Field Margin Plants Support Natural Enemies in Sub-Saharan Africa Smallholder Common Bean Farming Systems

Abstract

Flower-rich field margins provide habitats and food resources for natural enemies of pests (NEs), but their potential, particularly in the tropics and on smallholder farms, is poorly understood. We surveyed field margins for plant-NE interactions in bean fields. NEs most often interacted with Bidens pilosa (15.4% of all interactions) and Euphorbia heterophylla (11.3% of all interactions). In cage trials with an aphid-infested bean plant and a single flowering margin plant, the survival of Aphidius colemani, the most abundant parasitoid NE in bean fields, was greater in the presence of Euphorbia heterophylla than Bidens pilosa, Tagetes minuta, and Hyptis suaveolens. UV-fluorescent dye was applied to flowers of specific field margin plant species and NE sampled from within the bean crop and field margins using sweep-netting and pan-traps respectively. Captured insects were examined for the presence of the dye, indicative of a prior visit to the margin. Lady beetles and assassin bugs were most abundant in plots with B. pilosa margins; hoverflies with T. minuta and Parthenium hysterophorus margins; and lacewings with T. minuta and B. pilosa margins. Overall, NE benefitted from field margin plants, and those possessing extra floral nectaries had an added advantage. Field margin plants need careful selection to ensure benefits to different NE groups.

Plant-Rich Field Margins Influence Natural Predators of Aphids More Than Intercropping in Common Bean

“…This field trial was carried out in Kwa Sadala Village in the Hai District, Kilimanjaro Region, Tanzania (3°10′0″ S, 37°10′0″ E). Thirty-two sites ≥0.20 ha with either high (n = 16) or low (n = 16) plant diversity were selected based on the observed number of plant species in non-crop vegetation around each farm [ 50 ]. To quantify the diversity of the plant species in our field sites, the Shannon index (H′) [ 51 ] was used according to the formula below to calculate low diversity fields (H′ = 1.2) and high diversity fields (H′ = 2.3).…”

Using Block Kriging as a Spatial Smooth Interpolator to Address Missing Values and Reduce Variability in Maize Field Yield Data

“…In addition, the harvest of plants grown in the central rows of the field plots is also used because the plants of these rows are considered more representative than the plants from guard rows (edge or marginal plants) that are less affected by the competition of nearby plants, and thus become more productive but less appropriate for representative sampling [7,8]. In general, the number of margin plants or the width of the crop field margin used in agronomical research experiments can vary due to the specific experiment and its objectives; in particular, in some experiments, margin plants are not used at all, while in others, a specific number of plants or a crop field margin may be used to control various factors and minimize experimental error [9,10]. It seems that there is no golden rule to this and usually only a narrow width zone is considered a margin.…”

“…It seems that there is no golden rule to this and usually only a narrow width zone is considered a margin. For example, in a four-treatment plot experiment [9], a field margin of only 0.5 m was used in the plots with dimensions of 15 × 15 m. In another study [10], the crop edge was defined as the outer only few meters of the crop, which may be part of a nature conservation strip in a conservation headland or an unsprayed crop edge, or otherwise, even a conventional crop. In the case of large areas that crop fields occupy, a field margin with a width of 3 to 10 m (median) is recommended from the farmers' point of view [11], which can also be considered as narrow in width compared to the total crop area.…”

Advances in Alternative Measures in Plant Protection

“…When it comes to the natural regulation of pests, it is particularly important to provide suitable conditions for beneficial organisms. Field margin plant species are considered to be food and shelter for specific pests; therefore, it is crucial to study the biology of the host plants and how they interact with pests [ 6 ].…”