During its Annual General Meeting held on 18 November 2022, the icipe Governing Council, which consists of globally renowned scientists, honoured seven outstanding postgraduate scholars, currently undertaking their research at the Centre.

Best published science paper by an icipe scholar

Rehemah Gwokyalya (PhD, Uganda)

icipe mentors: Dr Samira A. Mohamed, Jeremy K. Herren, Shepard Ndlela and Fathiya Khamis

Paper: Gwokyalya R, Herren JK, Weldon CW, Khamis FM, Ndlela S and Mohamed SA (2022) Differential immune responses in new and old fruit fly-parasitoid associations: Implications for their management. Front. Physiol. 13:945370. https://doi.org/10.3389/fphys.2022.945370 IF 4.755

Contribution to science: Fruit fly pests represent a major impediment to horticultural production across Africa. For example, following the invasion of Bactocera dorsalis, an estimated loss of horticultural produce equating to USD 2 billion annually, was reported for sub-Saharan Africa. The management of tephritid fruit flies heavily relies on the use of insecticides, many of which are not eco-friendly. This prompted the search for alternative eco-friendly management strategies like the use of parasitoids. However, the success of parasitoids in the suppression of these pests is highly variable, hence affecting the outcome of parasitoid-oriented biological control programs. In this study, we demonstrated that cellular immune responses of the fruit fly pests, B. dorsalis and Ceratitis cosyra are central to the successful development and emergence the parasitoids, Diachasmimorpha longicaudata and Pystallia cosyrae.

We showed that resistance to parasitoids is related to the number of circulating hemocytes in the host fruit fly. The higher hemocyte counts in B. dorsalis compared to C. cosyra increased the likelihood that, upon parasitoid invasion, more B. dorsalis cells will be activated and attached to the parasitoid egg culminating into encapsulation and eventual melanisation of the parasitoid egg/larva. Successful encapsulation and melanisation led to asphyxiation of the parasitoid egg/larva resulting in the death of the immature parasitoid.

We further illustrated that the alien parasitoid species, D. longicaudata was able to suppress the immune responses of both fruit fly species suggesting that this parasitoid is a stronger natural enemy than P. cosyrae and represents a formidable agent for use in biological control of both B. dorsalis and C. cosyra. These findings elucidate the importance of cellular immunity in host defence against natural enemies and shed light of the possible mechanisms employed by parasitoids to overcome these host-mediated cellular defences. These results further provide information on the most effective parasitoid species for use in biocontrol of tephritid fruit flies, and possible ways through which parasitoid performance can be improved for more efficient and sustainable integrated management of fruit fly pests. This will reduce over reliance on chemical pesticides and improve the quality and quantity of horticultural produce. This will translate into enhanced income of fruit and vegetable farmers across sub-Saharan Africa and beyond.

Funding: This work received financial support from International Development Research Centre (IDRC) and the Australian Centre for International Agricultural Research (ACIAR) for the project “Alien invasive fruit flies in Southern Africa: Implementation of a sustainable IPM programme to combat their menaces (grant number 109040)”. Also, the authors gratefully acknowledge the financial support for this research by the following organizations and agencies: the Norwegian Agency for Development Cooperation (NORAD), the Section for research, innovation, and higher education for the project “Combatting Arthropod Pests for better Health, Food and Climate Resilience (grant number RAF-3058 KEN-18/0005)”; the Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Australian Centre for International Agricultural Research (ACIAR); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya. The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar is registered at the University of Pretoria, South Africa.

Miano Raphael Njurai (PhD, Kenya)

icipe mentor: Dr Samira A. Mohamed

Paper: Miano, R. N., Ayelo, P. M., Musau, R., Hassanali, A., & Mohamed, S. A. (2022). Electroantennogram and machine learning reveal a volatile blend mediating avoidance behavior by Tuta absoluta females to a wild tomato plant. Scientific Reports, 12(1), 1–16. https://doi.org/10.1038/s41598-022-13125-0

