Pollination efficiency of wild bees and hoverflies provided to oilseed rape

Abstract

1 Declining numbers in honeybees and various wild bee species pose a threat to global pollination services. The identification and quantification of the pollination service provided by different taxa within the pollinator guild is a prerequisite for the successful establishment of nature conservation and crop management regimes. 2 Wild bees and hoverflies are considered to be valuable pollinators in agricultural and natural systems. Although some information on pollination efficiency of individual pollinator species is available, comparative studies of both taxa at different densities are rare. In the present study, the efficiency of the solitary mason bee Osmia rufa and two hoverfly species (Eristalis tenax and Episyrphus balteatus) as pollinators of oilseed rape Brassica napus was examined in a standardized caged plant breeding regime. Honeybee Apis mellifera colonies were used as a reference pollinator taxon. 3 Yield parameters responded differently to pollinator density and identity. Fruit set and number of seeds per pod increased with increasing pollinator density, although these were stronger in the mason bee than the hoverfly treatment. Weight per 1000 seeds did not respond to any pollinator treatment, indicating that seed quality was not affected. Oilseed rape yield in the highest tested densities of both pollinator taxa resulted in yield values close to the efficiency of small honeybee colonies. 4 Hoverflies required approximately five-fold densities of the red mason bees to reach a similar fruit set and yield. Thus, mason bees are more efficient in plant breeding and managed pollination systems. Both natural pollinator taxa, however, are of potential value in open and closed crop production systems.

Bee diversity effects on pollination depend on functional complementarity and niche shifts

“…In our experiment, hoverflies contributed only little to pollination, despite similar number of flower visits and higher number of individuals compared to bees. Low pollination effectiveness of hoverflies compared to bees is consistent with previous studies (e.g., Jauker et al 2012), questioning how far they can offset loss of pollination by bees.…”

Comparative study of the floral biology and of the response of productivity to insect visitation in two rapeseed cultivars (Brassica napus L.) in Rio Grande do Sul

“…For example, Mussury and Fernandes (2000) observed that pollination may occur during pre-anthesis, as flowers already presented dehiscent anthers at this time. Several studies have shown that even without visitation by pollinators, there is formation of siliques and seeds (Adegas and Nogueira Couto, 1992;Bommarco et al, 2012); nevertheless, as mentioned above and also shown in the present study, production is increased when insect pollination occurs (Adegas and Nogueira Couto, 1992;Durán et al, 2010;Rosa et al, 2011;Bommarco et al, 2012;Jauker et al, 2012). However, the positive effects on seed production and quality may vary between cultivars and plantation sites, as differences in the number of seeds per silique and seed weight were found between the study sites (see Figures 1 to 6).…”

“…When the two sites where the same cultivar (Hyola 61) was grown were compared, it was observed that seed weight was higher at Estrela under the autogamy treatment and at Guarani das Missões under the free visitation and xenogamy treatments. One hypothesis to explain this difference is that the amount of flower visitation is lower at Estrela than at Guarani das Missões, being insufficient to increase productivity and the quality of seeds to a level above the autogamy treatment, given that the pollinator density affects fruit production (Jauker et al, 2012). Another possible cause for this difference may be the composition of the pollinator community of each area, because the efficiency of pollinators varies with species (Ali et al, 2011).…”

Crop flower visitation by honeybees, bumblebees and solitary bees: Behavioural differences and diversity responses to landscape

“…One potential mechanism to further increase yield is to promote improved pollination by insects (Hayter and Cresswell, 2006;Bommarco et al, 2012;Jauker et al, 2012). Although oilseed rape is predominantly wind pollinated (Chifflet et al, 2011), the role of domesticated and wild insect pollinators in promoting pollination is potentially economically significant (Breeze et al, 2011;Chifflet et al, 2011;Bommarco et al, 2012;Jauker et al, 2012;Ollerton et al, 2012).…”

“…Although oilseed rape is predominantly wind pollinated (Chifflet et al, 2011), the role of domesticated and wild insect pollinators in promoting pollination is potentially economically significant (Breeze et al, 2011;Chifflet et al, 2011;Bommarco et al, 2012;Jauker et al, 2012;Ollerton et al, 2012). For example, increased insect pollination rates have been shown to raise oilseed rape yields, reduced chlorophyll content and positively impact on oil content and seed weight (Bommarco et al, 2012).…”