Present address: European Biological Control Laboratory, USDA–ARS, CS 90013 Montferrier sur Lez, 34988 St Gely du Fesc, France.
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Teretrius nigrescens against larger grain borer Prostephanus truncatus in African maize stores: biological control at work?
Article first published online: 8 APR 2003
DOI: 10.1046/j.1365-2664.2003.00805.x
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How to Cite
Holst, N. and Meikle, W. G. (2003), Teretrius nigrescens against larger grain borer Prostephanus truncatus in African maize stores: biological control at work?. Journal of Applied Ecology, 40: 307–319. doi: 10.1046/j.1365-2664.2003.00805.x
Publication History
- Issue published online: 8 APR 2003
- Article first published online: 8 APR 2003
- Received 12 February 2002; final copy received 29 December 2002
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Keywords:
- integrated pest management;
- predator;
- prey;
- population dynamics;
- Sitophilus zeamais
Summary
- 1Following the accidental introduction of the bostrichid beetle Prostephanus truncatus into East and West Africa around 1980, a classical biological control campaign was launched in 1991; the histerid beetle Teretrius nigrescens was released as a biocontrol agent to prevent the destructive outbreak of the pest in small-farm maize stores. However, while the campaign has been ongoing, so has discussion in the scientific community about the merits of this campaign and its chances of success.
- 2From published and unpublished data from experimental maize stores in Benin, West Africa, we derived statistical models describing the in-store insect population dynamics, and were thus able to point out significant biological interactions and to explain the observed lack of biological control.
- 3We found that (i) T. nigrescens reduced significantly the population growth rate of both P. truncatus and the non-target pest, the weevil Sitophilus zeamais; (ii) T. nigrescens displayed a positive numerical response to both prey species, P. truncatus and S. zeamais; (iii) asymmetric competition existed between the two prey species, S. zeamais was negatively affected by P. truncatus but not vice versa; (iv) T. nigrescens and S. zeamais displayed negative intraspecific density-dependence whereas P. truncatus was resource-limited.
- 4We conclude that classical biological control with T. nigrescens is not likely to become successful, mainly due to the predator's intraspecific density-dependence and its low population growth rate compared with its prey. We recommend that further research on P. truncatus integrated pest management takes into account the farmer as an active agent managing the store.
- 5Synthesis and applications. When biocontrol does not result in satisfactory pest control, as in the case of P. truncatus, farmers should learn how to scout for the pest and take action when a need is detected. In areas where the pest is usually only a minor problem, the agricultural extension service should consider setting up a simple early warning system for their region. When attempts at classical biological control remain unsuccessful, as in the case of P. truncatus now for 10 years, policy-makers should prioritize training of extension service and farmers in integrated pest management techniques (e.g. need-based use of insecticides) as a necessary supplement to biocontrol.