Influence of inoculated gut bacteria on the development of Bactrocera dorsalis and on its susceptibility to the entomopathogenic fungus, Metarhizium anisopliae.

BACKGROUND: Symbiotic interactions between insects and bacteria have been associated with a vast variety of physiological, ecological and evolutionary consequences for the host. A wide range of bacterial communities have been found in association with the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), an important pest of cultivated fruit in most regions of the world. We evaluated the diversity of gut bacteria in B. dorsalis specimens from several populations in Kenya and investigated the roles of individual bacterial isolates in the development of axenic (germ-free) B. dorsalis fly lines and their responses to the entomopathogenic fungus, Metarhizium anisopliae. RESULTS: We sequenced 16S rRNA to evaluate microbiomes and coupled this with bacterial culturing. Bacterial isolates were mono-associated with axenic B. dorsalis embryos. The shortest embryonic development period was recorded in flies with an intact gut microbiome while the longest period was recorded in axenic fly lines. Similarly, larval development was shortest in flies with an intact gut microbiome, in addition to flies inoculated with Providencia alcalifaciens. Adult B. dorsalis flies emerging from embryos that had been mono-associated with a strain of Lactococcus lactis had decreased survival when challenged with a standard dosage of M. anisopliae ICIPE69 conidia. However, there were no differences in survival between the germ-free lines and flies with an intact microbiome. CONCLUSIONS: These findings will contribute to the selection of probiotics used in artificial diets for B. dorsalis rearing and the development of improved integrated pest management strategies based on entomopathogenic fungi.

Isopentyl Butanoate: Aggregation Pheromone of the Brown Spiny Bug, Clavigralla tomentosicollis (Hemiptera: Coreidae), and Kairomone for the Egg Parasitoid Gryon sp. (Hymenoptera: Scelionidae).

The brown spiny bug, Clavigralla tomentosicollis Stål (Hemiptera: Coreidae) is a key pest of leguminous crops in many countries in Africa, causing significant yield losses especially in cowpea, pigeon pea and common beans. Although C. tomentosicollis uses olfaction to aggregate, little is known about the identity of the aggregation pheromone. This study aimed to identify the aggregation pheromone of C. tomentosicollis and to test its potential role in the behavior of its egg parasitoid, Gryon sp. In Y-tube olfactometer bioassays, only male volatiles strongly attracted both sexes of C. tomentosicollis. Coupled gas chromatography/electroantennographic detection (GC/EAD) and GC/mass spectrometry were used to identify antennally-active compounds from male volatiles. Antennae of both sexes detected identical components including a male-specific component, identified as isopentyl butanoate, which was also detected by antenna of the egg parasitoid. In olfactometer bioassays, both sexes of C. tomentosicollis and the egg parasitoid responded to isopentyl butanoate. These results suggest that isopentyl butanoate serves as an aggregation pheromone for both sexes of C. tomentosicollis and a useful kairomone to attract the parasitoid in the management of C. tomentosicollis.

Molasses Grass Induces Direct and Indirect Defense Responses in Neighbouring Maize Plants.

Plants have evolved intricate defence strategies against herbivore attack which can include activation of defence in response to stress-related volatile organic compounds (VOCs) emitted by neighbouring plants. VOCs released by intact molasses grass (Melinis minutiflora), have been shown to repel stemborer, Chilo partellus (Swinhoe), from maize and enhance parasitism by Cotesia sesamiae (Cameron). In this study, we tested whether the molasses grass VOCs have a role in plant-plant communication by exposing different maize cultivars to molasses grass for a 3-week induction period and then observing insect responses to the exposed plants. In bioassays, C. partellus preferred non-exposed maize landrace plants for egg deposition to those exposed to molasses grass. Conversely, C. sesamiae parasitoid wasps preferred volatiles from molasses grass exposed maize landraces compared to volatiles from unexposed control plants. Interestingly, the molasses grass induced defence responses were not observed on hybrid maize varieties tested, suggesting that the effect was not simply due to absorption and re-emission of VOCs. Chemical and electrophysiological analyses revealed strong induction of bioactive compounds such as (R)-linalool, (E)-4,8-dimethyl-1,3,7-nonatriene and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene from maize landraces exposed to molasses grass volatiles. Our results suggest that constitutively emitted molasses grass VOCs can induce direct and indirect defence responses in neighbouring maize landraces. Plants activating defences by VOC exposure alone could realize enhanced levels of resistance and fitness compared to those that launch defence responses upon herbivore attack. Opportunities for exploiting plant-plant signalling to develop ecologically sustainable crop protection strategies against devastating insect pests such as stemborer C. partellus are discussed.

