The fall armyworm (Spodoptera frugiperda, Lepidoptera: Noctuidae), which is native to the Americas, has recently invaded Africa and Asia. There, it has become a major pest of maize (Zea mays). The variety of methods used to assess feeding damage caused by its caterpillars makes it difficult to compare studies. In this paper, we aim at determining which leaf damage rating scales for fall armyworm are most consistently used for which purposes, might provide most possibilities for statistical analyses, and would be an acceptable compromise between detail and workload. We first conducted a literature review and then validated the most common scales under field and laboratory conditions. Common leaf damage scales are the nominal “yes-no damage scale” that only assesses damage incidence, as well as difficult-to-analyse ordinal scales which combine incidence and severity information such as the “Simple 1 to 5 whole plant damage scale”, “Davis’ 0 to 9 whorl & furl damage scale”, or “Williams’ 0 to 9 whole plant damage scale”. These scales have been adapted many times, are sometimes used incorrectly, or were wrongly cited. We therefore propose simplifications of some of these scales as well as a novel “0.0 to 4.0 fall armyworm leaf damage index” which improves precision and possibilities for parametric data analyses. We argue that the choice of a scale to use should depend on the desired level of detail, type of data analyses envisioned, and manageable time investment.

Five field surveys for indigenous entomopathogenic nematodes (EPNs) were conducted in 22 semi-natural and 17 small-holder farming habitats across 16 districts of different altitudes in the northern, eastern, southern and Kigali city provinces of Rwanda. In 2014, 216 mixed soil samples were collected and subsamples thereof baited with Galleria mellonella or Tenebrio molitor larvae. Five samples from five locations and habitats were positive for nematodes (2.8%). Nine nematode species/strains were isolated and five successfully maintained. DNA sequence comparisons and morphological examinations revealed Steinernema carpocapsae, Heterorhabditis bacteriophora, as well as two steinernematids and one heterorhabditid with no species designation. The isolates (strains) were named Steinernema sp. RW14-M-C2a-3, Steinernema sp. RW14-M-C2b-1, Steinernema carpocapsae RW14-G-R3a-2, H. bacteriophora RW14-N-C4a and Heterorhabditis sp. RW14-K-Ca. These are the first records of naturally occurring EPNs in Rwanda. It is also the first record of S. carpocapsae from Africa. Finding H. bacteriophora from tropical rather than temperate Africa was surprising. The found nematodes will serve as the basis for efficacy screening, and for mass production in a biocontrol agent factory at Rubona Research Centre of the Rwanda Agriculture Board with the ultimate aim of delivering effective, safe and environmentally benign pest control for soil-inhabiting pests. ARTICLE HISTORY

Species of the nematode genus Heterorhabditis are important biological control agents against agricultural pests. The taxonomy of this group is still unclear as it currently relies on phylogenetic reconstructions based on a few genetic markers with little resolutive power, specially of closely related species. To fill this knowledge gap, we sequenced several phylogenetically relevant genetic loci and used them to reconstruct phylogenetic trees, to calculate sequence similarity scores, and to determine signatures of species- and population-specific genetic polymorphism. In addition, we revisited the current literature related to the description, synonymisation, and declaration as species inquirendae of Heterorhabditis species to compile taxonomically relevant morphological and morphometric characters, characterized new nematode isolates at the morphological and morphometrical level, and conducted self-crossing and cross-hybridization experiments. The results of this study show that the sequences of the mitochondrial cytochrome C oxidase subunit I (COI) gene provide better phylogenetic resolutive power than the sequences of nuclear rRNA genes and that this gene marker can phylogenetically resolve closely related species and even populations of the same species with high precision. Using this gene marker, we found two new species, Heterorhabditis ruandica n. sp. and Heterorhabditis zacatecana n. sp. A detailed characterization of these species at the morphological and morphometric levels and nematode reproduction assays revealed that the threshold for species delimitation in this genus, using COI sequences, is 97% to 98%. Our study illustrates the importance of rigorous morphological and morphometric characterization and multi-locus sequencing for the description of new species within the genus Heterorhabditis, serves to clarify the phylogenetic relationships of this important group of biological control agents, and can inform future species descriptions to advance our efforts towards developing more tools for sustainable and environmentally friendly agriculture.

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.

White grubs are largely unsolved problems in vegetable and tuber production in East Africa. Novel Rwandan as well as international entomopathogenic nematodes (EPNs) were screened in nine laboratory bioassays and two small-scale field trials in 2014 and 2015. Soil-based laboratory bioassays revealed that all EPNs were able to infect Anomala graueri larvae (Coleoptera: Scarabeidae), although a relatively high number of infective juveniles were needed. Rwandan EPNs were as infectious as their corresponding international strains. At 100 infective juveniles per larva, the Heterorhabditis bacteriophora strains (Rwanda14-N-C4a and international H06) as well as the international Steinernema carpocapsae All caused 18 to 22% grub mortality within 7 days compared to the control. At 1000 infective juveniles, both H. bacteriophora strains as well as the Rwandan S. carpocapsae RW14-G-R3a-2 killed 34 up to 58%. The Rwandan Steinernema RW14-M-C2a-3 least performed in the bioassays (2 to 6%). In two Irish potato fields, the into-soil-applied 1 × 10 9 infective juvenile Steinernema RW14-M-C2b-1 per hectare reduced 29 ± 33% and 96 ± 3% of grubs within 30 and 60 days, respectively. About 1 up to 2.5 × 10 9 infective juvenile Steinernema longicaudum X7 per hectare reduced 77 up to 85% of grubs until day 30, respectively, and 82 up to 95% until day 60. Avermectin + Chlorpyrifos tuber coatings reduced 39% of grubs, and Fipronil + Chlorpyrifos reduced 27%, whereas handpicking did not help much. In conclusion, at least Steinernema RW14-M-C2b-1 and S. longicaudum X7 are promising for managing white grubs in tuber production, this is at a rate of at least 1.5 × 10 9 EPNs per hectare, but H. bacteriophora RW14-N-C4a needs further field research. Findings will support the biocontrol product development in Rwanda, including registration if any would be needed for native macrobial biocontrol agents.