Chemical Ecology for Sustainable Sorghum Production in Ethiopia

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This study was presented during the conference “Production and Carbon Dynamics in Sustainable Agricultural and Forest Systems in Africa” held in September, 2010.

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Chemical Ecology for Sustainable Sorghum Production in Ethiopia

  1. 1. Chemical Ecology for Sustainable Production of Sorghum in Ethiopia Ylva Hillbur, Department of Plant Protection Biology, SLU ABSTRACT: The sorghum chafer can cause devastating damage in ripening sorghum. The chafer is a relatively large (2.5 cm) scarab beetle and twenty or more of them can be found on each sorghum head sucking out kernels in the milky stage. In dry-land parts of Ethiopia, where sorghum is an important staple, crop losses of up to 70% due to sorghum chafer attack have been reported. Conventional management methods have proven unsuccessful in controlling the beetle. The famers have instead developed an alternative method using rotting fruit to attract beetles to a point source of insecticide. The method is built on the fact that the beetles, like most insects, use odors to find food. Although the method is promising fruit is scarce in some regions and the odor bait is thus variable. A synthetic, standardized attractant would allow for constant use as well as for monitoring of beetle populations between regions and seasons. In a joint project between SLU and Addis Ababa University we have studied the biology and chemical ecology of the sorghum chafer and identified two highly active odor attractants. One is a host plant component discovered by electrophysiological screening of the antennal response to a wide range of known fruit and flower volatiles. The other is a pheromone component identified from extracts of the sorghum chafer females. Both compounds catch large numbers of sorghum chafers when used as odor baits in traps in the field. DISCUSSION AFTER PRESENTATION: There was a lot of interest in the project and questions concerned how many insect traps a farmer would need in order to catch enough beetle pests to be effective, and what would the cost be. The project is starting to study this element now and next year but the effectiveness depends partly on the life cycle of the pest and the timing of the trapping. It the traps can be produced cheaply enough it is anticipated that it could prove cost-effective.
  2. 2. Chemical ecology for sustainable production of sorghum in Ethiopia Ylva Hillbur, Department of Plant Protection Biology, SLU
  3. 3. 70% crop loss, difficult to control
  4. 4. Sorghum chafer, Pachnoda interrupta
  5. 5. Fruit can be scarce Variable bait quality
  6. 6. Objectives: 1.Standardize the traps with synthetic plant odor lure as bait 2. Increase efficiency by adding pheromones
  7. 7. Different food sources – which odor signals? Sorghum bicolor Abutilon figarianum
  8. 8. Odor collection
  9. 9. Which odor molecules do the samples contain? Gas chromatography (GC)
  10. 10. GC-EAD (GC-coupled Electro Antennographic Detection) Which odor molecules can the insect smell?
  11. 11. GC-EAD using beetle antennae
  12. 12. Antennal response to sorghum odor 1.Tridecane 2.(Z)-3-Hexenol 3.1-Octen-3-ol 4.1-Octanol
  13. 13. Antennal response to abutilon odor 1.(Z)-3-Hexenol 2.Tetradecane 3.Methyl salicylate 4.Methyl anthranilate
  14. 14. Field testing
  15. 15. Rasa Embuay Bad Field Sites
  16. 16. Field trapping
  17. 17. Wire mesh cage with bait placed here Beetles Wire mesh cage Sex pheromone The trap Odor bait
  18. 18. The sorghum blend: as good as its’ best component
  19. 19. The abutilon blend: as good as its’ best component
  20. 20. • Single compounds good attractants • Screening of several compounds by single sensillum recordings
  21. 21. Location of sensilla = Odor detecting sensory hairs
  22. 22. Single sensillum recording with odor stimuli
  23. 23. Stimulus: substance that activates neuron 1 sec 2 3 4 Single sensillum recording
  24. 24. Field trapping – plant odors • Strong attraction to 2,3-butanediol
  25. 25. Do sorghum chafers use pheromones?
  26. 26. Wire mesh cage with bait placed here Beetles Wire mesh cage Sex pheromone
  27. 27. Wire mesh cage with bait placed here Beetles Wire mesh cage Banana Aggregation pheromone
  28. 28. Field trapping – live insects Mean trap catch over four days 0 10 20 30 40 50 60 Unm.F Mated F M M+F Unm.F +Food M +Food M+F +Food Food Control males females Unmated females attract males
  29. 29. Field trapping – live insects Mean trap catch over four days 0 10 20 30 40 50 60 Unm.F Mated F M M+F Unm.F +Food M +Food M+F +Food Food Control males females Mated females or males are not attractive
  30. 30. Field trapping – live insects Mean trap catch over four days 0 10 20 30 40 50 60 Unm.F Mated F M M+F Unm.F +Food M +Food M+F +Food Food Control males females Combining unmated females with food increases attraction
  31. 31. Pheromone identification • Multiple extractions of males and females • Comparison of odor profiles
  32. 32. Pheromone identification • Multiple extractions of males and females • Comparison of odor profiles 19 female-unique compounds
  33. 33. Field trapping - female compounds
  34. 34. Field trapping - female compounds • Phenylacetaldehyde very attractive to both sexes
  35. 35. Future plans • Field testing of blends SUPERLURE! • Lures with high longevity • Cheap & efficient traps
  36. 36. Jonas Yitbarek Bekele Emiru Stefan Satya Gitachew Merid Gashebesaw & the field team Collaboration: Ministry of Agriculture, Addis Ababa Funding: Sida / SAREC

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