Abstract
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.
Highlights
Natural pest regulation by beneficial arthropods can be enhanced through habitat management close to and within the crop [1,2] or at the landscape level [3,4], an approach known as conservation biological control [5]
Margin vegetation around the smallholder bean fields in this tropical system plays a significant role oMf ahragribnovuerignegtantiaotnuraarloeunnedmtihees tshmaatlmlhoovldeeirnbtoeathnefifieeldlds cinrotphitsoteroxperict abliosylosgteicmalpplaeystscaosnitgrnoli.fiTcahnist rcoolnecolufshioanrbiosuinringgenneartaulraaglreeneemmeinetswthitaht omthovererienptoorttheedfsietulddicersotphatot nexoenr-tcrboipolovgegiceatlatpieosnt acroenatsroalr.oTuhnids conclusion is in general agreement with other reported studies that non-crop vegetation areas around agricultural fields in other types of systems provide habitats for natural enemy populations [10,41,42]
Natural enemies were found to move from the non-crop vegetation into the bean crops quickly and there was strong evidence of penetration to the centre of fields
Summary
Natural pest regulation by beneficial arthropods can be enhanced through habitat management close to and within the crop [1,2] or at the landscape level [3,4], an approach known as conservation biological control [5]. Together with non-crop vegetation along the field margin, contribute significantly to the abundance and diversity of the natural enemies within the crop land [11,12,13]. This is due to the fact that natural and semi-natural habitats are less disturbed in comparison to crop land. González et al [14] found that natural enemies moved from native forest to the crop to a greater extent than did herbivores
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