoptera eridania (Stoll) (Noctuidae), and Spodoptera frugiperda (J. E. Smith) (Lep.: Noctuidae) were used. The plants of each treatment were infested with larvae of each species, and the percentage of leaf damage produced by each species was recorded. The results showed that Bt soybean provided control of H. gelotopoeon and had a suppressive effect on S. frugiperda and S. albula. However, S. eridania and S. cosmiodes were not susceptible to the Cry1Ac protein in MON 87701 × MON 89788 soybean when evaluated by greenhouse infestation. Considering the performance of each species using non-Bt soybean without seed treatment, S. eridania would represent a potential risk in soybean crops.

Spodoptera frugiperda (J. E. Smith) is one of the major pests of maize in Argentina. The main tool for its control is the use of genetically modified maize hybrids expressing Bacillus thuringiensis (Bt) insecticidal proteins. Maize growers in Argentina initially controlled this pest with Bt maize that expressed a single Bt protein (Cry1Ab or Cry1F). Currently it is necessary to plant maize cultivars that produce two Bt proteins to achieve the satisfactory control. Recently, Cry1F field-evolved resistant populations of this species were confirmed in Argentina. The objective of this study was to evaluate the performance of S. frugiperda field-collected strains on different Bt and non-Bt maize hybrids. Strains were collected from non-Bt maize (T1), Agrisure TDMax (T2), Agrisure Viptera (T3), Agrisure Viptera 3110 (T4), Genuity VT Triple Pro (T5), and Power Core (T6). Three experiments were performed to 1) determine the survivorship and reproduction of field-collected larvae (F0) from Bt maize hybrids, 2) evaluate Cry1F resistance using an F1 screen, and 3) assess the performance of F1 strains on different maize hybrids. In the F0, the survivorship from larva to adult ranged from 0 to 63%. We obtained adults from only the T1, T2, T5, and T6 strains with no significant differences in the reproductive parameters. Continuously rearing F1 larvae on their collected hosts affected larval duration, which was significantly shorter for a known-laboratory Bt-susceptible strain than the field-collected strains. Our results support the existence of Cry1F-resistance alleles in S. frugiperda field populations in Argentina.

The sugarcane borer, Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae), is one of the main lepidopteran pests of sugarcane and maize. The association of insects with different environments and/or host plants may occur by adaptation and this can generate host races. Adaptation may produce phenotypic or genotypic variation, which results in the differences in bioecological characteristics such as reproductive compatibility that reduces gene flow among populations. The objective of this study was to determine the reproductive compatibility of three population combinations collected in various geographic locations and from different host plants, thereby determining the influence of geographic distance and/or insect plant association. Interpopulation crosses of D. saccharalis populations from Tucumán (maize and sugarcane) and Jujuy (sugarcane) provided evidence of pre‐zygotic and post‐zygotic incompatibility. The results indicate that gene flow barriers are influenced by the host plant. However, populations from various locations revealed that geographical location is the main factor influencing gene flow among populations of D. saccharalis.

The Asian soybean stem borer Melanagromyza sojae (Zehntner) (Diptera: Agromyzidae) represents a threat to soybean and chickpea crops in South America. It is known that in the region its population has increased, in part, due to the difficulty in its agronomic management. This is due to the lack of knowledge regarding its biology and the environments that are favorable for its establishment. In this study, we provide a comprehensive database of records of M. sojae, as well as an updated list of its host plants from field surveys, bibliographic review, and online databases. We estimated the suitability and potential distribution of the pest considering environmental information from remote sensors and bioclimatic variables and contrasted these against land‐use cover across South America. In Argentina, M. sojae was found developing on Tithonia tubaeformis (Jacq.) Cass. (Asteraceae), surviving in chickpeas and volunteer soybeans that were affected by winter frost. The most informative models and highest suitability were predicted from vegetation indices and bioclimatic variables, and coincided with sites having a high proportion of arable land. Regarding climate, the greatest suitability occurred in eastern South America, including the southern states of Brazil and Paraguay, where the final models recovered the current known distribution of the species on the continent. However, its extension may be even greater than predicted, due to the wide distribution range of its hosts. This characterization of suitability for M. sojae could be a useful resource to anticipate the regions that are most favorable for its presence and supports the need to consider the distribution of crops and host plants that could act as natural reservoirs to identify sites and streamline efforts to reduce the incidence of the pest.