Comparative Screening of Mexican, Rwandan and Commercial Entomopathogenic Nematodes to Be Used against Invasive Fall Armyworm, Spodoptera frugiperda.

Patrick Fallet,Patrick Karangwa,Bancy Waweru,Thomas Degen,Pamela Bruno,Ted C J Turlings,Joelle Kajuga,Julio S Bernal,Ricardo A R Machado,Didace Bazagwira,Lara De Gianni,Stefan Toepfer

doi:10.3390/insects13020205

Abstract

Simple SummaryThe fall armyworm is a devastating insect pest of maize that has recently spread from the Americas to Africa and Asia. Synthetic insecticides are currently being used excessively to fight this pest. Safe, effective and more sustainable alternatives are urgently needed. We explore the use of beneficial entomopathogenic nematodes to control the fall armyworm. These tiny soil-born roundworms are lethal parasites of insects, including caterpillars such as the fall armyworm. We tested forty nematode strains from either the native range of the fall armyworm (Mexico), or the area of invasion (Rwanda), and commercial strains. We found that certain strains of local nematodes from the area of invasion can be as effective in infecting and killing fall armyworm as commercial strains or those from the armyworm’s native range. These findings will aid the development of locally acceptable and effective biological control products.The fall armyworm (FAW), Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) is an important pest of maize originating from the Americas. It recently invaded Africa and Asia, where it causes severe yield losses to maize. To fight this pest, tremendous quantities of synthetic insecticides are being used. As a safe and sustainable alternative, we explore the possibility to control FAW with entomopathogenic nematodes (EPN). We tested in the laboratory whether local EPNs, isolated in the invasive range of FAW, are as effective as EPNs from FAW native range or as commercially available EPNs. This work compared the virulence, killing speed and propagation capability of low doses of forty EPN strains, representing twelve species, after placing them with second-, third- and sixth-instar caterpillars as well as pupae. EPN isolated in the invasive range of FAW (Rwanda) were found to be as effective as commercial and EPNs from the native range of FAW (Mexico) at killing FAW caterpillars. In particular, the Rwandan Steinernema carpocapsae strain RW14-G-R3a-2 caused rapid 100% mortality of second- and third-instar and close to 75% of sixth-instar FAW caterpillars. EPN strains and concentrations used in this study were not effective in killing FAW pupae. Virulence varied greatly among EPN strains, underlining the importance of thorough EPN screenings. These findings will facilitate the development of local EPN-based biological control products for sustainable and environmentally friendly control of FAW in East Africa and beyond.

Highlights

The fall armyworm (FAW), Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) is a major pest of maize originating from the tropical and subtropical regions of the Americas [1].FAW is polyphagous, but prefers grasses, maize, sorghum and rice [1]
Andalo et al [17] reported that Steinernema riobrave was poorly effective against FAW, even at high concentrations (500 infective juveniles (IJs) per caterpillar), whereas we show that another S. riobrave was among the most effective strains in the present study (Figures 1–3; strain Mexicanin entomopathogenic nematode strains (MEX)-15)
We show in this study that entomopathogenic nematodes (EPN) isolated in the area of invasion of FAW can be as effective as area-of-origin or commercial EPNs to control FAW

Summary

Introduction

The fall armyworm (FAW), Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) is a major pest of maize originating from the tropical and subtropical regions of the Americas [1]. FAW is polyphagous, but prefers grasses, maize, sorghum and rice [1]. 2016, FAW was reported in West Africa and rapidly spread across the continent and further into Asia [2–5]. On both continents, it causes tremendous crop damages and yield losses [5–9]. To mitigate the impact of FAW, governments launched emergency programs and subsidized synthetic insecticides, which quickly became the backbone of FAW control in the invasive range [10–12]. Because of the environmental harm and health risks caused by these measures, safe, sustainable and effective alternative FAW control strategies are urgently needed [5]

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