Managing populations of bruchid pests in grain legumes: role of resource provisioning at field and landscape levels

Abstract: Bruchids (Coleoptera: Bruchidae) seriously affect the production of grain legumes in the world. By developing in the seeds, bruchids reduce seed weight, alter their germination
potential, and compromise their value for both human and animal consumption. To date, limited effective management strategies are available, and little is known about their ecology. In order to improve the management of bruchids, we investigated how local and landscape factors support their populations and those of their main natural enemies, such as a micro-hymenoptera parasitoid. Over two years, we conducted field observations in 80 fields, grown with lentil or faba bean, across four production basins in France. At the landscape scale, we found that the bruchid population density was positively related to proportional area of host crops (faba bean or lentil) cultivated in the preceding year, whereas larger host crop areas in the current year tended to mitigate infestation pressure, consistent with a dilution effect. Wooded areas also increased the bruchid populations in lentils (overwintering habitat), while hedges reduced them in faba beans. The provision of nectar resources within the field and on field edges increased slightly bruchids populations in faba bean fields. However, these resources also had a positive effect on the parasitism of bruchids. Agronomic practices at field level had no effect highlighting the need for concerted strategies at the landscape level to improve the management of bruchids populations and of their natural enemies.