Understanding the factors influencing fall armyworm (Spodoptera frugiperda J.E. Smith) damage in African smallholder maize fields and quantifying its impact on yield: a case study in eastern Zimbabwe

Open Access Article; Published online: 26 Jan 2019Fall armyworm (FAW, Spodoptera frugiperda J.E. Smith) is an invasive lepidopteran pest established in most of sub-Saharan Africa since 2016. Although the immediate reaction of governments has been to invest in chemical pesticides, control methods based on agronomic management would be more affordable to resource-constrained smallholders and minimize risks for health and the environment. However, little is known about the most effective agronomic practices that could control FAW under typical African smallholder conditions. In addition, the impact of FAW damage on yield in Africa has been reported as very large, but these estimates are mainly based on farmers' perceptions, and not on rigorous field scouting methods. Thus, the objectives of this study were to understand the factors influencing FAW damage in African smallholder maize fields and quantify its impact on yield, using two districts of Eastern Zimbabwe as cases. A total of 791 smallholder maize plots were scouted for FAW damage and the head of the corresponding farming household interviewed. Grain yield was later determined in about 20% of these fields. FAW damage was found to be significantly reduced by frequent weeding operations and by minimum- and zero-tillage. Conversely, pumpkin intercropping was found to significantly increase FAW damage. FAW damage was also found to be higher for some maize varieties, although these varieties may not be the lowest yielding. If the incidence of plants with FAW damage symptoms recorded in this research (32–48%, depending on the estimate used) is commensurate with what other studies conducted on the continent found, our best estimate of the impact of FAW damage on yield (11.57%) is much lower than what these studies reported. Although our study presents limitations, losses due to FAW damage in Africa could have been over-estimated. The threat that FAW represents for African smallholders, although very real, should not divert attention away from other pressing challenges they face

Assessment of effectiveness of maize seed treated with cyantraniliprole and thiamethoxam for management of fall armyworm, Spodoptera frugiperda (J. E. Smith)

Open Access ArticleThe effectiveness of maize seed treatments for management of fall armyworm (FAW) (Spodoptera frugiperda) was evaluated under natural infestation conditions in Zambia in 2019, 2020 and 2022. Two seed treatments were tested: cyantraniliprole (Fortenza® 600 FS) + thiamethoxam (Cruiser® 600 FS) (combination marketed as Fortenza® Duo) and Fortenza® 600 FS. Other treatments included each of the two seed treatments supplemented with threshold-based rotational sprays of Denim Fit® 50 WG (emamectin benzoate + lufenuron) and Ampligo® (chlorantraniliprole + lambda cyhalothrin), Denim Fit/Ampligo alone, untreated controls, Ecoterex® 0.5% GR (deltamethrin + pirimiphos methyl) and Mythic® FN SC (chlorantraniliprole). The incidence of FAW-infested plants and plant damage scores were recorded weekly for 4–5 weeks post-emergence. At harvest, grain yield, yield increase over untreated control and cost-benefit ratios were also determined. Although there were some seasonal variations in treatment effectiveness, plots established from Fortenza Duo-treated seed generally had significantly lower plant damage within the first 3–5 weeks of growth. The number of follow-on insecticide sprays were reduced from 2 to 1 in February 2022 plantings in plots established from Fortenza Duo-treated seed. Grain yields were highest in the Denim Fit/Ampligo plots (December 2021 plantings) and Fortenza Duo + Denim Fit/Ampligo plots (December 2021 and February 2022 plantings). In both plantings of the 2021-22 season, mean yield increase over untreated control was highest in Fortenza Duo + Denim Fit/Ampligo plots. Cost-benefit ratios were, however, highest where Fortenza Duo-treated seed was planted without any follow-on chemical sprays and lowest and negative in sole Fortenza plots. Due to method of application and systemic action, Fortenza Duo maize seed treatments may be a perfect fit in FAW integrated pest management (IPM) programs where there is need for judicious pesticide use

Managing a transboundary pest: the fall armyworm on maize in Africa

Published online: 16 Mar 2021The fall armyworm (Spodoptera frugiperda J.E Smith) (Lepidoptera: Noctuidae) invaded Africa in 2016, and has since spread to all countries in sub-Saharan Africa, causing devastating effects on mainly maize and sorghum. The rapid spread of this pest is aided by its high reproductive rate, high migration ability, wide host range and adaptability to different environments, among others. Since its introduction, many governments purchased and distributed pesticides for emergency control, with minimal regard to their efficacy. In this chapter, we review efforts towards managing this pest, highlight key challenges, and provide our thoughts on considerations for sustainable management of the pest

