Engineering smallholder common bean cropping systems with flowering plants increases hoverfly population and crop yields

Yamikani Kaliwo¹Ellen Kumchenga¹Yolice L.B. Tembo¹Trust Kasambala Donga¹Vernon H. Kambambe¹Philip Charles Stevenson^2,3Steven R. Belmain^2*

• ¹Lilongwe University of Agriculture and Natural Resources, Lilongwe, Malawi
• ²Natural Resources Institute, University of Greenwich, Greenwich, United Kingdom
• ³Royal Botanic Gardens Kew, Richmond, United Kingdom

Bean aphids are a major constraint to bean production worldwide and are commonly managed through intensive pesticide use. In many farming systems, particularly where crop production is increasingly intensified, reliance on chemical control has reduced the use and the appreciation of agroecological pest management strategies, including conservation biological control. The widespread application of pesticides not only suppresses natural enemies of aphids but also contributes to broader declines in insect diversity, especially when combined with the loss of non-crop habitats that support beneficial insects. To address this, we assessed whether engineering bean crop habitats with flowering plants could enhance adult hoverfly populations and increase hoverfly larval abundance within bean fields. The potential of four flowering plant species (Galinsoga parviflora, Ocimum basilicum, Bidens pilosa and Ageratum conyzoides) grown around bean crops to attract hoverflies was evaluated. Bean crops surrounded by flowering plant species were able to reduce aphid numbers and damage by 51% compared to the control treatment which had no field margin. Bean fields surrounded by O. basilicum had the lowest aphid damage score (1.2) and highest bean yield (917 kg/ha). Overall, bean crops surrounded by flowering plant species yielded between 621 to 917 kg/ha, which was 22-42% higher than the untreated control (509 kg/ha). Such evidence may help support policies that promote agroecological practices instead of synthetic pesticides.