Agro-ecological options for fall armyworm (Spodoptera frugiperda JE Smith) management: Providing low-cost, smallholder friendly solutions to an invasive pest.

Fall armyworm (FAW), a voracious agricultural pest native to North and South America, was first detected on the African continent in 2016 and has subsequently spread throughout the continent and across Asia. It has been predicted that FAW could cause up to $US13 billion per annum in crop losses throughout sub-Saharan Africa, thereby threatening the livelihoods of millions of poor farmers. In their haste to respond to FAW governments may promote indiscriminate use of chemical pesticides which, aside from human health and environmental risks, could undermine smallholder pest management strategies that depend to a large degree on natural enemies. Agro-ecological approaches offer culturally appropriate low-cost pest control strategies that can be readily integrated into existing efforts to improve smallholder incomes and resilience through sustainable intensification. Such approaches should therefore be promoted as a core component of integrated pest management (IPM) programmes for FAW in combination with crop breeding for pest resistance, classical biological control and selective use of safe pesticides. Nonetheless, the suitability of agro-ecological measures for reducing FAW densities and impact need to be carefully assessed across varied environmental and socio-economic conditions before they can be proposed for wide-scale implementation. To support this process, we review evidence for the efficacy of potential agro-ecological measures for controlling FAW and other pests, consider the associated risks, and draw attention to critical knowledge gaps. The evidence indicates that several measures can be adopted immediately. These include (i) sustainable soil fertility management, especially measures that maintain or restore soil organic carbon; (ii) intercropping with appropriately selected companion plants; and (iii) diversifying the farm environment through management of (semi)natural habitats at multiple spatial scales. Nevertheless, we recommend embedding trials into upscaling programmes so that the costs and benefits of these interventions may be determined across the diverse biophysical and socio-economic contexts that are found in the invaded range.

Detection, Identification, and Significance of Phytoplasmas in Wild Grasses in East Africa.

Plant-pathogenic phytoplasmas found in wild grasses in East Africa could pose a serious threat to the cultivation of Napier grass, Pennisetum purpureum, the most important livestock fodder in the region. To asses this threat, leaves from plants of 33 grass species were sampled from Mbita, Bungoma, and Busia districts in western Kenya; Tarime district in northern Tanzania; and Busia and Bugiri districts in the eastern Uganda to determine which species host phytoplasmas, the identity of the phytoplasmas, and their relationship with disease symptoms. Phytoplasmas were detected using universal primers based on conserved phytoplasma-specific 16S rDNA sequences from 11 grass species collected. Sequence and phylogenetic analysis revealed the presence of Napier grass stunt-related phytoplasmas in 11 grass species, 'Candidatus Phytoplasma cynodontis' in three, and goosegrass white leaf phytoplasma in 2 wild grass species. This study showed that the geographical distribution, diversity of phytoplasmas, and their grass host species in East Africa is greater than antecedently thought and that typical disease symptoms, including white leaf or stunting alone, are not reliable indicators of the presence of phytoplasma. It also shows the need to identify insect vectors responsible for phytoplasma transmission from native grasses to Napier grass or other cereals present in the region.

