Hover flies are efficient pollinators of oilseed rape

Abstract

Understanding the consequences of declining diversity and abundance of pollinators for crops and floral biodiversity is a major challenge for current conservation ecology. However, most studies on this issue focus on bees, while other invertebrate taxa are largely ignored. We investigated the pollination efficiency of the globally abundant hover fly Episyrphus balteatus on the common crop, oilseed rape (Brassica napus). The study was conducted over a period of 2 consecutive years by means of enclosure experiments at an agricultural site located in Central Hesse (Germany). E. balteatus significantly increased both seed set and yield. This effect was very constant in the 2 years, despite considerable interannual differences in total seed numbers and seed mass. It highlights the important role of hover flies as pollinators of arable crops under varying environmental conditions. In contrast to bees, the effect of E. balteatus was lower at high pollinator densities than at low pollinator densities. This suggests adverse effects of density-dependent factors on pollination efficiency at high densities. Thus, models ignoring the modulating effect of biotic interactions by generally assuming a simple positive relationship between pollinator density and pollination efficiency might not apply to a vital component of the pollinator community.

Non-bee insects are important contributors to global crop pollination

“…Wild bees are known to improve seed set, quality, shelf life, and commercial value of a variety of crops (13)(14)(15)(16)(17). Increasingly, studies indicate that insect pollinators other than bees, such as flies, beetles, moths, and butterflies, are equally if not more important for the production of some crops (18)(19)(20)(21)(22)(23)(24). Nonetheless, the contribution to crop pollination by non-bee insects has been largely unnoticed, with most global syntheses focusing on bees (25)(26)(27)(28) or grouping together all bee and non-bee wild-insect pollinators (11).…”

“…Non-bee taxa, in particular, often have broader temporal activity ranges (34)(35)(36) and can provide pollination services at different times of the day compared with bees and in weather conditions when bees are unable to forage (37)(38)(39)(40). In addition, non-bee taxa may be more efficient in transferring pollen for some crops under certain conditions (18,19,38) and/or carry pollen further distances than some bees (41). It has been suggested that this long-distance pollen transfer could have important genetic consequences for wild plants (42,43).…”

Survey of Soybean Insect Pollinators: Community Identification and Sampling Method Analysis

“…Adults of some syrphid species are documented pollinators of other mass flowering crops including greenhouse sweet peppers, Capsicum annuum L., oilseed rape, Brassica napus L., and almonds, Prunus dulcis (Miller) D.A. Webb (Jarlan et al 1997, Jauker and Wolters 2008, Klein et al 2012. The abundance of syrphids in Iowan soybean fields is considered a function of the predation by the larval stages on insect pests, like the soybean aphid, Aphis glycines Matsumura, (Hemiptera: Aphidiidae) (Schmidt et al 2008).…”

Pollinators diversity and their effects on rapeseed (Brassica campestris L. var. toria) production and productivity in Chitwan, Nepal

“…Simon Fraser University in British Columbia found that bee abundance was the greatest in canola fields that had more uncultivated land within 750 m of field edges and seed set was greater in fields with higher bee abundance (Morandin and Winston, 2006); this could be the reason for higher yield in semi-natural fields. Considerable yield in intensive agriculture was obtained in the condition of low population of bees which could be supported by the availability of dipterans population especially syrphid flies, because study has showed that some species of hover flies (Syrphidae) also significantly increased seed set and yield in canola (Jauker and Wolters, 2008).…”