The Fall Armyworm and Larger Grain Borer Pest Invasions in Africa: Drivers, Impacts and Implications for Food Systems.

Invasive alien species (IAS) are a major biosecurity threat affecting globalisation and the international trade of agricultural products and natural ecosystems. In recent decades, for example, field crop and postharvest grain insect pests have independently accounted for a significant decline in food quantity and quality. Nevertheless, how their interaction and cumulative effects along the ever-evolving field production to postharvest continuum contribute towards food insecurity remain scant in the literature. To address this within the context of Africa, we focus on the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), and the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), two of the most important field and postharvest IAS, respectively, that have invaded Africa. Both insect pests have shown high invasion success, managing to establish themselves in >50% of the African continent within a decade post-introduction. The successive and summative nature of field and postharvest damage by invasive insect pests on the same crop along its value chain results in exacerbated food losses. This systematic review assesses the drivers, impacts and management of the fall armyworm and larger grain borer and their effects on food systems in Africa. Interrogating these issues is important in early warning systems, holistic management of IAS, maintenance of integral food systems in Africa and the development of effective management strategies.

Comparative utility of hermetic and conventional grain storage bags for smallholder farmers: a meta-analysis.

Postharvest management is critical to attaining household food, nutrition, and income security. Hermetic grain storage bags offer an effective pesticide-free way to protect stored grain against fungal and insect infestation. We evaluated articles indexed in the Web of Science that included experiments comparing the storage efficacy of conventional and hermetic storage bags based on grain germination rate, insect infestation, physical damage, mycotoxin contamination, and changes in weight and moisture content. Compared with grain stored in hermetic bags, grain stored in conventional bags lost 3.6-fold more seed viability, contained 42-fold more insects, had 11-fold more physical damage, and lost 23-fold more grain weight, while grain moisture levels were similar for both hermetic and conventional storage bags. Mycotoxin contamination levels were not as frequently assessed. Levels could be low in grain stored in both types of bags, or levels could be low in hermetic bags and significantly higher in conventional bags. The improved properties of grain stored in hermetic bags can increase food security and household income by providing safe storage options for maintaining seed germinability, and for consumption and/or sale when food supplies are high, or when prices are low. Hermetic bags are economically feasible for use by subsistence farmers in Sub-Saharan Africa for grain for household consumption and for carrying-over seed for planting in the next season. Additional studies are needed to verify the mycotoxin contamination results and to determine if there are differences in functional food characteristics, e.g. flavor and cooking properties, that have not been as comprehensively studied. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Abstracts of Presentations to the Working Session on Improving Predictive Modeling of Mycotoxin Risk for Africa Held at the 3rd ASM2022 on 7 September 2022, in Stellenbosch, South Africa.

In 2008, the African Postharvest Losses Information Systems project (APHLIS, accessed on 6 September 2022) developed an algorithm for estimating the scale of cereal postharvest losses (PHLs). The relevant scientific literature and contextual information was used to build profiles of the PHLs occurring along the value chains of nine cereal crops by country and province for 37 sub-Saharan African countries. The APHLIS provides estimates of PHL figures where direct measurements are not available. A pilot project was subsequently initiated to explore the possibility of supplementing these loss estimates with information on the aflatoxin risk. Using satellite data on drought and rainfall, a time series of agro-climatic aflatoxin risk warning maps for maize was developed covering the countries and provinces of sub-Saharan Africa. The agro-climatic risk warning maps for specific countries were shared with mycotoxin experts from those countries for review and comparison with their aflatoxin incidence datasets. The present Work Session was a unique opportunity for African food safety mycotoxins experts, as well as other international experts, to meet and deepen the discussion about prospects for using their experience and their data to validate and improve agro-climatic risk modeling approaches.

Sub-optimal host plants have developmental and thermal fitness costs to the invasive fall armyworm.

The fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) is a global invasive pest of cereals. Although this pest uses maize and sorghum as its main hosts, it is associated with a wide range of host plants due to its polyphagous nature. Despite the FAW's polyphagy being widely reported in literature, few studies have investigated the effects of the non-preferred conditions or forms (e.g., drought-stressed forms) of this pest's hosts on its physiological and ecological fitness. Thus, the interactive effects of biotic and abiotic stresses on FAW fitness costs or benefits have not been specifically investigated. We therefore assessed the effects of host plant quality on the developmental rates and thermal tolerance of the FAW. Specifically, we reared FAW neonates on three hosts (maize, cowpeas, and pearl millet) under two treatments per host plant [unstressed (well watered) and stressed (water deprived)] until the adult stage. Larval growth rates and pupal weights were determined. Thermal tolerance traits viz critical thermal maxima (CTmax), critical thermal minima (CTmin), heat knockdown time (HKDT), chill-coma recovery time (CCRT), and supercooling points (SCPs) were measured for the emerging adults from each treatment. The results showed that suboptimal diets significantly prolonged the developmental time of FAW larvae and reduced their growth rates and ultimate body weights, but did not impair their full development. Suboptimal diets (comprising non-cereal plants and drought-stressed cereal plants) increased the number of larval instars to eight compared to six for optimal natural diets (unstressed maize and pearl millet). Apart from direct effects, in all cases, suboptimal diets significantly reduced the heat tolerance of FAWs, but their effect on cold tolerance was recorded only in select cases (e.g., SCP). These results suggest host plant effects on the physical and thermal fitness of FAW, indicating a considerable degree of resilience against multiple stressors. This pest's resilience can present major drawbacks to its cultural management using suboptimal hosts (in crop rotations or intercrops) through its ability to survive on most host plants despite their water stress condition and gains in thermal fitness. The fate of FAW population persistence under multivariate environmental stresses is therefore not entirely subject to prior environmental host plant history or quality.

