Applying push-pull principles in managing fall armyworm in Africa CHARLES MIDEGA International Centre of Insect Physiology and Ecology, Nairobi, Kenya
Invasion of fall armyworm (FAW) in Africa FAW invaded Africa in 2016, ravaging cereal crops across >40 countries, causing an annual loss of $6.25 b. The pest threatens to put millions of people at the risk of hunger in Africa.
Key constraints prior to FAW invasion Lepidopteran stemborers were the most injurious pests of cereals in SSA; causing up to 80% yield losses to maize, conservatively $1.5 billion loss annually Striga causes up to total yield loss, affecting about 100 million people Effects are aggravated by poor soil fertility and drought
What is Push-Pull System? Attract natural enemies Moths are pushed away Main Crop Trap Crop Attract moths The push-pull system is a novel approach in pest management, developed by understanding the complex mechanisms that govern the ecology of plants and insects, which uses carefullyselected repellent intercrops and attractive trap plants. Insect pests are repelled from the food crop and are attracted to a trap crop. The repellent intercrop also effectively controls parasitic striga weed.
The push-pull technology 1 cereal + 2 perennial companion crops Conventional push-pull encompasses intercropping maize with the legume desmodium and a border row of Napier grass around the plot; both desmodium and Napier grass are perennial fodder plants
Adaptation of push-pull to climate change Push-pull has been adapted to the increasingly dry and hot conditions associated with climate change. Significant increases in maize and sorghum yields across drier agroecologies in eastern Africa Significant improvements in economic gains to the farmers Midega et al. 2015. Field Crops Research 180, 118 125
Climate-smart push-pull
Components delivering pest control 120 * Mean number of C. partellus eggs/plant 1200 800 400 0 800 600 400 200 Ex- Nyanza1 Napier grass variety Maize Inbred A Clone 13 * Bana * * * Ex- Machakos * Ex- Nyanza2 * % Larval survival 100 80 60 40 20 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 Ex-Nyanza-1 Clone 13 Bana Ex-Machakos Ex-Nyanza-2 French Cameroon Gold Coast Mott Pakistan Hybrid Uganda Hairless Maize 0 French Cameroon Gold Coast Mott Pakistan hybrid Uganda Hairless Days after egg hatch The trap plant is preferred to maize by the pests for egg deposition However, the plant isn t suitable for survival and development of the pests larvae, resulting in high mortality While FAW moths oviposit on Brachiaria mulatoii, the larvae do not feed on the plant Khan, Midega et al., 2006. Entomol. Exp. Appl. 119,15-22 Khan, Midega et al., 2007. Entomol. Exp. Appl. 124, 201-211 Midega et al., 2011. Entomol. Exp. Appl. 138, 40-47
Chemistry of stemborer moth attraction Pennisetum purpureum 3 (Z)-3-hexenyl acetate Napier grass emits higher amounts of greenleaf volatiles that attract stemborer moths relative to maize, making it more visible /attractive Hexanal 1 (Z)-3-hexen-1-ol 2 I.S. Zea mays I.S. 10 15 20 25 Retention time 30 Chamberlain et al., 2006. Journal of Chemical Ecology 32:565-577
Chemistry of the intercrop (E)-ocimene (E)-4,8-dimethyl-1,3,7- nonatriene H H -caryophyllene humulene -terpinolene Intercrop emits volatile organic compounds that repel the pests, including FAW, away from the maize These compounds at the same time attract natural enemies of the pests, resulting in higher parasitism rates in the push-pull farms Midega et al., 2009. Crop Prot. 28, 1045 1051 Midega et al., 2014. Agric. Ecosyst. Environ. 188, 289 293 Khan et al., 2000. Pest Manage Sci 56, 957-962
