| Dates: |
April 1996 - March
2000 |
| Funding: |
DFID Crop Protection
Programme |
| Countries: |
Niger, West Africa |
| Collaborators: |
Dr Ousmane Youm, ICRISAT Sahelian
Centre, Niamey, Niger |
|
| NRI Project Leader: |
David
Hall |
Background
 |
Examining
millet in Niger |
| ©
University of Greenwich |
|
Millet is a major subsistence
food crop in the Sahelian region of West Africa, particularly
for household use by women. It is an important source
of fodder and building materials and can provide a source
of cash income for poorer households. Two insect pests,
the millet stem borer, Coniesta ignefusalis Hampson
(Lepidoptera: Pyralidae) and the millet head miner,
Heliocheilus albipunctella (de Joannis) (Lepidoptera:
Noctuidae), together cause annual yield losses estimated
at more than US$207 million and affect the livelihoods
of millions of the poorest people in Africa. In previous
collaborative work, the female sex pheromone of C.
ignefusalis was identified and and initial studies
carried out on its use in the field. This project investigated
the chemical ecology of the two pests in order to determine
the potential of pheromones and plant chemicals in their
management.
Results
In further work on mating disruption
of C. ignefusalis new controlled release dispensers
were developed which lasted for a whole millet season
in the field. In replicated trials on 0.5 ha plots in
farmers' fields during 1997 and 1998, these gave >99%
disruption of communication but had no consistently significant
effect on infestation or damage by C. ignefusalis.
Methods were established for
rearing H. albipunctella in the laboratory and
avoiding diapause for the first time. This made possible
a detailed study of the mating behaviour of this species
in laboratory and field. Earlier suggestions that female
moths are attracted to the males were confirmed conclusively.
The males make a buzzing sound and the characteristics
and mechanism of this were described in detail. Behavioural
studies indicated that the buzzing is the primary stimulus
for attraction, and the quality of the sound is critical.
No evidence for chemical stimuli was found in behavioural
bioassays, and no biologically active components were
found in male volatiles using GC-MS and GC-EAG. No trace
of diethyl malonate could be found, although this was
previously reported to be a potential pheromone component
in extracts of genitalia of male H. albipunctella.
Laboratory
studies showed a remarkable preference by female H.
albipunctella moths to oviposit on millet panicles
at 30% emergence over panicles at floral or grain-filling
stages, other parts of the millet plant or sorghum panicles.
Initial results indicated that methanolic extracts of
the panicles encouraged oviposition when applied to
filter papers, suggesting that chemical stimuli played
a major part in encouraging oviposition. Subsequent
attempts to repeat this work were less successful, although
significantly less oviposition occurred on panicles
after they had been extracted with hexane or methanol.
Other
results indicated that volatile chemicals from the millet
panicles play a part in encouraging oviposition. Analysis
of the composition of volatiles from millet panicles
at different stages of development and sorghum panicles
showed significant differences and highlighted nine
components that might be responsible for encouraging
oviposition on millet panicles at 30% emergence or for
discouraging oviposition on other stages.
A
new technique for assessing resistance/tolerance of
millet to H. albipunctella has been developed
by ICRISAT-SC and further refined. Two studies carried
out with farmers in Niger showed a low but significant
level of awareness of the link between insect numbers,
pest damage and yield loss. The ICRISAT damage rating
scale could be adapted to give farmers a reliable method
for estimating potential yield loss due to H. albipunctella
and hence the need for control measures.
Project
outputs included the holding of a "Regional Training
Workshop on the Use of Pheromone Technology in the Management
of Millet Stem Borer" in Niger and production of
a handbook in English and French. Materials were provided
for monitoring of C. ignefusalis with pheromone
traps in the 12 countries of the West and Central Africa
Millet Research Network (WCAMRN). The project produced
seven peer-reviewed papers, one Handbook and nine internal
reports presented as draft publications.
Uptake
A suitable formulation for use of the pheromone of C.
ignefusalis in mating disruption has been developed
and evaluated and it is proposed to develop this further
during a project in Niger, Nigeria and Burkina Faso
funded by IFAD. Project outputs have established there
is little prospect of using manipulation of mate-finding
behaviour in control of H. albipunctella. In
contrast, results on host finding and oviposition site
selection and by H. albipunctella should be followed
up with millet breeders. The marked preference for oviposition
sites by female H. albipunctella would be a good
target for use in development of resistant/tolerant
varieties of millet. The findings on chemical stimuli
for oviposition should be developed further and the
relative importance of chemical and physical stimuli
established. Farmer surveys confirmed H. albipunctella
is the most damaging insect pest of millet in the Sahel,
and development of resistant varieties appears to be
the most appropriate approach to management of this
pest by smallholder farmers in the Region.
Publications
YOUM, O., TOURE, K., DARBOE, M.,
RATNADASS, A., MAHAMADOU, C.I., BALDE, M. and HALL,
D.R. (1997) Monitoring pearl millet stem borer (Coniesta
ignefusalis (Hampson)) populations using pheromone-baited
traps. Part I: Results from Mali, Gambia, Niger and
Senegal. International Sorghum and Millets Newsletter,
No. 38, 134-136.
DAKOUO, YOUM, O., GWADI, W.K.,
AJAYI, O., DIKE, M.C., YEHOUENOU, A. and TANZUBIL, P.
(1997) Monitoring pearl millet stem borer (Coniesta
ignefusalis (Hampson)) populations using pheromone-baited
traps. Part II: Results from Benin, Burkina Faso, Ghana
and Nigeria. International Sorghum and Millets Newsletter,
No. 38, 137-138.
YOUM, O., BEEVOR, P.S., MCVEIGH,
L.J. and DIOP, A. (1997). Effect of trap height and
spacing in relation to crop height on catches of the
millet stemborer, Coniesta ignefusalis males. Insect
Science and its Application, 17:162-168.
YOUM, O., BEEVOR, P.S., HALL, D.R.
and MCVEIGH, L.J. (1997). The potential use of pheromones
for the management of the millet stemborer, Coniesta
ignefusalis (Hampson). Insect Science and its Application,
17:169-173.
YOUM, O., RUSSELL, D.A. and HALL,
D.R. (1998). Use of Pheromone Traps for Monitoring Millet
Stem Borer, C. ignefusalis. ICRISAT press. 20pp.
English and French versions
YOUM, O. and OWUSU, E. (1998) Farmers'
perceptions of crop losses due to insect pests and methods
for assessment in pearl millet. International Journal
of Pest Management 44: 123-125.
YOUM, O. and OWUSU, E. (1998) Assessment
of yield loss due to the millet head miner Heliocheilus
albipunctella (Lepidoptera: Noctuidae) using a damage
rating scale and regression analysis in Niger. International
Journal of Pest Management 44: 119-121.
BEEVOR, P.S., YOUM, O., HALL, D.R.
and CORK, A. (1999) Identification and field evaluation
of components of the female sex pheromone of the millet
stem borer, Coniesta ignefusalis (Hampson) (Lepidoptera:
Pyralidae). Journal of Chemical Ecology, 25:
2643-2664. (Abstract
[PDF 62Kb])
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