Field evaluation of hermetic and synthetic pesticide-based technologies in smallholder sorghum grain storage in hot and arid climates.

Field evaluation of six grain storage technologies under hot and arid conditions (32-42 °C; rainfall < 450 mm/year) in two locations in Zimbabwe were conducted over two storage seasons. The treatments included three hermetic technologies (Purdue Improved Crop Storage bags, GrainPro Super Grainbags, metal silos); three synthetic pesticide-based treatments; and an untreated control, all using threshed sorghum grain. Sampling was at eight-week intervals for 32 weeks. Highly significant differences (p < 0.01) occurred between hermetic and non-hermetic treatments regarding grain damage, weight loss, insect pest populations, and grain moisture content; with the hermetic containers exhibiting superior grain protection. Weight losses were low (< 3%) in hermetic treatments compared to pesticide-based treatments (3.7 to 14.2%). Tribolium castaneum developed in metal silos, deltamethrin-incorporated polypropylene bags and a pesticide treatment containing deltamethrin 0.13% and fenitrothion 1% while Sitotroga cerealella developed in a pesticide treatment containing pirimiphos-methyl 0.16% + thiamethoxam 0.036%. Mechanisms of survival and development of these pests in the tested treatments and under similar climatic conditions need further elucidation. These hermetic technologies can be successfully used by smallholder farmers in developing countries as alternatives to synthetic pesticides for protecting stored-sorghum grain under hot and arid climatic conditions to attain household food security. To our knowledge, this is the first published study on modern hermetic storage of sorghum grain under typical smallholder storage conditions and involving stakeholders.

Addition of a surfactant to water increases the acaricidal activity of extracts of some plant species used to control ticks by Zimbabwean smallholder farmers.

BACKGROUND: Many studies have revealed that bioactive compounds for different indications are not extracted from plants with water, the only extractant practically available to rural communities. We compared the acaricidal activity of acetone extracts of 13 species used traditionally to protect cattle against ticks. We also investigated if the extraction of biologically active compounds against Rhipicephalus (Boophilus) decoloratus ticks could be enhanced by adding a liquid soap that is locally available to smallholder farmers. METHODS: A total of 13 plant species selected based on reported traditional use in Zimbabwe, were dried and finely ground before extraction with water, or water plus a surfactant, or acetone. The adapted Shaw Larval Immersion Test (SLIT) method was used to determine the activity of acetone and crude water extracts with or without liquid soap against the tick larvae. The activity of four fractions of crude acetone extracts (extracted using solvents of different polarity), of the most active plant species, Maerua edulis (tuber and leaf) was also compared to identify the most active fraction. RESULTS: Aqueous plant extracts were not toxic to ticks, but the addition of 1% liquid soap as a surfactant increased mortality of the R. (B) decoloratus larvae significantly. With the Maerua edulis tuber extract, the efficacy of the 1% liquid soap was comparable to that of the amitraz based commercial synthetic acaricide. The use of acetone as an extractant, also increased the mortality of the tick larvae in all the plant species. With M. edulis (tuber and leaf), Monadenium lugardae and Kleinia sp. acetone extracts, the activity was comparable to that of the positive control (a commercially available amitraz-based synthetic acaricide). The non-polar fractions of the acetone extract of leaf and tuber of M. edulis caused up to 100% mortality. This indicates that non-polar to intermediate polarity compounds are responsible for the acaricidal activity. CONCLUSION: Organic solvents such as acetone extracted active compounds but water did not. By adding commonly available dishwashing soap to water active compounds were extracted leading to a high acaricidal activity of the plant extracts. In some cases, it was as active as non-polar extracts and a synthetic commercial acaricide (positive control). This approach makes it possible for the smallholder farmers and traditional healers to extract biologically active compounds from plants by using water.