Gut microbiota of Busseola fusca (Lepidoptera: Noctuidae).

Busseola fusca (Fuller) (Lepidoptera: Noctuidae) is a stemborer pest that attacks maize (Zea mays) throughout sub-Saharan Africa. Genetically modified maize has been shown to be effective against B. fusca. However, resistance of B. fusca against Bt-maize has developed and spread throughout South Africa. Previous studies suggested that gut microbiota contribute to mortality across a range of Lepidoptera. To fully assess the role of microbiota within the gut, it is essential to understand the microbiota harboured by natural B. fusca populations. This study aimed to identify the gut-associated bacteria by 16S rRNA gene sequencing. A total of 78 bacterial strains were characterised from the midgut of B. fusca larvae that were collected from 30 sites across the maize producing region of South Africa. Molecular phylogenetic analyses revealed bacteria affiliated to Proteobacteria, Actinobacteria, and Firmicutes. Taxonomic distribution placed these isolates into 15 different genera representing 20 species. The majority of bacteria identified belong to the genera Bacillus, Enterococcus, and Klebsiella. The B. fusca gut represents an intriguing and unexplored niche for analysing microbial ecology. The study could provide opportunities for developing new targets for pest management and contribute to understanding the phenomenon of resistance evolution of this species.

Responses of parasitoids to volatiles induced by Chilo partellus oviposition on teosinte, a wild ancestor of maize.

Maize, a genetically diverse crop, is the domesticated descendent of its wild ancestor, teosinte. Recently, we have shown that certain maize landraces possess a valuable indirect defense trait not present in commercial hybrids. Plants of these landraces release herbivore-induced plant volatiles (HIPVs) that attract both egg [Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae)] and larval [Cotesia sesamiae Cameron (Hymenoptera: Braconidae)] parasitoids in response to stemborer egg deposition. In this study, we tested whether this trait also exists in the germplasm of wild Zea species. Headspace samples were collected from plants exposed to egg deposition by Chilo partellus Swinhoe (Lepidoptera: Crambidae) moths and unexposed control plants. Four-arm olfactometer bioassays with parasitic wasps, T. bournieri and C. sesamiae, indicated that both egg and larval parasitoids preferred HIPVs from plants with eggs in four of the five teosinte species sampled. Headspace samples from oviposited plants released higher amounts of EAG-active compounds such as (E)-4,8-dimethyl-1,3,7-nonatriene. In oviposition choice bioassays, plants without eggs were significantly preferred for subsequent oviposition by moths compared to plants with prior oviposition. These results suggest that this induced indirect defence trait is not limited to landraces but occurs in wild Zea species and appears to be an ancestral trait. Hence, these species possess a valuable trait that could be introgressed into domesticated maize lines to provide indirect defense mechanisms against stemborers.

A new distribution and host record for the rare moth, Callioratis millari (Lepidoptera: Geometridae), and some ecological observations.

Callioratis millari Hampson (Lepidoptera: Geometridae) is a Critically Endangered moth endemic to South Africa. Despite extensive searches, it was previously known only from the Entumeni Nature Reserve in KwaZulu-Natal, where its larvae exclusively feed on the cycad Stangeria eriopus (Kunze) Baill (Cycadales: Stangeriaceae). In July 2022, a new population of C. millari was discovered in the Kabouga section of Addo Elephant National Park in the Eastern Cape. Larvae of C. millari were feeding on the cycad Encephalartos caffer (Thunb.) Lehm (Cycadales: Zamiaceae), which also constitutes a new host record. In June 2023, we determined larval incidence and herbivory at this new locality, offering insights into the ecological requirements of C. millari. Known C. millari localities, although ecologically different, share low altitudes (700-950 m a.s.l.), moderate to high rainfall, and grassy habitats with sparse woody cover. A total of 59 larvae were counted in Kabouga, mostly in the fifth and sixth (final) instars. Herbivory incidence was lower on smaller plants and those covered by other vegetation. The flight period of adult C. millari likely occurs between mid-March and April in Kabouga, but further investigation is needed to clarify this. The peak period of larval occurrence in Kabouga occurs during the driest and coldest months of the year (May-July). Considering limited habitat availability, host plant poaching, and the risk of untimely fires, the species should be considered highly threatened. This study adds to our understanding of the biology of C. millari and provides information on its ecological requirements and may contribute to making informed management decisions.

