title: Experimental evidence that honeybees depress wild insect densities in a flowering crop.
abstract: While addition of managed honeybees (Apis mellifera) improves pollination of many entomophilous crops, it is unknown if it simultaneously suppresses the densities of wild insects through competition. To investigate this, we added 624 honeybee hives to 23 fields of oilseed rape (Brassica napus L.) over 2 years and made sure that the areas around 21 other fields were free from honeybee hives. We demonstrate that honeybee addition depresses the densities of wild insects (bumblebees, solitary bees, hoverflies, marchflies, other flies, and other flying and flower-visiting insects) even in a massive flower resource such as oilseed rape. The effect was independent of the complexity of the surrounding landscape, but increased with the size of the crop field, which suggests that the effect was caused by spatial displacement of wild insects. Our results have potential implications both for the pollination of crops (if displacement of wild pollinators offsets benefits achieved by adding honeybees) and for conservation of wild insects (if displacement results in negative fitness consequences).
authors.affiliation: Department of Ecology, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden sandra.lindstrom@hushallningssallskapet.se.|Swedish Rural Economy and Agricultural Society, 291 09 Kristianstad, Sweden.|Department of Biology, Lund University, 223 62 Lund, Sweden.
authors.forename: Sandra A M
authors.identifier: 0000-0002-8403-3509
authors.initials: SA
authors.lastname: Lindström
authors.affiliation: Centre for Environmental and Climate Research, Lund University, 223 62 Lund, Sweden.
authors.forename: Lina
authors.initials: L
authors.lastname: Herbertsson
authors.affiliation: Department of Biology, Lund University, 223 62 Lund, Sweden.
authors.forename: Maj
authors.initials: M
authors.lastname: Rundlöf
authors.affiliation: Department of Ecology, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Bommarco
authors.affiliation: Department of Biology, Lund University, 223 62 Lund, Sweden.|Centre for Environmental and Climate Research, Lund University, 223 62 Lund, Sweden.
authors.forename: Henrik G
authors.initials: HG
authors.lastname: Smith
mesh_terms: D000383:Agriculture / Q000379:methods; D000818:Animals; D001516:Bees; D029688:Brassica napus; D018556:Crops, Agricultural; D035264:Flowers; D007313:Insecta; D054817:Pollination; D011157:Population Dynamics
keywords: crop pollinators; flies; interspecific competition; oilseed rape; wild bees