1= (E)-ß-ocimene; 2= α-terpinolene; 3= β-caryophyllene; 4= humulene; 5= (E)-4,8-dimethyl-1,3,7- nonatriene; 6= α-cedrene; 7= hexanal; 8= (E)-2-hexenal; 9= (Z)-3-hexen-1-ol; 10= (Z)-3-hexen-1-yl acetate ; 11= 5,7,2,4 -tetrahydroxy-6-(3- methylbut-2-enyl)isoflavanone (uncinanone A); 12= 4,5 -dihydro-5,2,4 - trihydroxy-5 -isopropenylfurano- (2,3 ;7,6)-isoflavanone (uncinanone B); 13= 4,5 - dihydro-2 - methoxy-5,4 -dihydroxy-5 - isopropenylfurano-(2,3 ;7,6)- isoflavanone (uncinanone C), 14= di-c-glycosylflavone 6-C- α-l-arabinopyranosyl-8-c-β- Dglucopyranosylapigenin Khan et al., 2010, J. Exp Bot 61, 4185 4196 Midega et al., 2015. Ecol Entomol 40(Sup1), 70-81
Push-pull effectively controls FAW
Push-pull effectively controls FAW Midega et al. 2018. Crop Protection 105, 10 15
Farmers perceptions on FAW damage under push-pull and maize monocrop
Ecological integrity and biocontrol Number of total spiders/ plot % predation of eggs Number of lycosid spiders/plot % predation of larvae Midega et al., 2009, Crop Prot. 28,1045 1051 Midega et al., 2008. J. Appl. Entomol. 132, 248-254 Midega et al., 2006. Int. J. Pest Manage. 52, 1-10 Midega and Khan, 2003. Insect Sci. Appl. 23, 301-308 Spiders significantly more abundant under push-pull Higher species diversity- Shannon s diversity index No species dominance- Berger Parker dominance equation Even distribution of species- Shannon s equitability index Higher pest predation rates
Push-pull, plant signaling and FAW control R H S OH R H S O Growing maize next to molasses grass induces a defence response in the maize making it more attractive to parasitic wasps R = H, nerolidol R = H, geranylacetone (E)-4,8-dimethyl-1,3,7-nonatriene Fe III (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene R H S O O (intermediary) OH
Push-pull improves soil health 0.25 80 Total N (g) / 250 g Soil 0.2 0.15 0.1 0.05 0 Maize Monocrop Maize + Desmodium Maize + Soybean Maize + Sunhemp Maize + Cowpea Intercrops Extractable soil P (ppm) 60 40 20 0 Total soil C (%) 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Total soil carbon PP Mono PP-1998 Mono Treatment Push Pull Monoculture 1 2 3 4 5 6 7 8 Field Pair Number Desmodium adds nitrogen to the soil and has a trailing habit, helping conserve soil moisture. It adds to soil organic matter, enhancing the capacity of the soil to sequester carbon. Increases in organic matter prevents leaching of nutrients, improves plant growth, vigour and ability to compensate for leaf damage by pests
A farmer before and after adopting push-pull BEFORE AFTER
Crop-livestock integration through push-pull The companion plants used in push-pull are high value fodder thus allowing integration of crop and livestock production Expands economic streams of the farmers Improves nutrition Enhances youth and women empowerment
Technology dissemination Field days Farmer Teachers Radio Participatory video Farmer Field Schools
Towards developing sustainable control strategies for FAW in Africa and beyond A. Wide-scale dissemination of push-pull technology in Africa and beyond to immediately reduce damage caused by FAW B. Understand science behind the effective control of FAW through the push-pull technology C. Develop a smart push-pull using trap plants which will reduce FAW population 1. Study host range of FAW 2. Investigate role of chemical cues in control of FAW in push-pull 3. Understand plant-plant signaling below and above ground in influencing FAW behavior effects through volatile emission 4. Impact of landscape complexity affecting FAW 5. Companion plants which could enhance biological control through augmentation and conservation of natural enemies
Push-pull, a platform technology 1. Stemborer control 2. Striga control 3. Fodder provision 4. Climate change adaptation/mitigation 5. Fall armyworm control 6. Mycotoxins control 7. Soil health improvement
Acknowledgement Donors directly providing financial support to icipe Netherlands Directorate- General for International Cooperation.
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