During its annual general meeting held in Nairobi, Kenya, in November 2017, the icipe Governing Council, will consists of globally reknowned scientists, honoured six outstanding postgraduate scholars, currently undertaking their research at the Centre.

Best published science paper by an icipe scholar

Annette O. Busula (Female, PhD)

icipe supervisor – Dr Daniel Masiga

Paper:  Busula A.O., Bousema T., Mweresa C.K., Masiga D., Logan J.G., Sauerwein R.W., Verhulst  N.O., Takken W. and de Boer J.G. (2017) Gametocytemia and attractiveness of Plasmodium falciparum–infected Kenyan children to Anopheles gambiae mosquitoes. The Journal of Infectious Diseases 0000, 1–5. doi: 10.1093/infdis/jix1214

Contribution to science:  A dual-choice olfactometer experiment using four groups of Kenyan school children, malaria-free, asexual, submicroscopic or microscopic gametocyte carriers aged 5-12 years, versus a standardized human odour was carried out. All children were screened for presence of malaria parasites using microscopy and two molecular techniques, PCR and QT-NASBA, at two time-periods, during infection and after treatment of infected children with artemisinin-lumefantrine. Only the malaria-free children were recruited in the study based on PCR results. Our findings showed that children attracted higher numbers of mosquitoes than the standardized human odour. Additionally, higher attractiveness of malaria-infected persons, (two times more in microscopic gametocyte carriers) is dependent on higher levels of gametocytaemia, compared to children without gametocytes or with low levels of gametocytaemia. Further, not only body odours, but also breath could have contributed to increased attractiveness of microscopic gametocyte carriers before antimalarial treatment. Additional results showed that the attractiveness of the microscopic gametocyte carriers was not influenced by their age and gender, and did not differ significantly with that of the other groups after treatment of infected children with anti-malarials (21 days post-treatment).  The novel results show that high levels of gametocytaemia were associated with high attractiveness of children compared to children without gametocytes or with low levels of gametocytaemia. Additionally, the presence of submicroscopic gametocytes did not contribute significantly to attractiveness. Furthermore, attractiveness of the children to An. gambiae was not influenced by gender or age of children, although Hb significantly affected mosquito attraction, with lower Hb levels associated with higher attraction. The combined findings strongly support the hypothesis that Plasmodium gametocytes, and not asexual stages, mediate the attractiveness of mammalian hosts to mosquitoes and it is dependent on high levels of gametocytaemia. Current epidemiological models do not take into account heterogeneous biting related to gametocyte-mediated attractiveness and disproportionate infection rates resulting from different levels of gametocytaemia. Results from this study will therefore be helpful in mathematical models of malaria transmission.

Funding: This work was supported by the Netherlands Organization for Scientific Research, divisions of Medical Science (TOP Grant 91211038 to W. T.) and Earth and Life Sciences (VIDI Fellowship Grant 016.158.306 to T. B.).  The views expressed herein do not necessarily reflect the official opinion of the donors

University: The scholar was registered at Laboratory of Entomology, Wageningen University, Netherlands.

Ruth Muthoni Kihika – MSc Scholar

icipe Mentors – Dr Baldwyn Torto

Paper:   Kihika R.M., Murungi L.K., Ng’ang’a M.M., Coyne, D.L., Teal, P.E.A., Hassanali A., and Torto B. (2017) Parasitic nematode Meloidogyne incognita interactions with different Capsicum annum cultivars reveal the chemical constituents modulating root herbivory, Nature Scientific Reports 7, 2903, doi: 10.1038/s41598-017-02379-8