The Effect of Wood Ash and Soil Applications on the Behavior and Survival of Spodoptera frugiperda (Lepidoptera: Noctuidae) Larvae on Maize.

Cryptic feeding inside maize whorls makes it difficult to control fall armyworm (FAW). Smallholder farmers use alternative methods of control, of which the efficacy is uncertain. We determined the efficacy of wood ash and soil for the control of FAW and recorded its effect on larval preference and ballooning. Maize plants were artificially infested with larvae of different instars and treatments were either soil, wet ash, or dry ash, applied as single preventative or curative applications. Larvae exhibited non-preference for treated leaves in choice tests. The efficacy of treatments varied largely between experiments. Under laboratory conditions, ash treatments resulted in significant mortality of 1st and 5th instars. Dry and wet ash as curative applications for 1st instars resulted in 67 and 66% mortality, respectively, compared to mortality recorded in the control (22%). Under field conditions, survival of 3rd instars on treated plants was low (21-34%), compared to 70% on untreated plants. Due to the high variability in efficacy, the use of these alternative methods does not guarantee effective control. They do, however, have a place in IPM systems if applied as soon as infestations are observed and when larvae as still small. Recommendations on the use of ash and soil as spot treatments against FAW are provided.

Documenting Mantodea species in South African museum collections and an updated species list.

Background: The previous species list of South African Mantodea, published in 1998, was largely compiled from the literature and did not incorporate data from the many insect museum collections available in the country. It is estimated that approximately 120 species of Mantodea occur in South Africa; however, since no historical museum records were previously incorporated, the current information is considered to be outdated and not a true reflection of the Mantodea fauna within this region. A checklist of species is an important benchmark for any insect group, especially in light of the worldwide declines of insect diversity reported over the last decade. Checklists that provide accurate information on insect diversity, especially for groups, such as the Mantodea which could be under threat and thus could provide important information that can be used in determining the threat status of species, as well as to aid in their conservation in general. New information: This paper provides an updated checklist of the praying mantids (Insecta, Mantodea) species of South Africa. While 120 species were previously reported to occur in South Africa, this paper reports 157 species in 64 genera that represent eight different superfamilies, 14 families and 22 subfamilies. Additionally, five species are reported for the first time to occur in South Africa. This species list was generated from the approximately 4000 specimen records of which 3558 records reside within South Africa. The remaining 732 records represent 14 other African countries. Occurrence records from two citizen-science platforms (iNaturalist and Gbif.org), were also incorporated in this study, adding 1880 species records in South Africa. The low number of specimens in the national collections indicate that this group of insects is poorly collected and highlights the lack of knowledge about South Africa's mantid fauna, as well as a lack of taxonomic expertise as 1532 museum specimens remain unidentified to species level.

Residual activity of spinosad applied as a soil drench to tomato seedlings for control of Tuta absoluta.

