Chemical Ecology for Sustainable Production of Sorghum in EthiopiaYlva Hillbur, Department of Plant Protection Biology, SLU

ABSTRACT: The sorghum chafer can cause devastating damage in ripening sorghum. The chafer is arelatively large (2.5 cm) scarab beetle and twenty or more of them can be found on each sorghumhead sucking out kernels in the milky stage. In dry-land parts of Ethiopia, where sorghum is animportant 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 famershave instead developed an alternative method using rotting fruit to attract beetles to a point source ofinsecticide. 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. Asynthetic, standardized attractant would allow for constant use as well as for monitoring of beetlepopulations between regions and seasons. In a joint project between SLU and Addis Ababa Universitywe have studied the biology and chemical ecology of the sorghum chafer and identified two highlyactive odor attractants. One is a host plant component discovered by electrophysiological screening ofthe antennal response to a wide range of known fruit and flower volatiles. The other is a pheromonecomponent identified from extracts of the sorghum chafer females. Both compounds catch largenumbers 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 questionsconcerned how many insect traps a farmer would need in order to catch enough beetle pests to beeffective, and what would the cost be. The project is starting to study this element now and next yearbut the effectiveness depends partly on the life cycle of the pest and the timing of the trapping. It thetraps can be produced cheaply enough it is anticipated that it could prove cost-effective.

Chemical ecology for sustainable production of sorghum in Ethiopia

Ylva Hillbur, Department of Plant Protection Biology, SLU

70% crop loss, difficult to control

Sorghum chafer, Pachnoda interrupta

Fruit can be scarceVariable bait quality

Objectives:

1.Standardize the traps with synthetic plant odor lure as bait

2. Increase efficiency by adding pheromones

Different food sources – which odor signals?

Sorghum bicolor Abutilon figarianum

Odor collection

Which odor molecules do the samples contain?

Gas chromatography (GC)

GC-EAD (GC-coupled Electro Antennographic Detection)

Which odor molecules can the insect smell?

GC-EAD using beetle antennae

Antennal response to sorghum odor

1.Tridecane 2.(Z)-3-Hexenol 3.1-Octen-3-ol 4.1-Octanol

Antennal response to abutilon odor

1.(Z)-3-Hexenol 2.Tetradecane 3.Methyl salicylate 4.Methyl anthranilate

Field testing

Rasa

Embuay Bad

Field Sites

Field trapping

Wire mesh cage with bait placed here

Beetles

Wire meshcage

Sex pheromone

The trap

Odor bait

The sorghum blend: as good as its’ best component

The abutilon blend: as good as its’ best component

• Single compounds good attractants

• Screening of several compounds by single sensillum recordings

Locationof sensilla=Odor detectingsensory hairs

Single sensillum recordingwith odor stimuli

Stimulus: substance that activates neuron

1 sec 2 3 4

Single sensillum recording

Field trapping – plant odors

• Strong attraction to 2,3-butanediol

Do sorghum chafers use pheromones?

Wire mesh cage with bait placed here

Beetles

Wire meshcage

Sex pheromone

Wire mesh cage with bait placed here

Beetles

Wire meshcage

Banana

Aggregation pheromone

Field trapping – live insectsMean 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

malesfemales

Unmated females attract males

Field trapping – live insectsMean 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

malesfemales

Mated females or malesare not attractive

Field trapping – live insectsMean 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

malesfemales

Combining unmated females with

food increasesattraction

Pheromone identification

• Multiple extractions of males and females

• Comparison of odor profiles

Pheromone identification

• Multiple extractions of males and females

• Comparison of odor profiles

19 female-unique compounds

Field trapping -female compounds

Field trapping -female compounds

• Phenylacetaldehyde very attractive to both sexes

Future plans

• Field testing of blends SUPERLURE!• Lures with high longevity• Cheap & efficient traps

Jonas Yitbarek Bekele Emiru Stefan Satya Gitachew Merid

Gashebesaw & the field team

Collaboration: Ministry of Agriculture, Addis AbabaFunding: Sida / SAREC