Contribution to science:  This paper describes the semiochemical basis of root-knot nematode host seeking behavior. Root-knot nematodes (RKNs), of the genus Meloidogyne, are economically important plant parasitic nematodes that parasitize nearly every species of higher plants including high value vegetable crops such as tomato and pepper and are distributed worldwide. In Africa, crop production losses of up to 100% are encountered especially by small holder farmers. The mitigation measures deployed to control these parasites have had minimal success in addition to the most effective nematicides being discontinued due to their ozone depleting effects. As such, in order to contribute to the development of alternative eco-friendly strategies, the authors investigated the mechanisms of RKN host location. Specifically, the study sought to test the hypothesis that infective second stage juveniles (J2s) of Meloidogyne incognita use volatile chemical signals to locate the roots of the solanaceous plant, Capsicum annum. The host seeking behavior of M. incognita J2s to three cultivars and one accession was evaluated using behavioral assays and chemical analyses. The J2s showed preference for the roots of the three RKN-susceptible cultivars (70-82%) than the accession (47%) over sand controls, suggesting the involvement of chemical cues in host selection and discrimination. Further chemical analysis followed by laboratory behavioral assays showed that a blend of five compounds− methyl salicylate (MeSA), α-pinene, limonene, tridecane, and 2-methoxy- 3-(1-methylpropyl)-pyrazine) common to the four varieties elicited positive behavioral responses. Of the five, MeSA elicited the highest response while the rest of the compounds had intermediate to low effects. On the other hand, thymol present only in the accession induced negative responses. In binary assays, the 5-component blend mixed with thymol versus a control induced avoidance behavior. A similar response was observed when thymol was combined with an attractive plant and tested against a control. These findings clearly demonstrate the role of VOCs in RKN host seeking behavior and the responses induced by thymol allude to its potential as a candidate RKN repellent warranting further investigation in field trials.

The findings contribute to pest management by providing semiochemical-based tools for controlling these economically important RKNs that impact on food security. Importantly, this is a first report of the role and identity of specific plant chemical signals mediating host-RKN interaction. The positive response elicited by MeSA to the J2s, a compound common to the three cultivars and the accession suggests its potential as an attractant which can be exploited in an ‘attract and kill’ strategy to reduce nematode infestation. Furthermore, the reduced nematode responses induced by thymol present only in the accession, highlights its repellent potential in disrupting the chemotactic host finding of the J2s. The outcome of this research can be used to link molecular tools with biochemical processes for the management of RKNs.

Our findings provide new insights for plant breeding whereby specific molecular pathways for suppressing root production of MeSA or incorporating genes responsible for thymol production in the roots of pepper can be explored to protect pepper from this polyphagous pest.

Funding: We gratefully acknowledge the financial support for this research by the following organizations and agencies: United States Department of Agriculture/Agricultural Research Service, Grant No. 58-6615-3-011 F; UK’s Department for International Development (DFID); Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); and the Kenyan Government. We also acknowledge the two anonymous reviewers whose valuable input contributed to improving the manuscript. The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar was registered at Kenyatta University, Kenya.

David K. Mfuti

icipe Mentors – Drs. Subramanian Sevgan / Sunday Ekesi /Saliou Niassy

Paper: Mfuti D.K., Niassy S., Subramanian S., du Plessis H., Ekesi S. and Maniania N.K. (2017) Lure and infect strategy for application of entomopathogenic fungus for the control of bean flower thrips in cowpea. Biological Control 107, 70–76.

Contribution to science:  The use of entomopathogenic fungi (EPF) in horticulture is gaining momentum in Africa and worldwide over the last few years. Biopesticides are generally applied through inundative/cover spray, which requires high amount of inoculum and applied biopesticide has a shorter persistence due to solar radiations. Shorter persistence necessitates repeated applications. High inoculum and repeated applications enhances the cost of biopesticide application significantly, subsequently low uptake. Therefore, there is a need to develop improved application strategy for biopesticides to overcome these limitations and make them affordable for smallholder growers. The use of semiochemicals to lure large number of insects in a trap that can then be inoculated with EPF commonly referred as “autodissemination” has been reported in several cases. This technique is attractive as it has the advantage of higher persistence of biopesticides in comparison to the cover spray application, however the cost of the trapping device could beyond the means of smallholders. However, the integration of pheromones and kairomones in thrips management can offer new perspectives for application of EPF. The kairomone Lurem-TR is attractive of bean flower thrips (BFT) adults and is being used for monitoring thrips populations. We therefore hypothesized that spot-spray application of EPF in combination with thrips attractant could reduce the quantity of inoculum, sustain the efficacy and thereby the cost of EPF use for thrips management especially smallholders. The objective of this study was therefore to evaluate the efficacy and cost benefit analysis of spot-spray in combination with the attractant Lurem-TR and cover spray applications of the entomopathogenic fungus, M. anisopliae for the management of BFT on cowpea crop.  Spot-spray application of biopesticides is an innovative approach that could make EPF application affordable for smallholders for thrips management. This study has demonstrated that spot-spray of EPF in combination with thrips attractant is as effective as cover spray for controlling BFT, while simultaneously being economically viable that gives high rate of return.

