The color preference of bumblebee nectar robbing and its impact on the reproductive fitness of Lonicera calcarata

doi:10.17520/biods.2024554

Abstract

Abstract:

Aims:The color change of flowers during their blooming process can serve as a cue that guides pollinators to preferentially visit pre-change color flowers. However, it remains unclear whether this color change influences nectar robbers’ behavior.

Methods:To explore whether nectar robbers prefer pre-change color flowers and the impact of nectar robbing on plant reproductive success, we used Lonicera calcarata (Caprifoliaceae) as the study subject. Its flowering period lasts for three days, during which the flower color changes from white to yellow and then to orange-red. We recorded the visitation behavior of flower-visiting insects in the field and calculated the frequencies of legitimate visits and nectar robbing. We also analyzed the nectar robbing rates of flowers of three colors in different populations, measured the morphological traits of normal and robbed flowers, assessed the nectar volume and sugar concentration in both normal and robbed flowers during blooming, and examined the total number of pollen grains and ovules in flower buds from normal and robbed flowers. Finally, we performed different artificial pollination treatments to calculate seed set.

Results:Flower visitors to L. calcarata included moths, butterflies, and bumblebees, among which bumblebees could both legitimately visit the flowers and rob nectar from flowers of different colors. The overall nectar robbing frequency was higher than the frequency of legitimate visits for bumblebees. Nectar robbing rates of L. calcarata varied across different populations, with the nectar robbing rate of orange-red and yellow flowers being significantly higher than that of white flowers. The floral traits of robbed flowers were smaller than normal flowers in general, especially the lip and anther size. The holes in nectar spurs of orange-red and yellow flowers were significantly larger than those in white flowers. In all the three phases, nectar robbing significantly reduced the nectar volume of one flower, but did not affect the nectar sugar concentration. There were no significant differences in the total number of pollen grains in the buds between robbed and normal flower, as well as the ovules. Seed sets of pollen grains from normal and robbed flowers pollinated on the stigmas of normal flowers were not significantly different. Likewise, the seed sets of pollen from normal flowers pollinated on the stigma of normal and robbed flowers showed no significant differences.

Conclusion:This study preliminarily indicates that nectar robbing bees, particularly bumblebees, do not preferentially visit pre-change color flowers. Nectar robbing reduces nectar secretion and it does not directly affect the plant’s female and male fitness. The influence of flower color change on flower-visiting insect behavior requires further and more sustained investigation.

Key words: nectar robbing, reproductive fitness, pollinator, nectar robber, Lonicera calcarata, floral color change

Wang Shunyu, Li Yang, L‌ü Xiaoqin, Li Xin, Fan Quanxiu, Wang Xiaoyue. The color preference of bumblebee nectar robbing and its impact on the reproductive fitness of Lonicera calcarata[J]. Biodiv Sci, 2025, 33(4): 24554.

Add to citation manager EndNote|Ris|BibTeX

URL: https://www.biodiversity-science.net/EN/10.17520/biods.2024554

https://www.biodiversity-science.net/EN/Y2025/V33/I4/24554

Figures/Tables 6

Fig. 1 Inflorescence and single flower of Lonicera calcarata and the visiting behavior of insects. A. White, yellow and orange-red flowers on the branch of L. calcarata; B. Nectar robbing phenomenon (using the white flower as an example, the hole marked with a red arrow); C. Diagram showing the measurement of floral traits (a, Upper lip length; b, Upper lip width; c, Lower lip length; d, Lower lip width; e, Floral opening diameter; f, Floral tube diamete; g, Floral tube depth; h, Nectar spur length; i, Nectar spur diameter; j, Pistil length; k, Stigma diameter; l, Stigma thickness; m, Stamen length; n, Anther length; o, Anther width; p, Anther thickness; q, Robbing hole’ length; r, Robbing hole’s width); D. Bombus melanurus forages the nectar through the corolla opening (legitimate visit); E. B. melanurus inserts its proboscis into the nectar spur’s base to rob nectar; F. B. eximius visits the flowers legitimately; G. B. eximius robs the nectar from the base of the nectar spur; H. B. sonani visits the flowers legitimately; I. B. sonani robs the nectar from the base of the nectar spur; J. Aporia agathon visits the flowers legitimately; K. Moths visits the flowers legitimately.

