The sorghum chafer causes up to 70% crop loss in Ethiopia, but conventional control methods are ineffective; through chemical ecology research, the document identifies two highly attractive odor lures - a host plant component and female-produced pheromone - that could be developed into standardized lures to efficiently trap the pest and help farmers sustainably produce sorghum. Field tests found that combining an unmated female with food further increased trap catches, and a particular female-produced compound, phenylacetaldehyde, was very attractive to both sexes.

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. Chemical ecology for sustainable production of
sorghum in Ethiopia
Ylva Hillbur, Department of Plant Protection Biology, SLU

3. 70% crop loss, difficult to control

4. Sorghum chafer,
Pachnoda interrupta

6. Fruit can be scarce
Variable bait quality

7. Objectives:
1.Standardize the traps with synthetic plant
odor lure as bait
2. Increase efficiency by adding pheromones

8. Different food sources – which odor signals?
Sorghum bicolor Abutilon figarianum

9. Odor collection

10. Which odor molecules do the
samples contain?
Gas chromatography (GC)

11. GC-EAD
(GC-coupled Electro Antennographic Detection)
Which odor molecules can the
insect smell?

12. GC-EAD using beetle antennae

13. Antennal response to
sorghum odor
1.Tridecane 2.(Z)-3-Hexenol
3.1-Octen-3-ol 4.1-Octanol

14. Antennal response to abutilon odor
1.(Z)-3-Hexenol 2.Tetradecane
3.Methyl salicylate 4.Methyl anthranilate

15. Field testing

16. Rasa
Embuay Bad
Field Sites

17. Field trapping

20. Wire mesh cage
with bait placed here
Beetles
Wire mesh
cage
Sex pheromone
The trap
Odor bait

21. The sorghum blend:
as good as its’ best component

22. The abutilon blend:
as good as its’ best component

23. • Single compounds good attractants
• Screening of several compounds by
single sensillum recordings

24. Location
of sensilla
=
Odor detecting
sensory hairs

25. Single sensillum recording
with odor stimuli

26. Stimulus: substance that
activates neuron
1 sec 2 3 4
Single sensillum recording

27. Field trapping – plant odors
• Strong attraction to
2,3-butanediol

28. Do sorghum chafers use pheromones?

32. Wire mesh cage
with bait placed here
Beetles
Wire mesh
cage
Sex pheromone

33. Wire mesh cage
with bait placed here
Beetles
Wire mesh
cage
Banana
Aggregation pheromone

34. 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

35. 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

36. 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

37. Pheromone identification
• Multiple extractions of males and females
• Comparison of odor profiles

38. Pheromone identification
• Multiple extractions of males and females
• Comparison of odor profiles
19 female-unique compounds

39. Field trapping -
female compounds

40. Field trapping -
female compounds
• Phenylacetaldehyde very
attractive to both sexes

41. Future plans
• Field testing of blends SUPERLURE!
• Lures with high longevity
• Cheap & efficient traps

42. Jonas Yitbarek Bekele Emiru Stefan Satya Gitachew Merid
Gashebesaw & the field team
Collaboration: Ministry of Agriculture, Addis Ababa
Funding: Sida / SAREC