Contribution to Science: Tomato cultivation is threatened by infestations of the nocturnal invasive tomato pinworm, Tuta absoluta. This study was based on field observations that a wild tomato, Solanum lycopersicum var. cerasiforme, growing in Mount Kenya region, Kenya, is less attacked by T. absoluta, unlike the cultivated tomatoes like S. lycopersicum (var. Rambo F1). We hypothesized that the wild tomato may be actively avoided by gravid T. absoluta females because of the presence of oviposition-deterrent allelochemical constituents. We compared the infestation levels of Tuta absoluta in the field monocrops and intercrops of the wild tomato and cultivated commercial tomato and found significant reductions in infestation levels in the monocrop of the wild tomato, and intercrops of wild and cultivated tomato plants compared to the monocrop of the cultivated tomato. We further characterized the headspaces using gas chromatography-linked mass spectrometry (GC-MS) of the two genotypes released during the day and at night where both quantitative and qualitative differences were noted. The headspaces were also analyzed using gas chromatography-linked electroantennography (GC-EAD). A total of 16 compounds namely hexanal, (Z)-3-hexenol, α-pinene, β-myrcene, α-phellandrene, β-phellandrene, (E)-β-ocimene, terpinolene, limonene oxide, camphor, citronellal, methyl salicylate, (E)-β-caryophyllene, 3,7,7-trimethyl-1,3,5-cycloheptatriene, germacrene D and cis-carvenone oxide were detected by antennae of female T. absoluta. Among these EAG-active volatiles, a blend of hexanal, (Z)-3-hexenol, limonene oxide and camphor which were only found in headspaces of the wild tomato showed dose-dependent repellence to the females in wind tunnel experiments. These results show that the wild tomato produces a volatile blend that is not attractive to Tuta absoluta and hence provides some groundwork for the exploitation of the allelochemicals of the wild tomato in the development of novel integrated pest management of T. absoluta.

Funding: (i)The German Federal Ministry for Economic Cooperation and Development (BMZ) commissioned and administered through the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) Fund for International Agricultural Research (FIA) (grant number:  81157481).  (ii) The Biovision Foundation Tuta IPM project (project ID: BV DPP-012/2019-2021); the Norwegian Agency for Development Cooperation, the section for research, innovation and higher education (grant number: RAF-3058 KEN-18/0005); the Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Australian Centre for International Agricultural Research (ACIAR); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya. The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar is registered at Kenyatta University, Nairobi, Kenya

Nelly Chepkosgei Maiyo (MSc, Kenya)

icipe mentors: Dr. Chrysantus M. Tanga, Dr. Fathiya M. Khamis

Paper: Maiyo, N.C.; Khamis, F.M.; Okoth, M.W.; Abong, G.O.; Subramanian, S.; Egonyu, J.P.; Xavier, C.; Ekesi, S.; Omuse, E.R.; Nakimbugwe, D.; Ssepuuya, G.; Ghemoh, C.J.; and Tanga, C.M. Nutritional Quality of Four Novel Porridge Products Blended with Edible Cricket (Scapsipedus icipe) Meal for Food. Foods 2022, 11, 1047. https:// doi.org/10.3390/foods11071047

Contribution to science: Malnutrition is a serious health concern in sub–Saharan African (SSA) countries. Protein-energy malnutrition (PEM) and deficiencies of important micronutrients including iron, zinc, and vitamin A are the most common forms of malnutrition reported in these countries. Porridge serves as an important complementary food and traditional beverage across the African continent, hence an ideal staple food for biofortification. The traditional porridge is mainly prepared from cereals and tubers which have considerably low essential amino acids and micronutrients necessary for healthy growth. Africa is home to a diverse range of edible insects and current studies have established that these insects are packed with essential nutrients with great potential to substantially reduce malnutrition. However, they remain underutilized in terms of food-to-food biofortification. Therefore, this study demonstrated the importance of integrating cricket into cereal-based porridge, resulting in nutrient-dense porridge products sufficient to meet the RDA of the most vulnerable groups in the population. Fortified porridge products had twice as much protein, three to four times more crude fat and double the amount of zinc and iron when compared to commercially available brands. The use of processing technologies such as germination and fermentation enhanced the bioavailability of most nutrients particularly minerals, vitamins and essential fatty acids including omega-3 fatty acids in all the porridge products formulated. The knowledge and findings of this study can be adapted in low and middle income counties to help alleviate malnutrition among women and children who bear the brunt of the malnutrition burden. The findings can also help assess the feasibility and commercial viability of insect-based food products as well as put focus and attention on underutilized indigenous crops that have great potential to influence food security and promote sustainable rural growth and development.

Funding: BioInnovate Africa Programme (INSBIZ—Contribution ID No. 51050076); the Curt Bergfors Foundation Food Planet Prize Award; Bill & Melinda Gates Foundation (INV032416); Canadian International Development Research Centre (IDRC); the Australian Centre for International Agricultural Research (ACIAR) (INSFEED—Phase 2: Cultivate Grant No: 108866– 001); Norwegian Agency for Development Cooperation, the section for research, innovation, and higher education grant number RAF–3058 KEN–18/0005 (CAP–Africa); the Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Australian Centre for International Agricultural Research (ACIAR); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya. The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar is registered at University of Nairobi, Kenya.

