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

Abstract

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.

Steinernema africanum n. sp. (Rhabditida, Steinernematidae), a New Entomopathogenic Nematode Species Isolated in the Republic of Rwanda

“…The type hosts are unknown as the nematodes of this genus can be hosted by different insect species ( Yan et al, 2016 ; Kajuga et al, 2018 ; Fallet et al, 2022 ) and were isolated from mixed soil samples by the Galleria baiting technique ( White, 1927 ; Bedding and Akhurst, 1975 ). Briefly, S. africanum n. sp.…”

Laboratory and field trials reveal the potential of a gel formulation of entomopathogenic nematodes as biocontrol against the fall armyworm (Spodoptera frugiperda)

“…As FAW larvae are above-ground pests, they rarely encounter soil-borne EPN and are therefore poorly adapted to resist them. This may explain why the caterpillars have been found to be highly susceptible to many species and strains of EPN (Acharya et al, 2020; Fallet et al, in press). EPN normally only reproduce inside an insect host, but they can also be mass produced in fermenters with cultures of their specific symbiotic bacteria or in semi-solid cultures.…”

Potential of Entomopathogenic Nematode HbSD as a Candidate Biocontrol Agent against Spodoptera frugiperda

“…Notably, infection for 24 h was enough to cause the 100% mortality of S. frugiperda at a concentration of 250 IJs per 5th stage larva. Although it has been reported that H. bacteriophora was virulent in many insect species, including S. frugiperda , its virulence and killing speed varied among strains within EPN species [ 41 ]. For instance, H. bacteriophora collected from Daedong Tech (Daegu, Korea) caused ~60% mortality in 3rd instar larvae and ~50% mortality in 5th instar larvae at a concentration of 50 IJs per larva for 72 h post-treatment [ 26 ].…”