Annual flower strips support pollinators and potentially enhance red clover seed yield

Abstract

Ecological intensification provides opportunity to increase agricultural productivity while minimizing negative environmental impacts, by supporting ecosystem services such as crop pollination and biological pest control. For this we need to develop targeted management solutions that provide critical resources to service‐providing organisms at the right time and place. We tested whether annual strips of early flowering phacelia Phacelia tanacetifolia support pollinators and natural enemies of seed weevils Protapion spp., by attracting and offering nectar and pollen before the crop flowers. This was expected to increase yield of red clover Trifolium pratense seed. We monitored insect pollinators, pests, natural enemies and seed yields in a total of 50 clover fields along a landscape heterogeneity gradient, over 2 years and across two regions in southern Sweden. About half of the fields were sown with flower strips of 125–2,000 m2. The clover fields were pollinated by 60% bumble bees Bombus spp. and 40% honey bees Apis mellifera. The clover seed yield was negatively associated with weevil density, but was unrelated to bee species richness and density. Flower strips enhanced bumble bees species richness in the clover fields, with the strongest influence in heterogeneous landscapes. There were few detectable differences between crop fields with and without flower strips. However, long‐tongued bumble bees were redistributed toward field interiors and during phacelia bloom honey bees toward field edges. Clover seed yield also increased with increasing size of the flower strip. We conclude that annual flower strips of early flower resources can support bumble bee species richness and, if sufficiently large, possibly also increase crop yields. However, clover seed yield was mainly limited by weevil infestation, which was not influenced by the annual flower strips. A future goal should be to design targeted measures for pest control.

Repellency of insecticides and the effect of thiacloprid on bumble bee colony development in red clover (Trifolium pratense L.) seed crops

“…Bumble bee species were only identified in Vestfold in 2013 (Experiment 1). The high number of species within the Bombus terrestris group found in this crop (83% of the individuals registered) is in accordance with other studies, both in red clover (Havstad et al 2015) and other crops/landscape types in SE Norway (Ødegaard et al 2009, Wermuth and Dupont 2010, Rundlöf et al 2018. As this short-tonged species often bites a hole at the lower end of the corolla to get access to the nectar, its efficacy as red clover pollinator is debatable (e.g.…”

Factors Underlying Seed Yield in Red Clover: Review of Current Knowledge and Perspectives

“…Also, when few alternative pollen and nectar sources are available, honeybees are observed as pollinators on red clover [12,24,33,34]. To conclude, honeybees are the main pollinators of red clover in warm climates such as Serbia [13], while bumblebees prevail in temperate climates such as Belgium [35] and in Nordic regions such as Denmark and Sweden [12,36]. Leafcutter bees (Megachile rotundata Fab.)…”

Annual Wildflower Strips as a Tool for Enhancing Functional Biodiversity in Rye Fields in an Organic Cultivation System

“…Several studies have investigated the effects of annual WFSs on crop field biodiversity in Europe, e.g., in maize in Germany [13], in cereals in Belgium [14], in melon crops in Spain [15] and in red clover in Sweden [16]. These studies show that establishing annual WFSs can be effective means for increasing both taxonomical and functional diversity of insects in crop fields.…”