On-farm storage loss estimates of maize in Kenya using community survey methods.

Maize is the most important staple in sub-Saharan Africa (SSA), with highly seasonal production. High storage losses affect food security, but good estimations are lacking. A new method using focus group discussions (FGDs) was tested with 121 communities (1439 farmers, 52% women) in Kenya's six maize-growing zones, to estimate the maize losses to storage pests and analyze farmer practices. As control strategies, half of the farmers used chemical pesticides (49%), while hermetic bags (16%) and botanicals (15%) were also popular. Relative loss from weevils in the long rains was estimated at 23%, in the short rains 18%, and annually 21%. Fewer farmers were affected by the larger grain borer (LGB) than by maize weevils: 42% in the long rainy season and 32% in the short rainy season; losses from LGB were also smaller: 19% in the long season, 17% in the short season, and 18% over the year. Total storage loss, from both species combined, was estimated at 36%, or 671,000 tonnes per year. The greatest losses occur in the humid areas, especially the moist mid-altitudes (56%), and with smaller loss in the drylands (20-23%). Extrapolating the point data and overlaying with the maize production map shows the geographic distribution of the losses, with the most important area found around Lake Victoria. FGDs provide convenient and cheap tools to estimate storage losses in representative communities, but a total loss estimate of 36% is higher than is found in other studies, so its accuracy and framing effects need to be assessed. We conclude that storage pests remain a major problem, especially in western Kenya, and that the use of environmentally friendly technologies such as hermetic storage and botanicals needs more attention, both by the public extension service and private agrodealers.

Genetic analyses of tropical maize lines under artificial infestation of fall armyworm and foliar diseases under optimum conditions.

Development and deployment of high-yielding maize varieties with native resistance to Fall armyworm (FAW), turcicum leaf blight (TLB), and gray leaf spot (GLS) infestation is critical for addressing the food insecurity in sub-Saharan Africa. The objectives of this study were to determine the inheritance of resistance for FAW, identity hybrids which in addition to FAW resistance, also show resistance to TLB and GLS, and investigate the usefulness of models based on general combining ability (GCA) and SNP markers in predicting the performance of new untested hybrids. Half-diallel mating scheme was used to generate 105 F1 hybrids from 15 parents and another 55 F1 hybrids from 11 parents. These were evaluated in two experiments, each with commercial checks in multiple locations under FAW artificial infestation and optimum management in Kenya. Under artificial FAW infestation, significant mean squares among hybrids and hybrids x environment were observed for most traits in both experiments, including at least one of the three assessments carried out for foliar damage caused by FAW. Interaction of GCA x environment and specific combining ability (SCA) x environment interactions were significant for all traits under FAW infestation and optimal conditions. Moderate to high heritability estimates were observed for GY under both management conditions. Correlation between GY and two of the three scorings (one and three weeks after infestation) for foliar damage caused by FAW were negative (-0.27 and -0.38) and significant. Positive and significant correlation (0.84) was observed between FAW-inflicted ear damage and the percentage of rotten ears. We identified many superior-performing hybrids compared to the best commercial checks for both GY and FAW resistance associated traits. Inbred lines CML312, CML567, CML488, DTPYC9-F46-1-2-1-2, CKDHL164288, CKDHL166062, and CLRCY039 had significant and positive GCA for GY (positive) and FAW resistance-associated traits (negative). CML567 was a parent in four of the top ten hybrids under optimum and FAW conditions. Both additive and non-additive gene action were important in the inheritance of FAW resistance. Both GCA and marker-based models showed high correlation with field performance, but marker-based models exhibited considerably higher correlation. The best performing hybrids identified in this study could be used as potential single cross testers in the development of three-way FAW resistance hybrids. Overall, our results provide insights that help breeders to design effective breeding strategies to develop FAW resistant hybrids that are high yielding under FAW and optimum conditions.

Performance of Bt maize event MON810 in controlling maize stem borers Chilo partellus and Busseola fusca in Uganda.

Stem borers are major insect pests of maize in Uganda. A study was conducted in 2014-2016 to assess the performance of Bt hybrids expressing Cry1Ab (event MON810) against the two major stem borer species in Uganda - the African stem borer (Busseola fusca) and the spotted stem borer (Chilo partellus) - under artificial infestation. The study comprised 14 non-commercialized hybrids, including seven pairs of Bt and non-Bt hybrids (isolines), three non-Bt commercial hybrids and a conventional stem borer resistant check. All stem borer damage parameters (leaf damage, number of internodes tunneled and tunnel length) were generally significantly lower in Bt hybrids than in their isolines, the conventionally resistant hybrid, and local commercial hybrids. Mean yields were significantly higher by 29.4-80.5% in the Bt hybrids than in the other three categories of non-Bt hybrids. This study demonstrated that Bt maize expressing Cry1Ab protects against leaf damage and can limit entry of stem borers into the stems of maize plants, resulting in higher yield than in the non-transgenic hybrids. Thus, Bt maize has potential to contribute to the overall management package of stem borers in Uganda.