Reproductive Capacities and Development of a Seed Bruchid Beetle, Acanthoscelides macrophthalmus, a Potential Host for the Mass Rearing of the Parasitoid, Dinarmus basalis

The reproductive capacities and development of the seed beetle Acanthoscelides macrophthalmus (Schaeffer) (Coleoptera: Bruchidae), found in Togo, were determined under natural conditions in a Guinean zone for its use as a substitute host for the mass rearing of the parasitoid Dinarmus basalts Rond (Hymenoptera: Pteromalidae), a biological agent for the control of beetles that are pests of cowpea, Vigna unguiculata (L.) Walpers (Fabales: Fabaceae). Population dynamics at the field level; and survival, fecundity and offspring production by A. macrophthalmus under laboratory conditions were measured when fed on its natural plant-host Leucaena leucocephala (Lamark) deWit (Fabales: Mimosaceae). The data resulting from the laboratory study were used to calculate the demographic parameters of A. macrophthalmus by establishing its fertility and life tables. Contrary to cultivated leguminous food plants, L. leucocephala is a perennial sub-spontaneous leguminous plant whose pods are available year round. Although A. macrophthalmus was present in nature throughout the year, its infestation rate of the pods fluctuated according to the phenology of the plant. The maximum infestation of L. leucocephala pods was observed between August and December. Four larval stages and one pupal stage of A. macrophthalmus were identified in the laboratory. The total mean development time varied on average 33.75 ± 2.87 days on the mature pods and 33.39 ± 2.02 days on seeds. The adult female lived from one to two weeks. During its life time, the female laid an average of 62.3 ± 19 and 43.1 ± 13 eggs on the mature pods and seeds respectively and produced an average of 36.7 ± 11.3 offspring on the mature pods and 21.8 ± 8.4 offspring on seeds. On seeds, the net reproduction rate was 5.88 females per female and the intrinsic rate of population increase 0.051 per day. The generation time was 34.59 days and the doubling time 13.59 days. The demographic parameters of A. macrophthalmus in this study are close to those of Callobruchus maculatus F. (Bruchidae), the natural host of D. basalts in a previous study. A. macrophthalmus could therefore be used as substitute host for the mass rearing of D. basalts and subsequently its release in farmers' storage containers. The data presented in this study provide some baseline information regarding the reproductive capacities of A. macrophthalmus that may be useful for its promotion as a substitute host for mass rearing of D. basalts

Sustainable management of fall armyworm, Spodoptera frugiperda (J.E. Smith): challenges and proposed solutions from an African perspective

Published online: 27 Jan 2022Fall armyworm (FAW), Spodoptera frugiperda, is threatening food security in Africa and thus sustainable management strategies are required. The pest has spread to over 44 countries in Africa since its first detection in 2016, causing maize yield losses valued at between US$2,531 and US$6,312 million per annum. Owing to FAW’s damaging potential, many untested management strategies, including those of doubtful efficacy, are being used by smallholder farmers in Africa. We analysed existing and emerging FAW management strategies on the continent. Research and training has focussed on FAW identification, scouting, digital monitoring tools, pest distribution, natural enemy database, and FAW impact on crops. Gaps identified include lack of clear national policies and regulations, FAW identification challenges, absence of reliable and sustainable management options, and FAW insecticide resistance development. Conservation of FAW natural enemies could enhance sustainable natural control. Farmer Field Schools and mass rearing of natural enemies for augmentative release are sustainable FAW control strategies. The “push-pull” strategy in controlling FAW has potential in Africa. Existing policies and regulations to facilitate better FAW management are discussed

Steborer research in Zimbabwe: prospects for the establishment of Cotesia flavipes Cameron