Novel Agmatine Derivatives in Maerua edulis With Bioactivity Against Callosobruchus maculatus, a Cosmopolitan Storage Insect Pest.

Food security in developing countries is threatened by crop pests and ectoparasites in livestock. Strategies for their management still rely on synthetic pesticides which are not always effective and the active ingredients persist in the environment with negative consequences for beneficial arthropods, farmers and consumers, hence necessitating research on sustainable alternatives. Botanical insecticides are increasingly relevant, typically having lower impacts on users, consumers and the environment. One example is the southern African shrub the Blue bush-berry, Maerua edulis. Recent work reported effective pest control using this plant species against cattle ticks, storage beetles and vegetable pests. However, little is known about the chemistry underlying activity and this is essential to optimize its use. Here, we identified two novel plant chemical structures, the E and Z isomers of cinnamoyl-4-aminobutylguanidine along with the E and Z isomers of 4-hydroxycinnamoyl-4-aminobutylguanidine in the leaves of M. edulis. We isolated these compounds from the leaves and elucidated their chemical structures using various spectroscopic techniques including High Resolution Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy. We also identified a further 11 closely related structures of which 6 are tentatively reported here for the first time. Stachydrine and 3-hydroxystachydrine were also identified in the leaf extract, and occurred at very high concentrations; up to 2% w/w of dry leaves. We tested these two compounds, along with the 4 main cinnamoylamides and the crude M. edulis leaf extract against the cowpea bruchid Callosobruchus maculatus at concentrations equivalent to those present in extracts used by smallholder farmers. Mortality of insects exposed to crude plant extracts after 72 h was significantly higher than the untreated control although still lower than for insects exposed to rotenone, the positive control. The two new compounds and stachydrine showed similar activity to the crude extracts suggesting that these compounds explained the activity of the extract. After 6 days, the mortality of insects exposed to crude extracts and isolated compounds was similar to that recorded with the positive control. The stachydrine fraction and the E and Z isomers of cinnamoyl-4-aminobutylguanidine also inhibited oviposition activity in fecund female beetles. Our data show that methanol extracts of M. edulis were toxic to C. maculatus and inhibited oviposition even at 0.1% w/v so these foliar chemicals may explain the activity of the plant material. We also synthesized the amides which facilitated structural elucidation, produced adequate quantities for testing and demonstrated the potential for commercial synthesis.

Natural postharvest aflatoxin occurrence in food legumes in the smallholder farming sector of Zimbabwe.

Aflatoxins, mainly produced by Aspergillus flavus and Aspergillus parasiticus, are highly toxic and may lead to health problems such as liver cancer. Exposure to aflatoxins may result from ingestion of contaminated foods. Levels of AFB1, AFB2, AFG1 and AFG2 in samples of groundnuts (Arachis hypogaea), beans (Phaseolus vulgaris), cowpeas (Vigna unguiculata) and bambara nuts (Vigna subterranean) grown by smallholder farmers in Shamva and Makoni districts, Zimbabwe, were determined at harvesting, using high performance liquid chromatography after immunoaffinity clean-up. Aflatoxins were detected in 12.5% of groundnut samples with concentrations ranging up to 175.9 µg/kg. Aflatoxins were present in 4.3% of the cowpea samples with concentrations ranging from 1.4 to 103.4 µg/kg. Due to alarming levels of aflatoxins detected in legumes versus maximum permissible levels, there is a need to assist smallholder farmers to develop harvest control strategies to reduce contamination of aflatoxins in legumes.

Acute Oral Mammalian Toxicity and Effect of Solvents on Efficacy of Maerua edulis (Gilg. & Ben.) De Wolf against Rhipicephalus (Boophilus) decoloratus Koch, 1844 (Acarina: Ixodidae), Tick Larvae.

Efficacy and toxicity of aqueous and organic solvents extracts of Maerua edulis against ticks and mice, respectively, were determined. Ground leaves were extracted separately using cold water, cold water plus surfactant (1% v/v liquid soap), hot water plus surfactant, hexane, or methanol to make 25% w/v stock solutions from which serial dilutions of 5, 10, 20, and 25% were made. For each concentration, 20 Rhipicephalus decoloratus tick larvae were put in filter papers impregnated with extracts and incubated for 48 h at 27°C and 85-90% RH for mortality observation after 24 h and 48 h. In the toxicity experiment, hot water plus surfactant treatments of 5, 10, 20, and 25% (w/v) M. edulis were administered in suspension per os to sexually mature Balb/C mice and observed for clinical signs and mortality for 72 h. Larvae mortality was highest (>98%) in methanol-extracted M. edulis treatments (20 and 25%), which was not different from the amitraz-based control (Tickbuster®). Mortality was also higher in the hot water than in cold water plus surfactant treatments (P < 0.05). No postadministration adverse health effects were observed in the mice. These results suggest that M. edulis is an effective tick remedy best extracted using methanol or hot water plus surfactant.

