It Is Not All about Being Sweet: Differences in Floral Traits and Insect Visitation among Hybrid Carrot Cultivars

Abstract

<jats:p>Cytoplasmically male-sterile (CMS) carrot cultivars suffer from low pollination rates. In this study, insect visitation varied more than eightfold between 17 CMS carrot cultivars in a field-based cultivar evaluation trial. The visitation rates of honey bees, nectar scarabs, muscoid flies, and wasps each significantly differed among these cultivars. No significant difference in visitation rates was observed among cultivars of different CMS type (brown-anther or petaloid) or flower colour, but cultivars of Berlicumer root type had significantly higher insect visitation rates than Nantes. Six cultivars were further compared in regard to selected umbel traits: as umbel diameter increased, so did the visitation of soldier beetles, while that of honey bees decreased. Finally, nectar of these six cultivars was analysed for sugar content, which revealed monosaccharides to be the most common sugars in all. There was high variation in the levels of sugars from individual umbellets but no significant difference in nectar sugar composition among cultivars, suggesting that nectar sugar composition is of minor importance regarding pollinator attraction to hybrid CMS carrot umbels.</jats:p>

Critical pollination chemistry: Specific sesquiterpene floral volatiles in carrot inhibit honey bee feeding

“…In agreement with previous studies (Gaffney et al ., 2020), we show that the sugar levels and composition in our samples varied greatly between individuals, but no significant difference between accessions was observed. Our results show that sugars, and thereby reward quality was not linked to the observed differences in bee attraction between the accessions.…”

“…In this study, we used a comprehensive approach to identify specific traits affecting honey bee attraction to parental accessions and open-pollinated carrot flowers. Considering the need for cross-pollination, only traits present in both male-sterile and fertile parent accessions, such as nectar and floral volatiles (but not pollen), were targeted (Gaffney et al ., 2020). The results from our initial field bioassays suggested that the carrot nectars were not only lacking in attraction but were in fact repelling bees from the feeders.…”

“…Thus, hybrid carrot represents a suitable model for investigating variables that negatively affect pollination success in honey bee pollinated cropping systems. The effects of colour and floral morphology have been studied for bee pollination of carrot, with inflorescence color and nectar sugar composition and concentration found not to differ significantly between hybrid lines (Gracie, 2011; Gaffney et al ., 2020). However, no comprehensive studies of the role of volatiles have been reported.…”

Critical Pollination Chemistry: Specific Sesquiterpene Floral Volatiles in Carrot Inhibit Honey Bee Feeding

“…Considering the need for cross-pollination, only traits present in both male sterile and fertile parent accessions, such as nectar and floral volatiles (but not pollen), were targeted. 57 The results from our initial field bioassays suggested that the carrot nectars were not only lacking in attraction but also were in fact repelling bees from the feeders. These observations guided us to develop a new laboratory bioassay protocol, based on the concept by Kessler et al, 71 in which we were able to evaluate the combined effect of odor and taste.…”

“…The effects of color and floral morphology have been studied for bee pollination of carrots, with inflorescence color and nectar sugar composition and concentration found not to differ significantly between hybrid lines. 57,58 However, no comprehensive studies of the role of specific volatiles have been reported.…”