1) Maize is a major crop in Africa that is devastated by stemborer pests, which can cause up to 88% yield losses. 2) The study aimed to determine how stemborer egg deposition changes the volatile emissions of maize varieties and how these volatiles affect parasitoids. 3) Certain maize landraces were found to emit volatiles in response to eggs that attract parasitoids, representing a novel indirect defense trait that could be bred into other varieties to improve resistance.

1. P L A N T H E A LT H
International Centre of Insect Physiology and
Ecology (icipe)
P.O. Box 30772-00100, Nairobi, Kenya
Tel: +254 (20) 8632000. E-mail: icipe@icipe.org
www.icipe.org
New directions for improving crop resistance to insects
Logo 1 Logo 2 Logo 3
Amanuel Tamiru* , Toby Bruce, Christine Woodcock, Charles Midega, Mike Birkett, John Pickett & Zeyaur Khan
Email: atamiru@icipe.org
BEHAVIORAL STUDY
INTRODUCTION
Maize (Zea mays L.) is the major staple food and cash crop for millions
of people in sub-Saharan Africa
Stemborers are devastating pests of maize in the region causing yield
losses of up to ~ 88%
Exploiting egg-induced plant defense may lead to developing cost-
effective and environmentally benign approaches of stemborer control
appropriate to resource-poor African farmers
OBJECTIVES
To determine changes in the profile of volatiles emitted by diverse
maize cultivars in response to stemborer egg deposition
To determine effects of egg induced plant volatiles on the behaviour
of key egg and larval parasitoids
To identify biologically active components responsible for any
observed behavioural responses in the parasitoids
METHODS
RESULTS
BEHAVIORAL STUDY
IMPACT
We discovered novel defense trait on certain maize landraces that
could be bred into cereal cultivars with other favorable agronomic
characteristics, to provide better crop resistance against stemborer
attack
This will have huge impact on alleviation of hunger and poverty as
stemborers infest about 50% of the agricultural land in sub-Saharan
Africa, affecting lives of nearly 300 million people and causing yield
losses of ~$ 1.5 billion per annum
CONCLUSION
Early herbivore induces changes in the volatile profile of certain
maize landraces leading to attraction of key natural enemies
(parasitoids)
Indirect defense response, elicited by oviposition, may have
been lost in the commercial varieties tested
Considerable potential to improve crop defense by introgressing
the indirect defence traits from landraces into mainstream maize
cultivars
REFERENCES/FOOTNOTES
Tamiru A.,Khan Z.R. & Bruce T.J.A. (2015). New directions for
improving crop resistance to insects by breeding for egg induced
defence. Current Opinion in Insect Science 9:51–55
Tamiru A., Bruce T.J.A., Midega C.A.O., Woodcock C.M., Birkett M.A.,
Pickett J.A. & Khan Z.R. (2012). Oviposition induced volatile emissions
from African smallholder farmers’ maize varieties. Journal of Chemical
Ecology 38:231–234.
Tamiru A., Bruce, T.J.A., Woodcock C.M., Caulfield J.C., Midega
C.A.O. , Ogol C.K.P.O., Mayon P., Birkett M.A., Pickett J.A. & Khan Z.R.
(2011). Maize landraces recruit egg and larval parasitoids in response
to egg deposition by a herbivore. Ecology Letters 14: 1075–1083.
Headspace sampling
(collection of volatiles)
±
Bioassay (naturals)
GC linked
electrophysiology
Glass arm
Perspex olfactometer
Airflow in
GC & GC-MS Analysis
Identification &
quantification of bioactive
compounds
Bioassay
(synthetics)
a
a
a
a
b
b
a
a
b b a
a
0
1
2
3
4
5
6
C2101 H2034 WS505 PH4
with eggs
no eggs
solvent control
NOT attractedAttracted
Meantimespent
(Min.±SE)
a
a
a a
b b b
b
c
c
b
c
0
1
2
3
4
5
B3016 C2101 H2034 V2658
ATTRACTED to plants with eggs
Meantimespent
(Min.±SE)
NOT attracted to plants with eggs
Meantimespent
(Min.±SE)
GC-MS ANALYSIS
INDUCTION on plants with eggs
Signal(pA)
RT (min)
C2101with eggs
C2101 no eggs
DMNT (E)-caryophyllene TMTT
GC-EAG ANALYSIS
C-2101 with eggs
Retention time (Min.)
6 8 10 12 14 16 18 20
Peakheight(pA)
a
b
c
e
f
g
i j
RT (min)
C2101 with eggs