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 Leaders: 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

Pheromone trap for C. ignefusalis Heliocheilus male Male Heliocheilus buzzing © University of Greenwich

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)

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