BACKGROUND: Tuta absoluta (Lepidoptera: Gelechiidae) is difficult to control by means of foliar insecticides, partly because of the endophytic feeding behavior of its larvae. The biopesticide spinosad is applied as a foliar spray for control of T. absoluta and has systemic properties when applied as a soil drench to the growing medium of tomato plants. The aims of this study were to determine the: (i) instar-dependent tolerance of larvae to spinosad; (ii) efficacy of spinosad drench application for the control of larvae; (iii) residual period of systemic activity of spinosad in leaves and fruit after drenching; and (iv) effect of spinosad drenching on tomato plant growth parameters. RESULTS: The estimated LC50 value (Lethal Concentration at which 50% of the larvae died) differed between instars. The LC50 for second-instar larvae (0.41 ppm) to spinosad was significantly lower than that for third- (0.64 ppm) and fourth-instar (0.63 ppm) larvae. The LC80 value (Concentration at which 80% of the larvae died) for fourth-instar larvae (2.48 ppm) was 2.6- and 1.7-fold higher than that for the second- and third-instar larvae, respectively. The spinosad concentration recorded in leaves at 25 days after treatment (DAT; 0.26 µg g-1 ) was significantly lower than that in leaves sampled at 3, 10 and 15 DAT. High larval mortalities were, however, recorded for the duration of the experiment, which lasted 25 days (equivalent to one T. absoluta generation). CONCLUSION: Systemic spinosad effectively controlled T. absoluta larvae over a prolonged period. However, drenching this insecticide violates the recommendation of the Insecticide Resistance Action Committee to avoid treating consecutive insect generations with the same mode of action and can therefore result in the evolution of insecticide resistance. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effect of herbivore stress on transgene behaviour in maize crosses with different genetic backgrounds: cry1Ab transgene transcription, insecticidal protein expression and bioactivity against insect pests.

Background: Decades after their first commercial release, many theoretical assumptions are still taken for granted in the deployment of genetically modified (GM) crops. Theoretically, in the case of maize, active transcription of the cry1Ab transgene would result in dose-dependent production of the insecticidal Cry1Ab protein, which would in turn induce dose-dependent mortality on lepidopteran pests. We produced data to realistically approach this question by using a model that includes two genetic background contexts from two geographical provenances in Brazil and South Africa, and two lepidopteran pests (Helicoverpa armigera and Spodoptera littoralis). However, in this study, the effect of insect herbivory was superimposed to investigate possible stress-induced effects in transgene expression at three levels: mRNA, protein and bioactivity. Results: Overall, we found that herbivore damage by H. armigera was reflected only at the translational level, with a higher level of Cry1Ab protein measured in the Brazilian crosses under herbivore stress. On the other hand, compared to non-stress growing conditions, the herbivore damage by S. littoralis was not directly reflected in mRNA, protein or bioactivity in the South African crosses. Conclusions: The differences between South African and Brazilian genetic backgrounds, and between the stressor effect of the two herbivores used, highlight the complexity of transgene expression at the agroecological level. Supplementary Information: The online version contains supplementary material available at 10.1186/s12302-023-00815-3.

Effects of Cry1Ab transgenic maize on lifecycle and biomarker responses of the earthworm, Eisenia andrei.

A 28-day study was conducted to determine the effects of the Bacillus thuringiensis Cry1Ab toxin on the earthworm Eisenia andrei. Previously, investigations have been limited to life-cycle level effects of this protein on earthworms, and mostly on E. fetida. In this study several endpoints were compared which included biomass changes, cocoon production, hatching success, a cellular metal-stress biomarker (Neutral Red Retention Time; NRRT) and potential genotoxic effects in terms of Randomly Amplified Polymorphic DNA sequences (RAPDs). NRRT results indicated no differences between treatments (p > 0.36), and NRRT remained the same for both treatments at different times during the experiment (p = 0.18). Likewise, no significant differences were found for cocoon production (p = 0.32) or hatching success (p = 0.29). Conversely, biomass data indicated a significant difference between the control treatment and the Bt treatment from the second week onwards (p < 0.001), with the Bt treatment losing significantly more weight than the isoline treatment. Possible confounding factors were identified that might have affected the differences in weight loss between groups. From the RAPD profiles no conclusive data were obtained that could link observed genetic variation to exposure of E. andrei to Cry1Ab proteins produced by Bt maize.

Modeling the Influence of Abiotic and Biotic Factors on Spatial and Temporal Fluctuations of Prostephanus truncatus (Coleoptera: Bostrichidae) Populations in Mozambique.

The larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), is a serious pest of stored maize in Mozambique and in other African countries. This study investigated the influence of abiotic and biotic factors on populations of P. truncatus at four sites over a two-year period (2013-2014) in Mozambique. Fourteen 250 × 250 m quadrants were selected at each site. Plant species diversity, temperature, precipitation, and relative humidity data were recorded. Pheromone-baited Uni-traps were used to monitor P. truncatus inside each quadrant. In addition, plant species were identified using visual observation and measurement of morphological features of leaves and fruits, and quantified, after which the percentage of host plant species of P. truncatus was determined out of all species in each quadrant. Multiple regression analysis and generalized linear models showed that host plant species dominance, maximum and minimum temperature, relative humidity, and rainfall influenced the variations in P. truncatus abundance. The development of these models of P. truncatus flight activity provides a baseline for further studies predicting dispersal and potential areas of invasion by this pest.

Chemical Control and Insecticide Resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae).

Insecticides and genetically modified Bt crops are the main tools for control of the fall armyworm, Spodoptera frugiperda (J.E. Smith). Since its invasion of Africa, the Far East, and Australia where Bt crops are largely absent, insecticide use has increased and reduced susceptibility to several insecticides used for decades in its native distribution area have been reported. Poor efficacy at field-level is sometimes incorrectly ascribed to pest resistance, while numerous other factors influence efficacy at field-level. In this paper, we review the history of insecticide resistance in S. frugiperda and discuss the influence that life history traits, migration ecology, and chemical control practices may have on control efficacy and resistance evolution. The indirect role that poor national policies have on pesticide use practices, and indirectly on control efficacy and selection pressure is discussed. Evidence shows that local selection for resistance drives resistance evolution. Integrated pest management, rather than reliance on a single tactic, is the best way to suppress S. frugiperda numbers and the over-use of insecticides which selects for resistance.

Insect resistance management facing African smallholder farmers under climate change.

Changes in climatic conditions affect pest populations and ultimately result in increased pest status and yield losses. While pesticide application is usually the first defensive tool used to control pest species that threaten crop production, genetically modified (GM) crops with insecticidal traits (Bt crops) are becoming more common. The indiscriminate and over use of insecticides, and absence of insect resistance management (IRM) strategies ultimately lead to evolution of resistance against these technologies. IRM faces significant challenges in the African context. In this paper we use examples of cotton, maize, cowpea and tomato pests to illustrate their potential to evolve resistance to insecticides and also highlight the importance of IRM strategies, both with regard to the use of pesticides and the cultivation of Bt cotton, Bt maize and Bt cowpea.

A Special Collection: Spodoptera frugiperda (Fall Armyworm): Ecology and Management of its World-Scale Invasion Outside of the Americas.

The Special Collection 'Spodoptera frugiperda (fall armyworm): Ecology and Management of its World-scale Invasion Outside of the Americas' presents reviews and research that address topics of overarching interest and contributes to a better understanding of this pest and its management, now that it has spread outside the Americas. The collection is a combination of invited articles presenting new information published for the first time, invited review papers, and a selection of relevant high-quality articles previously published in Journal of Economic Entomology (JEE). Articles in the Collection, as well as selected citations of articles in other publications, reflect the increase in research on S. frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), which became the most important pest of maize in the world during recent years. This Special Collection addresses a wide range of topics, including pest behavior, host strains, insecticide and Bt protein resistance, biological control, host plant resistance, and yield loss estimates. Topics are presented in context of research primarily conducted in regions outside of the Americas where S. frugiperda has invaded and disrupted crop production to varying degrees. In recognition of further spread, the threat of a S. frugiperda invasion into Europe and potential management options are also presented.

Genetic studies of fall armyworm indicate a new introduction into Africa and identify limits to its migratory behavior.