Ethnoveterinary plants and practices used for ecto-parasite control in semi-arid smallholder farming areas of Zimbabwe.

BACKGROUND: The inclusion of traditional plant-based ecto-parasite control methods in primary health care of livestock is increasingly becoming an important intervention for improving livestock productivity in resource-challenged smallholder farming areas. In this study, commonly used plants used for the control of cattle ticks and other pests were identified through a survey in four semi-arid districts of Zimbabwe. METHODS: A standard structured questionnaire with details of demographics, socioeconomic status of households, livestock parasites, control practices and list of ethnoveterinary plants used was used to interview 233 knowledgeable smallholder farmers in four districts. Focus group discussions with community members further provided insights on how the plants were being used and other issues surrounding ecto-parasite control and indigenous knowledge systems in the study areas. RESULTS: The older generation (>40 years) of the respondents were knowledgeable about ethnoveterinary plants and practices. Overall, 51 plant species were reportedly effective against cattle ticks and other livestock parasites. The most frequently mentioned plants were in descending order, Cissus quadrangularis (30.1%), Lippia javanica (19.6%), Psydrax livida (14.9%) and Aloe sp (14.9%). Most of the plant materials were prepared by crushing and soaking in water and spraying the extract on animals. Despite the knowledge of these useful pesticidal plants, the preferred animal health care for cattle and other highly ranked livestock species is still the use of commercial acaricides. Cattle dipping services were reported sporadic by 48% of the respondents. Traditional knowledge and plants are considered only as an alternative in the absence of conventional synthetic products. CONCLUSIONS: Livestock farming communities know of plant species used for livestock ecto-parasite control. The plant species are mostly used to complement commercial products. More work, is required to confirm the acaricidal properties claimed by the farmers in order to optimize and promote sustainable use of these plants.

Efficacy of Strychnos spinosa (Lam.) and Solanum incanum L. aqueous fruit extracts against cattle ticks.

The efficacy of Solanum incanum and Strychnos spinosa aqueous fruit extracts was evaluated against cattle ticks in on-station experiments and laboratory tick bioassays. In the on-station experiment using cattle, fruit extracts were applied at three concentrations 5, 10, and 20 % (w/v) and compared with a commercial acaricide, Tickbuster (amitraz) spray (positive control) and no treatment (negative control). The treatments were applied at weekly intervals for 6 weeks as surface sprays on 32 Mashona cattle in a completely randomized design experiment. Ticks on individual cattle were identified, counted, and recorded daily. Peripheral blood samples were collected for parasite screening. In the laboratory, tick bioassays were conducted at four concentrations, 5, 10, 20, and 40% (w/v) fruit extracts compared to Tickbuster (amitraz) spray (positive control) and distilled water (negative control). The extracts were incubated with Rhipicephalus (Boophilus) decoloratus tick larvae and mortalities for each treatment level recorded after 24 and 48 h. The 5% Solanum incanum treatment had higher efficacy ratio (P < 0.05) than the other fruit extract concentrations of the same plant species. Efficacy ratio was higher (P < 0.05) in the 5% S. spinosa-treated cattle than in the untreated control but lower (P < 0.05) than that for the amitraz treatment. The bioassays indicated that there was a high efficacy ratio for the lowest fruit extract concentrations when ticks were exposed to acaricidal treatments for 48 h compared to 24 h. Overall, the results indicate that Solanum incanum and Strychnos spinosa individually have some acaricidal effect.

Acaricidal efficacy against cattle ticks and acute oral toxicity of Lippia javanica (Burm F.) Spreng.

In search for low-cost, safe and environmentally benign plant-based alternatives to commercial pesticides, the efficacy of Lippia javanica aqueous leaf extracts in controlling ticks on cattle, acute oral toxicity in mice and phytochemistry were evaluated. L. javanica aqueous leaf extracts at 10% and 20% w/v were effective at controlling cattle ticks but not as good as an amitraz-based acaricide Tickbuster. However, they can provide an effective tick control option where synthetic products are unavailable or unaffordable, particularly in remote parts of southern Africa. Peripheral blood samples collected showed no haemoparasites in treated cattle implying that animals did not suffer from clinical tick-borne diseases. The leaf aqueous extracts of L. javanica were tested for toxicity in BALB/c mice. While anecdotal evidence suggests L. javanica has low mammalian toxicity, within 48 h all mice fed with the L. javanica leaf aqueous extract at 12.5-37.5% v/v were lethargic, and overall mortality was 37.5% (n = 24). Thus, despite their apparent safety, water extracts of L. javanica leaves may have deleterious health implications on humans and animals if consumed at very high doses. Many compounds have been identified from L. javanica including an array of phenolic glycosides, flavonoids and essential oils but none of these are known to have acute toxic properties.