ABSTRACT
BACKGROUND: The fall armyworm, Spodoptera frugiperda is a native species of the Americas. First detected in western and central Africa in early 2016, it has become one of the most serious invasive lepidopteran pests in many African and Asian countries. S. frugiperda has spread very quickly; however, there are no molecular-based, simple and accurate diagnostic tools for identification of this species in the field. Methods to identify invasive S. frugiperda are urgently needed because farmers and agricultural managers have no prior experience with this pest. RESULTS: Based on mitochondrial genome sequence alignment, a S. frugiperda-specific sequence region was identified in the transfer RNA-coding region between NADH dehydrogenase, ND3, and ND5. Using this unique region, species-diagnostic primers were designed and applied in a loop-mediated isothermal amplification (LAMP) assay and a conventional polymerase chain reaction to identify field-collected samples of S. frugiperda. The optimal incubation conditions for the LAMP assay were 61°C for 90 min with four LAMP primers; an additional loop primer increased the amplification efficiency. A response was obtained for a wide range of DNA concentrations in the LAMP assay and the minimum detectable DNA concentration was 10 pg. CONCLUSIONS: We developed a new LAMP-based molecular diagnostic method that it is easy to use and accurate. The LAMP assay was used with a DNA-releasing technique for larval and adult samples, without a DNA extraction step, by incubating the tissue sample at 95°C for 5 min. This method can be applied in intensive field monitoring of S. frugiperda and its ecological studies. © 2021 Society of Chemical Industry.
Subject(s)
Molecular Diagnostic Techniques , Nucleic Acid Amplification Techniques , Animals , Asia , Spodoptera/geneticsABSTRACT
The pest species Spodoptera frugiperda, which is native to North and South America, has invaded Africa in 2016. The species consists of two strains, the corn-strain and rice-strain, which differ in their sexual communication. When we investigated populations from Benin and Nigeria, consisting of corn-strain and rice-corn-hybrid descendants, we found no strain-specific sexual communication differences. Both genotypes exhibited the same pheromone composition, consisting of around 97% (Z)-9-tetradecenyl acetate (Z9-14:Ac), 2% (Z)-7-dodecenyl acetate (Z7-12:Ac), and 1% (Z)-9-dodecenyl acetate (Z9-12:Ac), they had similar electrophysiological responses, and all mated around three hours into scotophase. However, we found geographic variation between African and American populations. The sex pheromone of African corn-strain and hybrid descendant females was similar to American rice-strain females and showed higher percentages of the male-attracting minor component Z7-12:Ac. In addition, African males exhibited the highest antennal sensitivity towards Z7-12:Ac, while American males showed highest sensitivity towards the major pheromone component Z9-14:Ac. Increasing the production of and response to the critical minor component Z7-12:Ac may reduce communication interference with other African Spodoptera species that share the same major pheromone component. The implications of our results on pheromone-based pest management strategies are discussed.
