BACKGROUND: Spodoptera frugiperda is a destructive pest that often imposes difficult management due to its high polyphagy and rapid insecticide resistance evolution. Knowledge of species diversification, population structure, and host preference can aid efforts to manage pest populations. Here, we investigated the patterns of hybridization, genetic structure, and gene flow in S. frugiperda populations, discussing how we can apply this knowledge to insect resistance management programs in South America.
RESULTS:The corn-strain CS-h2 of S. frugiperda was the most frequent haplotype in all sampled populations. Spodoptera frugiperda populations are experiencing demographic expansion, and the ecoregions partially explain the genetic structure and not strains. We did not find a correlation between gene flow and susceptibility levels to flubendiamide and lufenuron insecticides, but populations with high LC 50 sent a great number of migrants to all other locations, maintaining resistance alleles in the geographic range. CONCLUSION: High levels of population admixture, including between corn-and rice-strains, were found in sampled populations. We showed that S. frugiperda immigrants will not necessarily cause an increase in LC 50 upon arrival in a new location but will assure the constant presence of resistance alleles in the area. Increases in LC 50 largely depend on the local pesticide management adopted in the areas. Our results indicate that pesticide resistance management must be adopted on a local or small regional scale.
Several specimens collected in Paraguay along with Anastrepha fraterculus (sensu lato) have an aculeus tip similar to species from the fraterculus complex, but the teeth of the aculeus of these specimens are poorly defined. As Anastrepha species identification is based mostly on subtle differences in the aculeus tip, we studied these specimens with atypical aculeus tips (with poorly defined teeth) that slightly differs from the aculeus tip of species of the fraterculus complex (with well-developed blunt teeth), to determine if this is due to intraspecific variation or if it can characterize a full species. The Paraguayan specimens were separated in six groups under stereomicroscope according to variation in their aculeus tip. Specimens within each group were studied by means of morphometrics (traditional and geometric) and gene sequence analysis (COI and ITS1). Morphometric analyses were significant, but no clear groups were formed by the discriminant analyses of the aculeus and wing, and the COI and ITS1 sequence analysis clustered specimens with all six aculeus variations. Therefore, the subtle morphological differences observed in the aculeus tip of Paraguayan specimens are intraspecific variations and the Paraguayan specimens were more genetically closely related to Anastrepha sp. 3 from the fraterculus complex.
ABSTRACT. The transgenic maize that expresses the Bt protein is one of the strategies most used for the control of Spodoptera frugiperda, key pests of this crop in America. With the objective of verifying the susceptibility of S. frugiperda; toxicity studies were conducted of the proteins Bt expressed in leaves of different events of maize released in Paraguay, 2B587hx™ (cry1F); VT triple PRO™ (Cry1A/Cry2Ab/Cry3Bb) and Formula TL™ (Cry1Ab). The rearing of S. frugiperda was conducted in the laboratory to obtain a uniform population under controlled conditions of temperature (25 ± 2°C), relative humidity (60 ± 10%) and photoperiod of 14:10 h (L:D). Mortality was evaluated and in the case of survivors; the weight and length of the pupae, the fertility of the females, the longevity of the adults, the viability of eggs, and the duration of the different stages and the total cycle. The supply of larvae neonates in the leaves of maize of the event VT triple PRO™ produced 100% mortality; however, in the larvae fed with leaves of the events 2B587hx™ and Formula TL™; the mortality was 58% and 56%, respectively. The survivors to these treatments had a longer life cycle, fertility and reduced fertility.
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