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Agricultural intensification has led to structurally simplified landscapes with reduced and fragmented resources for farmland insects. However, studies on the effects of landscape composition on farmland insects have mainly been performed in areas dominated by open arable land and semi-natural grasslands, while studies from forest-dominated landscapes are scarce. This research examined the effects of landscape composition on hoverfly species richness and abundance in arable land in boreal forest-dominated landscapes. Hoverflies were sampled in 22 mass-flowering caraway (Carum carvi) fields in Central Finland using pan traps. The effects of landscape composition on species richness and abundance were examined for all hoverflies, and for species groups with different adult habitat preferences. Landscape composition was measured as proportions of land cover classes within two different radii. Species richness and abundances of all hoverflies, forest species and open-habitat species increased with decreasing arable land cover and/or increasing forest cover within a 500 m radius (the two land cover classes strongly negatively correlated). Wetland species were most abundant in landscapes with an intermediate cover of arable land and forest, and most species-rich in landscapes with intermediate (10%) water cover. The species richness and abundance of mixed-habitat species increased with increasing cover of transitional woodland. Implications for insect conservation Our results show that most hoverfies in arable land benefit from increasing surrounding forest cover even in relatively heterogeneous, forest-dominated landscapes. Preserving or increasing the area of forests and other non-arable habitats is needed to safeguard a diversity of resources for hoverflies, and associated ecosystem services in farmland. Agricultural intensification has led to structurally simplified landscapes with reduced and fragmented resources for farmland insects. However, studies on the effects of landscape composition on farmland insects have mainly been performed in areas dominated by open arable land and semi-natural grasslands, while studies from forest-dominated landscapes are scarce. This research examined the effects of landscape composition on hoverfly species richness and abundance in arable land in boreal forest-dominated landscapes. Hoverflies were sampled in 22 mass-flowering caraway (Carum carvi) fields in Central Finland using pan traps. The effects of landscape composition on species richness and abundance were examined for all hoverflies, and for species groups with different adult habitat preferences. Landscape composition was measured as proportions of land cover classes within two different radii. Species richness and abundances of all hoverflies, forest species and open-habitat species increased with decreasing arable land cover and/or increasing forest cover within a 500 m radius (the two land cover classes strongly negatively correlated). Wetland species were most abundant in landscapes with an intermediate cover of arable land and forest, and most species-rich in landscapes with intermediate (10%) water cover. The species richness and abundance of mixed-habitat species increased with increasing cover of transitional woodland. Implications for insect conservation Our results show that most hoverfies in arable land benefit from increasing surrounding forest cover even in relatively heterogeneous, forest-dominated landscapes. Preserving or increasing the area of forests and other non-arable habitats is needed to safeguard a diversity of resources for hoverflies, and associated ecosystem services in farmland.

Ecological intensification has been proposed as a strategy to mitigate the impacts of conventional intensive land use on pollinators and insect pollination. However, research has concentrated on the effects of land management on pollinator abundance and diversity, while studies directly measuring pollination services are still lacking for many crops and regions. This study examines the effects of landscape heterogeneity, pesticide use intensity and flowering time on insect pollination of turnip rape Brassica rapa ssp. oleifera, a major oil crop at high latitudes. The field experiment included monitoring pollinator visits on turnip rape flowers and measuring yield in 34 spring-sown turnip rape fields in Southern Finland. The fields were situated in two landscape types that differed in the cover of arable land and represented independent gradients of pesticide use intensity and flowering time. Based on flower visits and number of seeds per silique, turnip rape was best pollinated in fields with late flowering time. The result suggests a temporal mismatch between crop flowering and the availability of pollination service in early sown fields. The increase in flower visits during summer was steeper among fields with low than high pesticide use, possibly due to a faster colony growth of important bee pollinators. Pollinator community in turnip rape fields was more diverse in heterogeneous landscapes with less arable land