The fall armyworm strain associated with most rice, millet, and pasture infestations in the Western Hemisphere is rare or absent in Ghana and Togo
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Date
2021
Journal Title
Journal ISSN
Volume Title
Publisher
PLOS
Abstract
The moth pest fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)
is now present throughout much of the Eastern Hemisphere where it poses a significant eco nomic threat to a number of crops. Native to the Western Hemisphere, fall armyworm is one
of the primary pests of corn in the Americas and periodically causes significant economic
damage to sorghum, millet, cotton, rice, and forage grasses. This broad host range is in part
the result of two populations historically designated as host strains (C-strain and R-strain)
that differ in their host plant preferences. Reports of infestations in Africa have to date mostly
been limited to the C-strain preferred crops of corn and sorghum, with little evidence of an
R-strain presence. However, this could reflect a bias in monitoring intensity, with the R-strain
perhaps being more prevalent in other crop systems that have not been as routinely exam ined for the pest. Because knowledge of whether and to what extent both strains are present
is critical to assessments of crops at immediate risk, we analyzed specimens obtained from
a systematic survey of pasture grass and rice fields, habitats typically preferred by the Rstrain, done contemporaneously with collections from corn fields in Ghana and Togo. Substantial larval infestations were only observed in corn, while pheromone trap capture numbers were high only in corn and rice habitats. Little to no fall armyworm were found in the
pasture setting. Comparisons with a meta-analysis of studies from South America identified
differences in the pattern of strain-specific markers typically found in fall armyworm collected
from rice habitats between the two hemispheres. Genetic tests of specimens from rice and
corn area traps failed to show evidence of differential mating between strains. These results
are consistent with the R-strain being rare or even absent in Africa and, at least for the
Ghana-Togo area, this R-strain lack does not appear to be due to limitations in pest monitoring. The implications of these results to the crops at risk in Africa and the accuracy of existing molecular markers of strain identity are discussed.
Description
Research Article