Nelson Litunya Mwando (PhD, Kenya)

icipe mentors: Dr. Shepard Ndlela, Dr. Sevgan Subramanian and Dr. Samira A. Mohamed

Paper: Mwando, N. L., Ndlela, S., Meyhöfer, R., Subramanian, S., & Mohamed, S. A. (2022). Immersion in hot water as a phytosanitary treatment for Thaumatotibia leucotreta (Lepidoptera: Tortricidae) in bell pepper (Capsicum annuum L.). Postharvest Biology and Technology, 192, 112026 https://doi.org/10.1016/j.postharvbio.2022.112026

Contribution to science: Our study explores the use of hot water treatment (HWT) technology in disinfestation of false codling moth (FCM) in bell pepper. Bell pepper is an economically important food and cash crop in sub-Saharan Africa, benefitting millions of growers, the majority being smallholders. In Kenya and Uganda, this crop is of significant socio-economic importance, in horticulture as its cultivation offers employment opportunities for women and youth – who make up over 80% of the agricultural labour force – and provide essential nutrients for the communities. Despite these qualities, production and trade of the bell pepper is constrained by several insect pests, chiefly FCM. Not only does this pest potentially cause yield losses of between 60-90%, it also restricts access to regional and lucrative international export markets for affected capsicum as it is classified as a quarantine pest. This study demystifies the concept of HWT as an option in postharvest disinfestation more so in vegetables, increases awareness of the robustness of this technology and demonstrates that fresh produce subjected to HWT are not compromised in terms of turgidity, colour, nutritional value or even aesthetic appearance and overall quality. When well utilized, HWT can reduce or eliminate emergence of quarantine pests in new regions and therefore can be incorporated to complement the existing preharvest integrated pest management (IPM) control measures for FCM.

Funding: The authors gratefully acknowledge the financial support for this research by the following organizations and agencies: BioInnovate Africa, grant number: BA-C1-2017-06_icipe; and the Norwegian Agency for Development Cooperation, the section for research, innovation and higher education grant number RAF-3058 KEN-18/0005; the Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Australian Centre for International Agricultural Research (ACIAR); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya. The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar is registered at Leibniz University Hannover, Germany.

Best science poster by an icipe scholar

Evalyne Wambui Ndotono (MSc. Kenya)

Poster title: Gut Microbial shift in Broiler and layer Chicken Fed Black Soldier Fly Larvae-Based Meal as a Dietary Protein Source

Supervisors: Dr Fathiya Khamis and Dr Chrysantus Tanga (icipe), Dr Joel Bargul (Jomo Kenyatta University of Agriculture and Technology)

Brief Summary: Insect-based meal as an alternative source of protein in poultry production is gaining a lot of research attention due to the increased global demand for protein for both animals and humans. However, there is limited information demonstrating the implications of these feeds to the poultry value chain and the chicken gut health. This study, therefore, focused on identifying and characterizing the gut microbial communities of broiler and layer chicken fed black soldier fly larval meal and comparing them to those fed conventional fishmeal. Our findings demonstrated that the incorporation of black soldier fly larvae in chicken diets enhanced the gut health of the chicken by increasing the wealth of beneficial bacteria such as Lactobacillus and Enterococcus. These beneficial microbes identified are very vital in poultry health as they are known probiotics that strengthen immunity by forming protective barriers in the lining of the gut preventing the growth of disease-causing agents. In addition, our findings are significant in the ongoing quest in Africa and globally, to re-evaluate the use of antibiotics in poultry farming which are raising global concerns about the risk of transferring drug-resistant bacteria and antibiotic residues to consumers. As per our results, the use of black soldier fly larvae feeds may preempt over-reliance on antibiotics because they enhance the proliferation of probiotic bacteria in the gut of chickens thus improving their overall health. Black soldier fly feeds could therefore be advocated as a promising and safe feed additive that can replace the unsustainable fishmeal.

Funding: This work received financial support from; the Canadian International Development Research Centre (IDRC) and the Australian Centre for International Agricultural Research (ACIAR) (INSFEED-Phase 2: Cultivate Grant No: 108866-001);  Rockefeller Foundation (SiPFeed—Grant No: 2018 FOD 009); the Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Australian Centre for International Agricultural Research (ACIAR); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya. The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar is registered at Jomo Kenyatta University of Agriculture and Technology, Kenya.