Host plant resistance for fall armyworm management in maize: relevance, status and prospects in Africa and Asia.

KEY MESSAGE: Sustainable control of fall armyworm (FAW) requires implementation of effective integrated pest management (IPM) strategies, with host plant resistance as a key component. Significant opportunities exist for developing and deploying elite maize cultivars with native genetic resistance and/or transgenic resistance for FAW control in both Africa and Asia. The fall armyworm [Spodoptera frugiperda (J.E. Smith); FAW] has emerged as a serious pest since 2016 in Africa, and since 2018 in Asia, affecting the food security and livelihoods of millions of smallholder farmers, especially those growing maize. Sustainable control of FAW requires implementation of integrated pest management strategies, in which host plant resistance is one of the key components. Significant strides have been made in breeding elite maize lines and hybrids with native genetic resistance to FAW in Africa, based on the strong foundation of insect-resistant tropical germplasm developed at the International Maize and Wheat Improvement Center, Mexico. These efforts are further intensified to develop and deploy elite maize cultivars with native FAW tolerance/resistance and farmer-preferred traits suitable for diverse agro-ecologies in Africa and Asia. Independently, genetically modified Bt maize with resistance to FAW is already commercialized in South Africa, and in a few countries in Asia (Philippines and Vietnam), while efforts are being made to commercialize Bt maize events in additional countries in both Africa and Asia. In countries where Bt maize is commercialized, it is important to implement a robust insect resistance management strategy. Combinations of native genetic resistance and Bt maize also need to be explored as a path to more effective and sustainable host plant resistance options. We also highlight the critical gaps and priorities for host plant resistance research and development in maize, particularly in the context of sustainable FAW management in Africa and Asia.

Reproductive potential of fall armyworm Spodoptera frugiperda (J.E. Smith) and effects of feeding on diverse maize genotypes under artificial infestation.

Fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) has become a major threat to maize production in Africa. In this study, six maize genotypes were assessed for their resistance to FAW under artificial infestation in both laboratory and net house conditions. These included two FAW-tolerant hybrids (CKHFAW180294 and CKH191221), two commercial hybrids (WE2115 and CKH10717), and two open-pollinated varieties (ZM523 and KDV4). Larval development time and reproductive potential were assessed on maize leaves in the laboratory and a life table for FAW was constructed. The maize genotypes were also artificially infested with three FAW neonates at two phenological stages (V5 and V7) and reproductive stage (R1) in the net house. Leaf and ear damage scores were recorded on a scale of 1-9. Larval development time varied significantly between maize genotypes with the highest on CKH191221 (16.4 days) and the lowest on KDV4 (13.7 days). The intrinsic rate of natural increase for life tables varied from 0.24 on CKH191221 to 0.41 on KDV4. Mean generation time of FAW ranged from 17.6 to 22.8 days on KDV4 and CKH191221, respectively. Foliar damage was the lowest on CKH191221, and the highest on KDV4 at V7 infestation stage in week 1. CKH191221 had the lowest ear damage score, whereas ZM523 had the highest scores at V5 infestation stage. The highest and lowest yield reductions were observed on ZM523 (64%) at V7 infestation stage and CKHFAW180294 (6%) at R1 infestation stage, respectively. The results indicated the potential for developing tropical mid-altitude maize germplasm with native genetic resistance to FAW.

Global Habitat Suitability of Spodoptera frugiperda (JE Smith) (Lepidoptera, Noctuidae): Key Parasitoids Considered for Its Biological Control.

The present study is the first modeling effort at a global scale to predict habitat suitability of fall armyworm (FAW), Spodoptera frugiperda and its key parasitoids, namely Chelonus insularis, Cotesia marginiventris,Eiphosoma laphygmae,Telenomus remus and Trichogramma pretiosum, to be considered for biological control. An adjusted procedure of a machine-learning algorithm, the maximum entropy (Maxent), was applied for the modeling experiments. Model predictions showed particularly high establishment potential of the five hymenopteran parasitoids in areas that are heavily affected by FAW (like the coastal belt of West Africa from Côte d'Ivoire (Ivory Coast) to Nigeria, the Congo basin to Eastern Africa, Eastern, Southern and Southeastern Asia and some portions of Eastern Australia) and those of potential invasion risks (western & southern Europe). These habitats can be priority sites for scaling FAW biocontrol efforts. In the context of global warming and the event of accidental FAW introduction, warmer parts of Europe are at high risk. The effect of winter on the survival and life cycle of the pest in Europe and other temperate regions of the world are discussed in this paper. Overall, the models provide pioneering information to guide decision making for biological-based medium and long-term management of FAW across the globe.