The fall armyworm, Spodoptera frugiperda (J.E. Smith) is native to the Americas and a major pest of corn and several other crops of economic importance. The species has characteristics that make it of particular concern as an invasive pest, including broad host range, long-distance migration behavior, and a propensity for field-evolved pesticide resistance. The discovery of fall armyworm in western Africa in 2016 was followed by what was apparently a remarkably rapid spread throughout sub-Saharan Africa by 2018, causing economic damage estimated in the tens of billions USD and threatening the food security of the continent. Understanding the history of the fall armyworm invasion of Africa and the genetic composition of the African populations is critical to assessing the risk posed to different crop types, the development of effective mitigation strategies, and to make Africa less vulnerable to future invasions of migratory moth pests. This paper tested and expanded on previous studies by combining data from 22 sub-Saharan nations during the period from 2016 to 2019. The results support initial descriptions of the fall armyworm invasion, including the near absence of the strain that prefers rice, millet, and pasture grasses, while providing additional evidence that the magnitude and extent of FAW natural migration on the continent is more limited than expected. The results also show that a second entry of fall armyworm likely occurred in western Africa from a source different than that of the original introduction. These findings indicate that western Africa continues to be at high risk of future introductions of FAW, which could complicate mitigation efforts.

Susceptibility of Tuta absoluta (Lepidoptera: Gelechiidae) Pupae to Soil Applied Entomopathogenic Fungal Biopesticides.

Management of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in greenhouses and under open-field tomato cultivation relies on an integrated approach, largely targeting the egg and larval stages of the pest. However, little to no research has been done on the efficacy of EPFs for control of the pupal stage. The aims of this study were to determine the susceptibility of T. absoluta pupae to Beauveria bassiana and Metarhizium anisopliae spores applied as soil drench treatments, and the possible effects of these treatments on fecundity and fertility of moths. The lethal concentrations (LC50 and LC80) of the respective products were estimated in dose-response bioassays by exposing pupae in a soil substrate to different concentrations of EPF products. Emerging moths were paired in different combinations, according to EPF exposure treatments after which fecundity and fertility of females were recorded. Pupae in the soil were effectively controlled by all EPF products in both bioassays as well as in a growth tunnel experiment. The LC50 value of the B. bassiana oil formulation was significantly lower than that of other treatments. The fecundity of females that were subjected to the B. bassiana oil formulation was significantly lower than that of the control treatment. This study showed the potential of soil drench applications of both B. bassiana and M. anisopliae for control of T. absoluta pupae.

Managing Fall Armyworm in Africa: Can Bt Maize Sustainably Improve Control?

The recent invasion of Africa by fall armyworm, Spodoptera frugiperda, a lepidopteran pest of maize and other crops, has heightened concerns about food security for millions of smallholder farmers. Maize genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) is a potentially useful tool for controlling fall armyworm and other lepidopteran pests of maize in Africa. In the Americas, however, fall armyworm rapidly evolved practical resistance to maize producing one Bt toxin (Cry1Ab or Cry1Fa). Also, aside from South Africa, Bt maize has not been approved for cultivation in Africa, where stakeholders in each nation will make decisions about its deployment. In the context of Africa, we address maize production and use; fall armyworm distribution, host range, and impact; fall armyworm control tactics other than Bt maize; and strategies to make Bt maize more sustainable and accessible to smallholders. We recommend mandated refuges of non-Bt maize or other non-Bt host plants of at least 50% of total maize hectares for single-toxin Bt maize and 20% for Bt maize producing two or more distinct toxins that are each highly effective against fall armyworm. The smallholder practices of planting more than one maize cultivar and intercropping maize with other fall armyworm host plants could facilitate compliance. We also propose creating and providing smallholder farmers access to Bt maize that produces four distinct Bt toxins encoded by linked genes in a single transgene cassette. Using this novel Bt maize as one component of integrated pest management could sustainably improve control of lepidopteran pests including fall armyworm.