than in homogeneous field-dominated landscapes, suggesting higher stability of pollination services in diverse landscapes. Total yield per plant was positively related to pesticide use intensity. The relationship between insect pollination and total yield was weakened by high compensation capacity of turnip rape, the plants producing more flowers under poor pollination.Synthesis and applications. Crop pollination can be enhanced by shifting sowing time to better match crop flowering to the peak availability of the most important pollinators. Reduced pesticide use may also enhance pollination services but can lead to the total yield reduction due to pests. This highlights the need for pollinator-friendly pest control methods to maintain turnip rape yields while conserving pollination services. Foreign Language AbstractTiivistelma Maatalouden ekologista tehostamista on esitetty strategiaksi, jonka avulla intensiivisen maankayton kielteisia vaikutuksia polyttajiin ja hyonteispolytykseen voidaan hillita. Tutkimukset maankayton vaikutuksista viljelykasvien hyonteispolytykseen kuitenkin puuttuvat yha monilta viljelykasveilta ja alueilta. Tama tutkimus tarkasteli maiseman monimuotoisuuden, torjunta-aineiden kayton ja kukinta-ajan vaikutusta rypsin hyonteispolytykseen. Peltokokeessa seurattiin polyttajien vierailuja rypsin kukilla ja mitattiin satoa 34 kevatrypsipellolla Uudellamaalla. Pellot sijaitsivat kahdessa maisematyypissa, joista toinen oli peltovaltainen ja toinen monimuotoisempi ja vahemman peltoa sisaltava. Lisaksi pellot erosivat toisistaan torjunta-aineiden kayton ja kukinta-ajan suhteen. Polyttajien kukkavierailut ja siementen maara per litu olivat korkeimmillaan myohaan kukkineilla rypsipelloilla, mika kertoo hyvasta polytyksesta. Tuloksen perusteella aikaisin kylvetyt rypsipellot saattavat kukkia liian aikaisin polyttajien saatavuuden nakokulmasta. Voimakkaimmin polyttajien maara lisaantyi kesan aikana niiden peltojen joukossa, joilla ei kaytetty torjunta-aineita. Mahdollinen selitys on, etta tarhamehilaisten ja kimalaisten yhdyskunnat kasvoivat nopeimmin naiden peltojen laheisyydessa. Polyttajien monimuotoisuus oli suurempi monimuotoisessa kuin peltovaltaisessa maisemassa, mika parantaa polytyspalvelun vakautta muuttuvissa olosuhteissa. Kokonaissato per kasvi nousi torjunta-aineiden kayton lisaantyessa. Hyonteispolytyksen ja sadon valista yhteytta heikensi rypsin hyva kompensaatiokyky, jonka ansiosta heikosti polyttyneet kasvit tuottivat enemman kukkia.Yhteenveto ja sovellukset. Viljelykasvin polytysta voi parantaa saatamalla kylvoaikaa siten, etta kasvin kukinta ajoittuu tarkeimpien polyttajien runsaushuippuun. Torjunta-aineiden kayton vahentaminen voi parantaa polytysta mutta laskea samaan aikaan satoa tuholaisten ja rikkakasvien lisaantymisen takia. Polyttajaystavallisten kasvinsuojelukeinojen kehittaminen on tarkeaa korkeiden rypsisatojen ja polytyspalveluiden sailymisen kannalta. Crop pollination can be enhanced by shifting sowing time to better match crop flowering to the peak availability of the most important pollinators. Reduced pesticide use may also enhance pollination services but can lead to the total yield reduction due to pests. This highlights the need for pollinator-friendly pest control methods to maintain turnip rape yields while conserving pollination services. peerReviewed

Uncultivated field margins are important refugia for pollinating insects in agricultural landscapes. However, the spill-over of pollination services from field margins to adjacent crops is poorly understood. This study (i) examined the effects of landscape heterogeneity on pollinator occurrence in permanent field margins and pollinator visitation to adjacent mass-flowering turnip rape (Brassica rapa ssp. oleifera) in boreal agricultural landscapes, and (ii) tested whether pollinator abundance and species richness in field margins predict abundance and species richness of crop visitors. Pollinators visiting the crop were more affected by landscape heterogeneity than pollinators in adjacent margins. Species richness, total abundance, and the abundance of syrphid flies visiting the crop increased with increasing landscape heterogeneity, whereas, in field margins, landscape heterogeneity had little effect on pollinators. In field-dominated homogeneous landscapes, wild pollinators rarely visited the crop even if they occurred in adjacent margins, whereas in heterogeneous landscapes, differences between the two habitats were smaller. Total pollinator abundance and species richness in field margins were poor predictors of pollinator visitation to adjacent crop. However, high abundances of honeybees and bumblebees in margins were related to high numbers of crop visitors from these taxa. Our results suggest that, while uncultivated field margins help pollinators persist in boreal agricultural landscapes, they do not always result in enhanced pollinator visitation to the adjacent crop. More studies quantifying pollination service delivery from semi-natural habitats to crops in different landscape settings will help develop management approaches to support crop pollination.