Funding: This work was conducted with funding from the German Academic Exchange Service (DAAD) through icipe’s African Regional Postgraduate Programme in Insect Science (ARPPIS), the African Union through the African Union Research Grant Contract no: AURG/108/2012 and the BMZ (The German Federal Ministry for Economic Cooperation and Development) through GIZ (Deutsche Gesellschaft fur Internationale Zusammenarbeit) Project number: 11.7860.7-001.00, Contract number: 81141840.   The views expressed herein do not necessarily reflect the official opinion of the donors.

University: The scholar was registered at North West University, South Africa.

Best poster category

Nancy Karimi Njeru – PhD Scholar

Poster title: Effect of Stemborer Management under Push-Pull Cropping System on Ear Rots of Maize in Western Kenya

Supervisors: Nancy Karimi Njeru*, Prof Zeyaur R Khan, Dr Charles A.O. Midega, Prof. James W. Muthomi* and Dr. Maina J. Wagacha*

International Centre of Insect Physiology and Ecology (icipe), Nairobi, Kenya; and *University of Nairobi, Kenya.

Brief Summary: Aflatoxin and fumonisin are widespread mycotoxins of maize that pose great health risks to consumers of contaminated maize. Different aflatoxin and fumonisin levels in maize from various parts of Kenya have been reported. Since little has been done about their management, especially pre-harvest, the objective of this study was to determine the impact of stem borer management under the push-pull cropping system on maize ear rots, mostly caused by mycotoxin producing fungi. Push-pull cropping system is an integrated technology that controls stemborer and Striga and increases soil fertility, yields and fodder. The study assessed incidence of stem borer infestation at milk growth stage of maize as number of damaged plants out of 100 selected plants in each plot, a push-pull or maize sole crop and severity on a scale of 0-4, (0=no visible damage, 1=slight damage, 2=moderate damage, 3=serious damage, 4=dead heart). At harvest, we determined incidence of ear rots as the number of infected ears out of 100 randomly selected cobs per plot while severity was determined on a scale of 0 – 5 (0 = 0% infection; 1 = 1-10%; 2 = 11–25%; 3 = 26–50%; 4 = 51–75%; 5 = 76–100%). The data obtained indicated significant reduction in stemborer infestation under push-pull which corresponded with a significant reduction in ear rots of maize, especially of Fusarium ear rot, caused by Fusarium spp., producer of fumonisin. The reduced occurrence of maize stem borer infestation and subsequent reduction of maize ear rots could subsequently result in reduction in contamination of the maize with associated mycotoxins. Maize samples from the two systems should be analyzed for major mycotoxins, especially aflatoxin and fumonisin.

Funding: This work was conducted with funding from the German Academic Exchange Service (DAAD) through icipe’s African Regional Postgraduate Programme in Insect Science (ARPPIS), and icipe core funding provided by UK Aid from the UK Government, Swedish International Development Cooperation Agency (Sida), the Swiss Agency for Development and Cooperation (SDC), and the Kenyan Government. The views expressed herein do not necessarily reflect the official opinion of the donors.

Faith Akinyi Obange – MSc Scholar

Poster title:     On the Trail of a Killer: A Multi Locus Sequence Typing Approach to Characterizing Deformed Wing Virus Strains”

Supervisors:   Faith Akinyi Obange*, Dr. J. Villinger, Dr. M. Lattorff and Dr C. Adhiambo

International Centre of Insect Physiology and Ecology (icipe), Nairobi, Kenya; and

