Spodoptera frugiperda is an important pest throughout the Western Hemisphere, particularly in corn, cotton, rice, and sorghum, among other crops. This insect has evolved two strains named the corn and the rice strains, as they have been their most frequently used hosts. However, the corn strain can also be found in cotton and the rice strain in pasture grasses and corn. Both strains have been identified by using different molecular markers, including allozymes, polymerase chain reaction—restriction fragment-length polymorphism, amplified fragment-length polymorphism, and FR tandem repeat unit, among others. So far, all reports have claimed no morphological differences between the strains. However, none of these studies have used geometric morphometrics, as we performed in this work. We applied wing morphometrics to analyze wing size and shape in 159 individuals of the corn and the rice strains reared under laboratory conditions since 2009 and already genotyped. Our results demonstrated that wing morphometrics is a promising tool to differentiate both strains, as they were statistically significant in wing shape. We also found that this species presents sexual dimorphism in the rice strain in wing shape and that wing size differs between males of both strains. Further studies will require the use of this new tool in field populations, as their identification is relevant, given that they exhibit reproductive isolation and differences in susceptibility to chemical and biological controls, suggesting they are in the process of speciation via host plant association.
Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) represents a pest of economic importance in all Western Hemisphere. This polyphagous species has diverged into two populations that have been mainly recognized with various mitochondrial and nuclear molecular markers and named "the rice" and "the corn" strains. In Colombia, both strains have evolved prezygotic and postzygotic isolation. They differ in tolerance to Bacillus thuringiensis (Cry1Ac and Cry1Ab endotoxins) and the insecticides lambda-cyhalothrin and methomyl. In 2014, a wing morphometric analysis made in 159 individuals from a colony showed that both strains significantly differ in wing shape. The species also exhibits sexual dimorphism in the rice strain as in females wing size is larger than in males. Here, we continued this work with another wing morphometric approach in laboratory-reared strains to calculate wing size and shape heritabilities using a full-sib design and in wild populations to determine if this method distinguishes these strains. Our results show that male heritabilities of both traits were higher than female ones. Wild populations were significantly different in wing shape and size. These results suggest that wing morphometrics can be used as an alternative method to molecular markers to differentiate adults from laboratory-reared populations and wild populations of this pest, particularly in males of this species. Finally, Q ST values obtained for wing size and shape further demonstrated that both strains are genetically differentiated in nature.
Habitat change in Rhodnius spp may represent an environmental challenge for the development of the species, particularly when feeding frequency and population density vary in nature. To estimate the effect of these variables in stability on development, the degree of directional asymmetry (DA) and fluctuating asymmetry (FA) in the wing size and shape of R. prolixus and R. robustus-like were measured under laboratory controlled conditions. DA and FA in wing size and shape were significant in both species, but their variation patterns showed both inter-specific and sexual dimorphic differences in FA of wing size and shape induced by nutrition stress. These results suggest different abilities of the genotypes and sexes of two sylvatic and domestic genotypes of Rhodnius to buffer these stress conditions. However, both species showed non-significant differences in the levels of FA between treatments that simulated sylvan vs domestic conditions, indicating that the developmental noise did not explain the variation in wing size and shape found in previous studies. Thus, this result confirm that the variation in wing size and shape in response to treatments constitute a plastic response of these genotypes to population density and feeding frequency.
This study aimed to determine the nutritional value of the fatty acids in the freshwater fish Prochilodus magdalenae, Pseudoplatystoma magdaleniatum and Ageneiosus pardalis during dry and wet Neotropical seasons with the view to generate useful information for nutrition and sustainable commercial exploitation. The analysis of fatty acids was performed by gas chromatography–mass spectrometry and the nutritional value was calculated using five estimators: n-6/n-3 ratio, unsaturation index (UI), atherogenicity index (AI), thrombogenicity index (TI) and ratio of hypocholesterolemic/hypercholesterolemic (h/H) fatty acids. A different number of fatty acids (P. magdaleniatum = 50, P. magdalenae = 41, and A. pardalis = 32) was identified for each species and the average abundance percentages were different in the two seasons (p < 0.05). Prochilodus magdalenae and P. magdaleniatum showed healthy n-6/n-3 ratios (1.04 and 2.72) in the different seasons. Although the three species showed low values of UI (0.37–0.63), the remaining nutritional indexes were within the healthy range (AI: 0.04–0.70, TI: 0.66–1.07, h/H: 0.80 – 24.40). Multivariate analysis showed similar healthy nutritional values for the species, with exception of P. magdaleniatum.
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