Host Association of Spodoptera frugiperda (Lepidoptera: Noctuidae) Corn and Rice Strains in Argentina, Brazil, and Paraguay

Abstract

Spodoptera frugiperda (J.E. Smith) is composed of two genetically distinct strains, the so-called corn strain and the rice strain. Whether the two strains differ in their host use is unclear, because laboratory experiments have not been able to show consistent host performance or preference differences between them, and field studies showed high rates of hybridization, as well as some degree asymmetric host use. To determine the distribution of the two strains and their association with host plants, we collected fall armyworm larvae from different crops (corn, rice, alfalfa, and sorghum) and grasses in 15 different localities over 4 yr in Argentina, Brazil, and Paraguay. The strain identity was analyzed using two polymorphisms in the mitochondrial cytochrome oxidase subunit I gene. We identified the corn and rice haplotypes and three types of populations were characterized based on the frequencies of the individuals that belonged to any of these haplotypes: in 44% of populations the corn haplotype predominated, in 44% of populations the rice haplotype was the most frequent, and 11% of populations showed both haplotypes at similar proportions. In total, eight populations (47%) showed the expected pattern, two populations (12%) were polymorphic within the same field, and seven populations (41%) showed the inverse pattern. Taken together, there was no consistent pattern of host association between the two sympatric genotypes and their respective host plants. This investigation supports the need for additional studies to determine which other forces keep the genotypes separate, and what is the degree of genetic differentiation between these populations.

Reproductive potential of Spodoptera eridania (Stoll) (Lepidoptera: Noctuidae) in the laboratory: effect of multiple couples and the size

“…These results are similar to the highest values of fertilization obtained in experiments using S. frugiperda when various couples were maintained in each cage (N= 25) (Milano et al, 2008), and are higher than those obtained by Juárez et al (2012), who evaluated different populations of the same species using only one couple per cage. (Kaplan-Meier) and confidence intervals of Spodoptera eridania moths emerged from small, medium-sized and large pupae.…”

Molecular methods to detect Spodoptera frugiperda in Ghana, and implications for monitoring the spread of invasive species in developing countries

“…frugiperda occurred in two races, a ‘rice strain’ (R strain) and a ‘corn strain’ (C strain) 10 ; the former is thought to preferentially feed on rice and various pasture grasses and the latter on maize, cotton and sorghum, although this may be geographically variable, e.g. this is not consistent in Argentina 11 . The strains are morphologically identical, but can be distinguished using DNA barcodes 12 which show two distinct clusters 13 that may have diverged 2 myr ago and now have a mean sequence divergence of 2.09% 14 .…”

Genetic basis of allochronic differentiation in the fall armyworm

“…So far, three possible prezygotic mating barriers have been described in this species: a) differential host plant choice [19–23], b) strain-specific timing of mating in the night [15, 16], and c) female sex pheromone differences [24–26]. Recent studies have shown that host preference in the field is not as specific as previously thought [27–29]. Therefore, habitat isolation seems to be a relatively weak prezygotic mating barrier.…”