A system dynamics model for pests and natural enemies interactions.

Stemborers (Busseola fusca, Sesamia calamistis and Chilo partellus), the fall armyworm (Spodoptera frugiperda) and associated parasitoids constitute an interacting system in maize fields in Kenya. This work aims at developing and evaluating models that represent the evolution of those interactions by applying system thinking and system dynamics approaches with its archetypes [causal loop diagram (CLD), reinforcing (R) and balancing (B)] to analyse the population of these multi-species systems. The software Vensim PLE 8.0.9 was used to implement the models and carry out the simulations of single- and multi-species systems. The results showed that when a single pest species with its associated parasitoids interact with the host plant, the species was able to establish and sustain by cyclical relationship between populations of the pest and the associated parasitoids. However, in multi- pest species systems, dominance of S. frugiperda and C. partellus over B. fusca and S. calamistis was observed, but without extinction. However, there was a likelihood for B. fusca being displaced by C. partellus. Overall, the models predict the co-existence of fall armyworm with stemborer species as an additional pest of maize in Africa that need to be considered henceforth in designing IPM strategies in maize.

Using Panel Community Surveys to Track the Impact of Crop Pests Over Time and Space - The Case of Maize Lethal Necrosis (MLN) Disease in Kenya from 2013 to 2018.

Maize lethal necrosis (MLN) disease appeared in Kenya in 2011, causing major damage. In a first survey of 121 communities in 2013, participants estimated the proportion of households affected and the yield loss in affected areas; from this survey, the overall loss was estimated at 22%, concentrated in western Kenya (94%). Efforts to combat the disease included planting resistant varieties, creating awareness of MLN management, and producing pathogen-free seed. In 2018, the same communities were revisited and asked the same questions, establishing a panel community survey. The results showed that incidents of MLN had greatly decreased, and the number of communities that had observed it had reduced from 76% in 2013 to 26% by the long rains of 2018; while still common in western Kenya (60%), MLN had greatly reduced elsewhere (to 10%). In 2013, 40% of farmers were affected, yield loss among affected farmers was estimated at 44%, and total yield loss was estimated at 22% (a production loss of 0.5 million metric tons/year), valued at US$187 million. By the long rains of 2018, 23% of farmers were affected, with a loss among affected farmers of 36%; overall annual loss was estimated at 8.5% or 0.37 million metric tons, valued at US$109 million, concentrated in western Kenya (79%). Of the recommended control measures, only the removal of diseased plants was commonly used (by 62% of affected communities), but not the use of agronomic practices (11%) or resistant varieties (9.5%). The reasons for the reduction in MLN are not well understood; external factors such as spraying insecticide against fall armyworm and unfavorable weather likely played a role, as did using disease-free seed, but not the use of resistant varieties or appropriate management practices. Still, as the pathogen remains in the fields, it is important to keep disseminating these control methods, particularly resistant varieties.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Spread and impact of fall armyworm (Spodoptera frugiperda J.E. Smith) in maize production areas of Kenya.

Fall armyworm (FAW), one of the most important pests of maize in Latin America, suddenly appeared in Africa in 2016 and spread rapidly. Estimates of crop losses due to FAW are essential in order to compare the impact of these losses with the cost of controlling FAW and advise appropriate technology dissemination and policy. In this study, therefore, crop losses due to FAW in 2017 and 2018 were estimated in all the maize production areas of Kenya. Data were collected during June and July 2018 through 121 group discussions with 1439 farmers, separately with men (697) and women (742), in communities that were randomly selected to represent the major maize growing areas. The results showed that most participants (82%) could correctly identify the FAW from pictures. By 2016, FAW was observed by more than half of the communities (53%), with most of the other half first observing FAW in 2017. The proportion of farmers affected by FAW substantially increased, from the long rains of 2017 (63%) to the long rains of 2018 (83%), and in all zones except for the high tropics and moist mid-altitudes. However, the percentage of loss experienced by affected farmers decreased slightly, from 54% in 2017 to 42% in 2018. In 2017, the low- and medium-potential maize-production areas were the most affected, with losses of >50%, with high-potential areas facing losses of about 30%, resulting in a total loss of 37% for the whole country. In the main 2018 season, losses in the low- and medium-potential areas were less - about 20%, but the high-potential areas were now more affected, leading to a total estimate of 33%. We conclude that FAW has suddenly become a major pest in Kenya, causing losses of about a third of the annual maize production, estimated at about 1 million tonnes.