The stemborers Busseola fusca (Fuller) and Chilo partellus (Swinhoe) cause the highest economic damage to maize and sorghum in Zimbabwe. A number of studies on stemborer bioecology and management in Zimbabwe have been conducted, but most are still incomplete. The more important of these are studies on life history, incidence and distribution patterns, host plants, yield losses, chemical control, cultural control, host plant resistance, the use of sex pheromones, and biological control. These are discussed here in detail, and areas where further research is needed are pointed out. As part of an integrated strategy for managing stemborers in Zimbabwe, an exotic braconid larval parasitoid, Cotesia flavipes Cameron, has been released in the lowveld area and prospects for its establishment appear to be good. However, this establishment might be curtailed mainly by the inability of Co. flavipes to adapt to the seasonal carryover mechanisms utilised by the indigenous Cotesia sesamiae (Cameron). RÉSUMÉ Les foreurs Busseola fusca (Fuller) et Chilo partellus (Swinhoe) causent les plus grands dégâts économiques sur maïs et sorgho au Zimbabwe. A certain nombre d'études ont été menées sur la bio-écology et la gestion des foreurs au Zimbabwe, mais plusieurs sont encore inachevées. Les plus importantes d'entre elles sont: l'étude des cycles de vie, l'incidence et le mode de répartition, les plantes hôtes, les pertes de récoltes, la lutte chimique, les pratiques culturales, la résistance des plantes, l'utilisation de phéromones sexuels et la lutte biologique. Ces études sont discutées en détails dans cet article et les aspects nécessitant des études plus approfondies sont soulignées. Dans le cadre d'une strategie intégrée de la gestion des foreurs au Zimbabwe, un parasitoïde larvaire exotique, Cotesia flavipes Cameron, a été lâché dans la région de basse altitude et les possibilities d'acclimation semblent être excellents. Toutefois, cette acclimatation pourrait être limitée par l'inabilité de Co. flavipes à s'adapter aux mechanisms de passages saisoniers, utilisés par le parasitoïde local Cotesia sesamiae (Cameron)

Malaria vector species composition and relative abundance in Mutare and Mutasa districts, Zimbabwe

Regular entomological monitoring is important to determine changes in mosquito species composition and relative densities of malaria vectors in relation to vector control interventions. A study to gain insights into malaria vector species composition and relative abundance was undertaken in Mutare and Mutasa districts, Zimbabwe. Two methods; indoor resting catches and larval sampling were used to collect indoor resting adults and larvae from May 2013 to April 2014. Mosquitoes collected as adults and reared from larvae that were identified morphologically as potential malaria vectors were further processed to sibling species by polymerase chain reaction (PCR). Morphological identification of anopheline mosquitoes showed presence of two complexes: <em>An. funestus</em> and <em>An. gambiae</em>. The total number of female members of the <em>An. funestus</em> group and <em>An. gambiae</em> complex collected by both methods from the two sites was 840 and 31 respectively. Malaria vector species of both complexes were more abundant in Mutare than in Mutasa. The PCR-based assays showed the presence of four sibling species: <em>An. funestus</em> <em>sensu</em> <em>stricto</em> (90.8%, 267/294) and <em>An. leesoni</em> (5.1%, 15/294), of <em>An. funestus</em> group; <em>An. arabiensis</em> (41.9%, 13/31) and <em>An. quadriannulatus</em> (48.4%, 15/31) of the <em>An. gambiae</em> complex. About 4% and 5% of specimens of <em>An. gambiae</em> complex and A<em>n. funestus</em> group respectively did not amplify. Of the two identified malaria vector sibling species, An. funestus sensu stricto was more abundant (95.4%, 267/280) than <em>An. arabiensis</em> (4.6%, 13/280), suggesting the replacement to secondary vector of <em>An. arabiensis</em>, which was previously the predominant vector species. <em>An. funestus</em> <em>sensu</em> <em>stricto</em> and <em>An</em>. <em>arabiensis</em>, the most important vectors of human malaria were identified in this study, but their resting and biting habits as well as insecticide susceptibility are unclear. Further studies on vector behaviour are therefore recommended

Integrated management of Spodoptera frugiperda 6 years post detection in Africa: a review

Published online: 06 May 2022The introduction of fall armyworm (FAW) Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) on the African continent has led to paradigm shifts in pest control in maize systems, occasioned by year-round populations. The discovery of resident parasitoid species adapting to the new pest significantly informed decision-making toward avoiding highly hazardous synthetic insecticides to control the pest. A number of biopesticides have shown promise against the fall armyworm, providing a new arsenal for the sustainable management of this invasive pest. However, a few knowledge gaps remain for a fully integrated and sustainable FAW-management approach, particularly on host-resistance potential