Jacqueline Wahura Waweru (PhD, Kenya)

Poster Title: Investigating Symbiont-Based Immunity in Anopheles Mosquitoes against plasmodium falciparum Infection

Supervisors: Drs. Jeremy Herren and Daniel Masiga – International Centre of Insect Physiology and Ecology (icipe)

Brief Summary: The recently discovered Anopheles symbiont, Microsporidia MB, is maternally inherited and has a strong malaria transmission-blocking phenotype in Anopheles arabiensis, the predominant Anopheles gambiae species complex member in many active transmission areas in eastern Africa. Microsporidia MB therefore is an ideal candidate for developing a strategy for transmission-blocking by vector population replacement. The mechanistic basis of Microsporidia MB Plasmodium transmission blocking has not been elucidated. However, preliminary studies suggest that the endosymbiont may activate the host’s immune system. Here, we determined the impact of Microsporidia MB on the host mosquito immune system by assessing the effect of infection on different mosquito tissues including the fat bodies, midguts, and ovaries using transcriptomics. We observed a downregulation of trypsin and carbopeptidases in Microsporidia MB infected mosquitoes as compared to the non-infected mosquitoes. Trypsins are categorized as serine proteases and are linked to several roles in mosquitoes such as digestion, activation of immune responses through the activation of processes such as the melanization cascade and the activation of Plasmodium falciparum prochitinases which allows the parasite to transverse through the periotrophic matrix. Downregulated trypsins could be associated with the enzyme Plasmodium ookinete chitinase not being activated in MB positive guts and thus preventing the parasite from crossing the midgut epithelial wall limiting the development of ookinetes to oocysts. Microsporidia MB infected ovaries on the other hand exhibited a closely similar gene expression profile with that of ovaries from non-infected mosquitoes, with only one uncharacterized gene being upregulated in the MB infected mosquitoes. These results indicate that mosquito infection with MB in the ovaries is highly nascent. Whether this is adaptive, to maximize transmission by minimizing effects on egg production, will require further investigation. In the fat bodies, genes associated with antioxidant activities e.g. glutathione S transferase were upregulated in Microsporidia MB infected mosquitoes as compared to the non-infected. An upregulation of these genes suggests that Microsporidia MB infected fat bodies were under high oxidative stress as compared to the non-infected fat bodies. This oxidative stress would trigger the release of antioxidants to block apoptosis and necrosis. High oxidative stress could damage the Plasmodium parasite by triggering immune recognition and activation through encapsulation and melanization. In summary, these results suggest that Microsporidia MB could be blocking the transmission of Plasmodium by priming the host immune system either at the local or systemic levels.

Funding: This work is supported by the Bill and Melinda Gates Foundation (INV0225840) and Open Philanthropy (SYMBIOVECTOR Track A). We gratefully acknowledge icipe core funding provided by the Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Australian Centre for International Agricultural Research (ACIAR); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya. The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar is registered at University of the Witwatersrand, Johannesburg, South Africa.

Sahadatou Mama Sambo (PhD, Benin)

Poster title: Combating the tomato pest Tuta absoluta using an assembly of native and exotic parasitoids

Supervisors:

icipe primary supervisor: Dr Samira Abuelgasim Mohamed

icipe co-supervisor: Dr Shepard Ndlela

University supervisor: Prof Hannalene du Plessis

Brief Summary: The invasion of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has increased damage on tomato Solanum lycopersicum L. (Solanaceae), with up to 100% losses. Surveys among tomato producers show that this invasion led to an increased use of synthetic chemicals, with food poisoning risks and negative effects on ecosystem services. Implementing ecologically-based pest control practices can reduce environmental contamination, improve biodiversity conservation, contribute to the protection of human health and increase food security. This poster aims to investigate the interaction between the introduced parasitoid, Dolichogenidea gelechiidivoris Marsh (Hymenoptera: Braconidae) with the native parasitoids for a sustainable Integrated Pest Management. Therefore, short term interspecific competition assays between D. gelechiidivoris and Stenomesius sp. near japonicus (Ashmead) (Hymenoptera: Eulophidae) have been conducted. Assays were also performed to investigate long term interaction between D. gelechiidivoris and the indigenous Bracon nigricans Szépligeti (Hymenoptera: Braconidae). Additionally, infested materiel was collected from D. gelechiidivoris Release areas. The short-term interaction between D. gelechiidivoris and S. sp. nr. japonicus showed the exotic parasitoid performing far better than the native species, without any significant effect in terms of physical aggression, oviposition and progeny development. For the long-term interaction between D. gelechiidivoris and B. nigricans, the native parasitoid negatively affected the growth of the population of the exotic species. However, same level of pest control was observed for this combination as well as in the scenario where each species of parasitoid was alone. The study also reported co-occurrence of the three species in open field tomato where D. gelechiidivoris was previously release.

Funding: The authors gratefully acknowledge the financial support for this research by the following organizations and agencies: Biovision Foundation grant number BV DPP-012/2019-2022; Norwegian Agency for Development Cooperation-(NORAD), the section for research, innovation and higher education grant number RAF-3058 KEN-18/0005; Scaling-up Climate-Smart Pest Management Approaches for Enhanced Maize and Tomato Systems Productivity in Eastern Africa (SCLAMP) grant number 81250394; the Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Australian Centre for International Agricultural Research (ACIAR); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya. The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar is registered at North-West University, Potchefstroom, South Africa.