Identification and diversity of tropical maize inbred lines with resistance to common rust (Puccinia sorghi Schwein).

Common rust (CR) caused by Puccinia sorghi Schwein is one of the major foliar diseases of maize (Zea mays L.) in Eastern and Southern Africa. This study was conducted to (i) evaluate the response of elite tropical adapted maize inbred lines to Puccinia sorghi and identify resistant lines (ii) examine associations between CR disease parameters and agronomic traits, and (iii) assess the genetic diversity of the inbred lines. Fifty inbred lines were evaluated in field trials for three seasons (2017-2019) in Uganda under artificial inoculation. Disease severity was rated on a 1-9 scale at 21 (Rust 1), 28 (Rust 2), and 35 (Rust 3) days after inoculation. Area under disease progress curve (AUDPC) was calculated. The genetic diversity of the lines was assessed using 44,975 single nucleotide polymorphism markers. Combined ANOVA across seasons showed significant (P < .001) line mean squares for the three rust scores and AUDPC. Heritability was high for Rust 2 (0.90), Rust 3 (0.83), and AUDPC (0.93). Of the 50 lines, 12 were highly resistant to CR. Inbred lines CKL1522, CKL05010, and CKL05017 had significantly lower Rust 3 scores and AUDPC compared to the resistant check CML444 and are potential donors of CR resistance alleles. The genetic correlations between CR disease resistance parameters were positive and strong. A neighbor-joining (NJ) tree and STRUCTURE suggested the presence of three major groups among the lines, with lines highly resistant to CR spread across the three groups. The genetic diversity among the highly resistant lines can be exploited by recycling genetically distant lines to develop new multiple disease resistant inbred lines for hybrid development and deployment.

On-Farm Evaluation of Hermetic Technology Against Maize Storage Pests in Kenya.

On-farm trial with a total of 32 farmers in eight villages of Naivasha and Nakuru areas of Kenya was conducted between December 2013 and September 2014 to evaluate hermetic grain storage technologies under farmers' management conditions. The storage technologies evaluated were metal silo and SuperGrain IV-R bag alongside the standard woven polypropylene bag with or without Actellic super dust. Moisture content, insect population, grain discoloration, and weight loss were analyzed 90, 180, and 270 d after storage. Grain moisture content remained stable over the storage period. Both metal silo and SuperGrain IV-R bag suppressed insect population, prevented grain loss and cross-infestation of insects from the surrounding environment. On the contrary, polypropylene bags allowed rapid build up of insect population and re-infestation from the surrounding environment. Grain weight losses were 1.5% in the metal silo and 1.8% in the SuperGrain IV-R bags compared to 32% in the polypropylene bags without Actellic Super dust, 270 d after storage. The present study, therefore, demonstrates that storing grains either in metal silo or SuperGrain IV-R bags would benefit farmers in reducing grain losses and improving quality. The study was of great interest to the farmers, grain storage scientists, and food security experts.

Host acceptance, suitability, and effects of host deprivation on the West African egg parasitoid Telenomus isis (Hymenoptera: Scelionidae) reared on East African stemborers under varying temperature and relative humidity regimens.

Scelionid egg parasitoids of Telenomus spp. have been shown to significantly affect noctuid stemborer populations and yields of maize in western Africa. One of them, T. isis, has never been reported from eastern Africa and was introduced into the laboratories of the International Centre of Insect Physiology and Ecology, Kenya. This study evaluates the biotic potential of T. isis using East African stemborers as hosts. Host acceptance was tested using 15 lepidopteran borer species. Only noctuid stemborers were accepted for oviposition by T. isis. Sesamia calamistis Hampson, Sesamia nonagrioides (Lefebvre), and Busseola fusca (Fuller) were further used to study the effect of host species, host age, duration of host deprivation, temperature, and humidity on the performance of the parasitoid. In contrast to sex ratio, developmental time, parasitism, and parasitoid emergence varied significantly with host species, and the former two decreased with the age of host eggs. Female longevity increased with duration of host deprivation, whereas average lifetime fecundity decreased, probably because of oocyte resorption. T. isis successfully developed between 18 and 32 degrees C at both low (40-50%) and high (70-80%) relative humidity regimens, but temperature played a more critical role. Using the modified Logan model, the lower and upper temperature thresholds for development were estimated at 11.5 and 37.5 degrees C, respectively, with an optimum at 30.5 degrees C for both humidity regimens. Depending on temperature and relative humidity regimen, the intrinsic rate of increase (r(m)) varied from 0.077 to 0.300, net reproductive rate (R(o)) from 7.70 to 83.96, and generation time (G) from 11 to 38 d. The results of this study indicate that T. isis is likely to establish in eastern Africa.