Flies are important pollinators of mass-flowering caraway and respond to landscape and floral factors differently from honeybees

Marjaana Toivonen,Anna-Elina Karimaa,Irina Herzon,Mikko Kuussaari

doi:10.1016/j.agee.2021.107698

Marjaana Toivonen, Anna-Elina Karimaa + Show 2 more

Open Access

https://doi.org/10.1016/j.agee.2021.107698

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Abstract

Non-bee insects have been identified as important crop pollinators globally. However, strategies to protect pollinators and enhance crop pollination usually focus on supporting bees. This study examined the effects of landscape structure, location within field, and floral resources on pollinators’ visits on mass-flowering caraway (Carum carvi L.) in boreal farmland, and the effects of the visits on caraway yield. Pollinator visits on caraway flowers were monitored and caraway yield measured in 30 fields at landscapes ranging from field-dominated to forest-dominated landscapes. Hoverflies were the most abundant flower-visitors of caraway, followed by honeybees. Hoverflies and other flies made more flower visits on caraway than all bee species combined. Pollinator groups differed in their responses to landscape and local factors. Flies were most abundant near field edges and in landscapes with high forest cover. Non-syrphid flies and solitary bees responded positively to the cover of flowering herbs in the adjacent field margins. Flower visits by honeybees, instead, were positively related to the flowering crop cover in the study fields. Caraway seed yield increased with increasing number of flower visits by honeybees, hoverflies and all pollinators together. Pollinator exclusion reduced caraway fruit set (i.e. the number of fruits per flower) by 13% and seed yield by 40%. Our study is the first to report the high importance of flies to crop pollination in boreal farmland, where caraway is an important export crop. The results highlight the need of taking flies and their habitat requirements into account when developing strategies to enhance crop pollination.

Highlights

Pollinators play a vital role in natural and managed ecosystems by facilitating plant reproduction, and contributing to biodiversity, ecosystem stability, agricultural production and human well-being (Potts et al, 2016)
The most frequent visitors were hoverflies that made 36% of all flower visits. They were followed by honeybees and non-syrphid flies, with 25% and 20% of the flower visits, respectively
The total number of flower visits by all flies was higher than that by all bees, which was due to the high number of fly individuals (Table S1)

Summary

Introduction

Pollinators play a vital role in natural and managed ecosystems by facilitating plant reproduction, and contributing to biodiversity, ecosystem stability, agricultural production and human well-being (Potts et al, 2016). The implementation of these approaches is hampered by the lack of knowledge on the actual pollinator limitation of the cur rent crop production (but see Fijen et al, 2020; Reilly et al, 2020), and uncertainty about ecological and agronomic outcomes across a range of crops and regions (Dicks et al, 2016; Kovács-Hostyánszki et al, 2017; Kleijn et al, 2019). Due to complementary resource use among pollinator taxa, increased pollinator diversity can enhance and stabilize crop pollination (Blüthgen and Klein, 2011; Garibaldi et al, 2013, 2015)

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