Ecology and management of crop pollination and pest control
Sammanfattning: The agricultural landscape has gone through large changes to meet increasing demands for food. This has led to major biodiversity declines, while effects on ecosystem services that support agricultural productivity, such as pollination and pest control, remain less studied. This thesis examines temporal trends, impacts, and management for functionally important insects in agriculture using red clover seed production as a model system. Red clover is pollinated by bumble bees (Bombus spp.) and honey bees. Major yield losses are caused by seed weevils (Apion spp.), which in turn are attacked by natural enemy parasitoids. Field studies, where sites previously sampled in the 1930s-1960s were revisited 2008-2011, showed a shift towards more species poor bumble bee communities in red clover fields dominated by a few species which are less effective pollinators. Moreover, crop pest damage by seed weevils had more than doubled, while parasitism rates provided by natural enemies had decreased. In parallel to these changes, seed yields have declined and become more variable in recent decades. We performed an experiment which showed that the gain in seed set obtained when simultaneously increasing pollination and pest control outweighed the sum of seed set gains obtained when increasing each service separately. With the field data collected we also developed integrated pest management by validating a pest sampling method, developing a threshold for insecticide treatment, and suggesting minimum effective chemical pest control. We further found that pest damage was higher in landscapes with a high proportion of agricultural land, and that maximising the distance to a clover field in the previous year could function as a proactive method to decrease pest abundance. In summary, this thesis shows that agricultural intensification can jeopardise the supply of crop pollination and pest control services, and that such changes may translate into crop yield effects. It further highlights that interactions between pollination and pest control can alter the benefits obtained from serviceproviding organisms, and this needs to be considered to properly manage multiple ecosystem services. Simultaneous enhancement of beneficial organisms which contribute to crop productivity and integrated management of pests that pose a threat to production can contribute to sustainable food production in agriculture.
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