*University of Nairobi, Kenya

Brief Summary:  Deformed Wing Virus (DWV) is the deadliest and most widespread of honeybee viruses. With a mortality rate of up to 100%, the lethal strain of DWV threatens global honeybee populations with consequent negative effects on crop pollination, global food security, ecological biodiversity and the apiculture industry. The accurate identification of lethal DWV strains is complicated by a wide diversity of commonly occurring non-lethal DWV strains. Since DWV strains undergo frequent recombination, conventional detection based on amplification of a single genomic locus via qPCR is inadequate for differentiating strains. This necessitates development of multi-locus sequence typing (MLST) approaches for detection and identification of potentially lethal DWV strains. In this project, we developed a high-resolution melting (HRM)-based MLST approach for identifying and characterizing different DWV strains and their recombinants within honeybee populations in Karura Forest, Kenya. We sampled five honeybees each from ten hives in each of two apiaries, extracted viral RNA; reverse transcribed it to cDNA and then amplified it by real-time PCR. We performed HRM analysis by melting the amplicons to generate viral sequence-specific HRM profiles. We cleaned up the PCR products, sequenced them and then performed multi locus sequence typing comparisons. Results indicated the presence of both, lethal and non-lethal DWV strains with marked levels of sequence diversity. Therefore, this method increases the detection accuracy of DWV strains and can detect bottlenecks in DWV viral diversity; a phenomenon found to result in emergence of a dominant DWV strain, which has been associated with colony collapse. This methodology could serve as an early warning tool to predict colonies at risk of collapse and give beekeepers the opportunity to put in place appropriate preventative measures to protect their honeybees.

Funding: This work was conducted with funding from the German Academic Exchange Service (DAAD) through icipe’s African Regional Postgraduate Programme in Insect Science (ARPPIS), and icipe core funding provided by UK Aid from the UK Government, Swedish International Development Cooperation Agency (Sida), the Swiss Agency for Development and Cooperation (SDC), and the Kenyan Government. The views expressed herein do not necessarily reflect the official opinion of the donors.

Seydou Diabaté – PhD Scholar

Poster Title:    Effect of host and non-host volatiles on the behaviour of Megalurothrips sjostedti

Supervisors: Seydou Diabaté*, Dr Thibaud Martin** and Dr Emilie Delétré**, Dr. Sunday Ekesi; Dr. Komi Fiaboe, *Dr. Lucy K. Murungi and *Prof. J. Wesonga.

International Centre of Insect Physiology and Ecology (icipe), Nairobi, Kenya; **The French Agricultural Research Centre for International Development (CIRAD) and *Jomo Kenyatta University of Agriculture and Technology, Juja, Kenya.

Brief summary:  In sub-Saharan Africa, feeding by bean flower thrips (BFT) (Megalurothrips sjostedti) (Thysanoptera: Thripidae) causes shedding of cowpea (Vigna unguiculata) flower buds and flowers. The chemical sprays that farmers use to control thrips have a negative impact on human health and the environment. Use of host and non-host volatiles is an alternative to reducing chemical pesticide application in an integrated pest management (IPM) strategy. We hypothesized that cowpea emits defense/repellent plant volatiles and that herbal plant volatiles could decrease the attractiveness of its host odour. We evaluated the attractiveness of vegetative and flowers parts of four cowpea varieties (KK1, K80, M66 and eL) and two herbal plants, Cymbopogon citratus and Tagetes minuta to male and female M. sjostedti using Y-tube olfactometer. With the exception of the flowers of cowpea variety KK1 which were attractive to female M. sjostedti, all the varieties induced repellence or neutral responses to both sexes of the pest. Combination of KK1 flower with either C. citrates cut leaves or T. minuta plant were less attractive than cowpea flower alone (KK1) for females. However, the inhibitory effect of C. citratus cut leaves disappeared after 24 hours. Overall, these results highlight the potential of exploiting volatiles from repellent plants to reduce M. sjostedti infestation in cowpea cropping systems.

Funding: This work was conducted with funding from The Federal Ministry for Economic Cooperation and Development (BMZ) and Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, Project Number: 13.1432.7-001.00 & Grant No. 81170265, and icipe core funding provided by UK Aid from the UK Government, Swedish International Development Cooperation Agency (Sida), the Swiss Agency for Development and Cooperation (SDC), and the Kenyan Government. The views expressed herein do not necessarily reflect the official opinion of the donors.