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

Ann Gaffney,Björn Bohman,Stephen R Quarrell,Geoff R Allen,Philip H Brown

doi:10.3390/insects11070402

Abstract

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.

Highlights

Carrot flowers are unattractive to honey bees (Apis mellifera Linnaeus), which often seek out other available forage [1]
97.8% were from four groups; 53.8% were from nectar scarabs, 25.1% were from honey bees, 15.5%
Total insect visitation was found to be significantly different among root types (Kruskal–Wallis test χ2 = 42.31, df = 7, p < 0.001) with Berlicumer root cultivars being visited by significantly more insects (7.8 ± 0.8 visits per 5 min) than Nantes (5.4 ± 0.5 visits per 5 min) (Mann–Whitney test U = 3109, p = 0.0011)

Summary

Introduction

Carrot flowers are unattractive to honey bees (Apis mellifera Linnaeus), which often seek out other available forage [1]. There are many visual and olfactory floral traits, including morphology, colour, nectar composition, and floral volatiles, which separately or collectively make one flower distinguishable from another to a pollinator [16,17,18]. Some pollinators such as honey bees are opportunistic foragers, whose tendencies for innate responses can be altered by learning, mainly via olfactory conditioning [19,20].

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Discussion

Conclusion