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

Matthew J W Cock,Giovanni Cafá,Jayne Crozier,Patrick K Beseh,Alan G Buddie

doi:10.1038/s41598-017-04238-y

Matthew J W Cock, Giovanni Cafá + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-04238-y

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Abstract

Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a polyphagous pest indigenous throughout the Americas, which recently appeared in Africa, first reported from São Tomé, Nigeria, Bénin and Togo in 2016, and which we now report from Ghana. This species is recognised to comprise two morphologically identical but genetically distinct strains or species in the Americas, and we found both to be present in Ghana. We discuss possible routes of entry to Africa, of which the likeliest is adults and/or egg masses transported on direct commercial flights between the Americas and West Africa, followed by dispersal by adult flight within Africa. Identification of Lepidoptera is normally based on the markings and morphology of adults, and not on the larvae which actually cause the damage, and therefore larvae have to be reared through to adult for authoritative identification. We confirmed that the use of DNA barcoding allowed unequivocal identification of this new pest from Ghana based on the larvae alone. As authenticated barcodes for vouchered specimens of more pests become available, this approach has the potential to become a valuable in-country tool to support national capability in rapid and reliable pest diagnosis and identification.

Highlights

For clarity we choose to refer to the two barcode clusters as species: S. frugiperda sp. 1 (ACE4782) and S. frugiperda sp. 2 (AAA4532)
Photographic images of the pest sent to CABI UK by a Plantwise plant doctor were not sufficient alone to substantiate an identification of this New World species as a new pest for Ghana and the plant doctor was asked to provide further images and preserved adult specimens if possible, and the PPRSD became aware of this potential new pest at this time
The analysis of our collections from three regions in Ghana has shown that both species of S. frugiperda are widespread attacking maize, we did not find S. frugiperda sp. 2 (AAA4532) in the five S. frugiperda samples sequenced from Brong Ahafo

Summary

Introduction

Smith) (Lepidoptera: Noctuidae) is a polyphagous pest indigenous throughout the Americas[1, 2], which has recently appeared in Africa[3], and we have detected in Ghana It is regularly intercepted in intercontinental trade[4] but has not previously become established outside the Americas (a report of its presence in Israel[5] was based on a misidentification)[2]. The two species or strains are sympatric, continuously breeding from southern USA to northern Argentina, and both occur as temporary breeding immigrant populations further north and further south during summer and autumn, but are unable to tolerate freezing temperatures Whether these two clusters represent two interbreeding races, two separating species, two separated populations that are merging, or two separate species is not yet entirely clear, but the most recent studies[14, 17, 18] incline towards the last view, with reproductive isolation between the two species in at least part of their range.

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