Field Margin Vegetation in Tropical African Bean Systems Harbours Diverse Natural Enemies for Biological Pest Control in Adjacent Crops
by
Prisila A. Mkenda 1,2,*
, Patrick A. Ndakidemi 1, Philip C. Stevenson 3,4, Sarah E. J. Arnold 3, 
Steven R. Belmain 3, Maneno Chidege 5 and Geoff M. Gurr 6,7
Prisila A. Mkenda 1,2,*, Patrick A. Ndakidemi 1, Philip C. Stevenson 3,4, Sarah E. J. Arnold 3, Steven R. Belmain 3, Maneno Chidege 5 and Geoff M. Gurr 6,7
1
Department of Sustainable Agriculture, Biodiversity and Ecosystems Management, The Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha 23311, Tanzania
2
Department of biosciences, Sokoine University of Agriculture, P.O. Box 3000, Morogoro 67129, Tanzania
3
Natural Resources Institute, University of Greenwich, Chatham Maritime, Kent ME4 4TB, UK
4
Royal Botanic Gardens, Kew, Richmond Surrey TW9 3AB, UK
5
Department of Research, Plant Protection Division, Tropical Pesticide Research Institute (TPRI), P.O. Box 3024, Arusha 23201, Tanzania
6
Graham Centre for Agricultural Innovation, Charles Sturt University, P.O. Box 883, Orange, NSW 2800, Australia
7
Institute of Applied Ecology, Fujian Agriculture and Forestry University, Fuzhou 350002, China
*
Author to whom correspondence should be addressed.
Sustainability 2019, 11(22), 6399; https://doi.org/10.3390/su11226399
Received: 24 September 2019 / Revised: 17 October 2019 / Accepted: 19 October 2019 / Published: 14 November 2019
Non-crop vegetation around farmland can be valuable habitats for enhancing ecosystem services but little is known of the importance of field margins in supporting natural enemies of insect pests in tropical agriculture. This study was conducted in smallholder bean fields in three elevation zones to assess the importance of field margin vegetation to natural enemy populations and movement to the bean crop for biological pest control. The pests and natural enemies were assessed using different coloured water pan traps (to ensure the capture of insects with different colour preferences) and the interactions of the two arthropod groups with the margin vegetation and their movement to the bean crop were monitored using fluorescent dye. Sentinel plants were used to assess predation and parasitism levels. A total of 5003 natural enemies were captured, more in the field margin than within the bean field for low and mid elevation zones, while in the high elevation zone, they were more abundant within the bean field. Pests were more abundant in the crop than margins for all the elevation zones. The use of a dye applied to margin vegetation demonstrated that common natural enemy taxa moved to the crop during the days after dye application. The proportion of dye-marked natural enemies (showing their origin to be margin vegetation) sampled from the crop suggest high levels of spatial flux in the arthropod assemblage. Aphid mortality rates (measured by prey removal and parasitism levels on sentinel plants) did not differ between the field edges and field centre in any of the three elevation zones, suggesting that for this pest taxon, the centre of the fields still receive comparable pest control service as in the field edges. This study found that field margins around smallholder bean fields are useful habitats to large numbers of natural enemy taxa that move to adjacent crops providing biological pest control service.
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Keywords:
ecosystem service; pest regulation; predators; parasitoids; non-crop vegetation
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MDPI and ACS Style
Mkenda, P.A.; Ndakidemi, P.A.; Stevenson, P.C.; Arnold, S.E.J.; Belmain, S.R.; Chidege, M.; Gurr, G.M. Field Margin Vegetation in Tropical African Bean Systems Harbours Diverse Natural Enemies for Biological Pest Control in Adjacent Crops. Sustainability 2019, 11, 6399.
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