Insect pollination is important in a smallholder bean farming system

Abstract

Background Many crops are dependent on pollination by insects. Habitat management in agricultural landscapes can support pollinator services and even augment crop production. Common bean (Phaseolus vulgaris L.) is an important legume for the livelihoods of smallholder farmers in many low-income countries, particularly so in East Africa. While this crop is autogamous, it is frequently visited by pollinating insects that could improve yields. However, the value of pollination services to common beans (Kariasii) yield is not known. Methods We carried out pollinator-exclusion experiments to determine the contribution of insect pollinators to bean yields. We also carried out a fluorescent-dye experiment to evaluate the role of field margins as refuge for flower-visitors. Results Significantly higher yields, based on pods per plant and seeds per pod, were recorded from open-pollinated and hand-pollinated flowers compared to plants from which pollinators had been excluded indicating that flower visitors contribute significantly to bean yields. Similarly, open and hand-pollinated plants recorded the highest mean seed weight. Extrapolation of yield data to field scale indicated a potential increase per hectare from 681 kg in self-pollinated beans to 1,478 kg in open-pollinated beans indicating that flower visitors contributed significantly to crop yield of beans. Our marking study indicated that flower-visiting insects including bees, flies and lepidopterans moved from the field margin flowers into the bean crop. Overall, these results show that insect pollinators are important for optimising bean yields and an important food security consideration on smallholder farms. Field margin vegetation also provides habitat for flower-visiting insects that pollinate beans. Hence, non-crop habitats merit further research focusing on establishing which field margin species are most important and their capacity to support other ecosystem services such as natural pest regulation or even pests.

Beneficial insects are associated with botanically rich margins with trees on small farms

“…Fields were selected from four agro-ecological zones (agriculturally intense mid-elevation in Bunda, Malawi; low elevation zone, Tanzania (< 1000 m); mid elevation zone, Tanzania (1000–1500 m); high elevation zone, Tanzania (> 1500 m)). The three zones in Tanzania represented a gradient of climates and growing conditions 44 but were all of tropical highland climate with annual rainfall of 600 to 2000 mm (increasing with elevation) and a bimodal rainfall peak 10 . The Malawian zone was of subtropical highland climate with annual rainfall of 700 mm concentrated in a unimodal peak.…”

“…In sub-Saharan Africa, however, there is less evidence that beneficial insects move from the margin into the crop 10 . While positive impacts of non-crop vegetation have been observed for pollinators 11 and natural enemies 12 , other studies found no such impacts 13 .…”

“…We evaluated the relationship between botanical diversity in and around common bean ( Phaseolus vulgaris L.) fields and invertebrate abundance and activity in smallholder agroecosystems. Common beans are a key protein source for smallholder farmers in this region, and insect pollination provides measurable yield benefits 10 , 26 , so optimising beneficial insects has considerable potential for livelihood improvement. The crop is mainly considered to be pollinated in African agricultural landscapes by honeybees ( Apis mellifera ) and wild carpenter bees ( Xylocopa spp.)…”

Balancing Bees and Livestock: Pastoralist Knowledge, Perceptions and Implications for Pollinator Conservation in Rangelands, Northern Tanzania

“…This is similar to findings with (Winfree, 2010) who found bee abundance and species richness to be negatively affected by habitat fragmentation. As most Maasai are currently agro-pastoralists, harnessing pollinator benefits like pest control from Coccinellidae beetles (Mkenda et al, 2020) and pollination to boost crop yields will contribute towards conservation as has been shown in (Elisante et al, 2020;Klein et al, 2007). With the exclusion of natural disasters such as climate change and drought, there is need to create awareness about the human disturbances that promote pollinator declines, especially in pastoralist communities.…”

An Innate Preference of Bumblebees for Volatile Organic Compounds Emitted by Phaseolus vulgaris Plants Infected With Three Different Viruses

“…Phaseolus vulgaris L. (common bean) is a plant that benefits from insect pollination with increased seed production (Ibarra-Perez et al, 1999;Kingha et al, 2012;Ramos et al, 2018;Elisante et al, 2020) and is also host to a number of viruses that can reduce seed yield. Bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV) are closely related potyviruses that are among the most prevalent viruses infecting legumes and both result in serious crop loss (Morales, 2006).…”