Table 1 The locations of the seven wild populations of Lonicera calcarata and comparison of nectar robbing rates of white, yellow, and orange-red flowers in each population (generalized linear model analysis). Different lower case letters in the same row indicate significant differences in nectar robbing rate among the different color flowers.

居群 Population	位置 Location			盗蜜率 Nectar robbing rate (%)			Wald χ²	df	P
	纬度 Latitude (°N)	经度 Longitude (°E)	海拔 Altitude (m)	白色花 White flowers	黄色花 Yellow flowers	橘红色花 Orange-red flowers	Wald χ²	df	P
1	23.14	104.81	1,939	15.81 ± 5.30^b	58.53 ± 13.36^a	60.88 ± 14.68^a	12.107	2	0.002
2	23.24	104.91	1,953	41.67 ± 22.05^b	89.71 ± 7.55^a	96.97 ± 3.03^a	12.895	2	0.002
3	23.16	104.82	1,920	32.82 ± 3.41^b	80.16 ± 8.40^a	83.33 ± 9.62^a	26.701	2	< 0.001
4	23.19	104.86	1,930	16.90 ± 6.91^b	34.17 ± 19.73^a	75.35 ± 9.01^a	22.566	2	< 0.001
5	23.29	104.76	1,941	11.97 ± 4.93^b	65.19 ± 17.12^a	72.50 ± 7.25^a	56.944	2	< 0.001
6	22.69	105.76	1,817	35.42 ± 7.38^b	32.97 ± 7.67^ab	58.78 ± 8.58^a	8.746	2	0.013
7	22.19	105.16	1,761	0.00 ± 0.00^c	20.00 ± 16.33^b	38.89 ± 18.59^a	42.372	2	< 0.001

Fig. 2 Comparison of the frequency of legitimate visits (completing the pollination process) and nectar robbing behavior of Aporia agathon, moths, Bombus melanurus, B. eximius and B. sonani on Lonicera calcarata. Different uppercase letters indicate significant difference in the frequency of legitimate visits among different insects, while different lowercase letters indicate significant difference in the frequency of nectar robbing behavior among different insects. “ns” indicates no significant difference between the frequency of legitimate visit and nectar robbing behavior of the same insect (P > 0.05), while *** indicates that the nectar robbing frequency is significantly higher than the frequency of legitimate visits of the same insect (P < 0.001).

Table 2 Comparison of floral characters between robbed and normal unrobbed flowers (white, yellow and orange-red) of Lonicera calcarata and nectar robbing hole size among these three colors flowers (mean土SE, units: mm, generalized linear model analysis). Different lowercase letters in the same row for one color flower indicate significant difference in the floral characters between robbed and normal flowers, with larger value in bold.

Fig. 3 Comparison of nectar volume (A) and sugar concentration (B) during three flowering stages of normal and robbed Lonicera calcarata flowers. Different uppercase letters indicate significant difference in nectar volume or sugar concentration of normal L. calcarata flowers at different stages. Different lowercase letters indicate significant difference in nectar volume or sugar concentration of robbed L. calcarata at different stages. *** indicates a significant difference (P < 0.001) between two treatments at the same stage, and “ns” indicates no significant difference (P > 0.05) between two treatments at the same stage.

Fig. 4 Comparison of total number of pollen grains (A) and ovules (B) between normal and robbed flower buds of Lonicera calcarata, and comparison of seed sets among different pollination treatments (C). Normal pollen * robbed stigma, abbreviated to NP*RS; normal pollen*normal stigma, abbreviated to NP*NS; robbed pollen * normal stigma, abbreviated to RP*NS. “ns” indicates no significant difference between the different treatments (P > 0.05).

References 36

[1]	Carrió E, Güemes J (2019) Nectar robbing does not affect female reproductive success of an endangered Antirrhinum species, Plantaginaceae. Plant Ecology & Diversity, 12, 159-168.
[2]	de Souza CV, Salvador MV, Tunes P, Di Stasi LC, Guimarães E (2019) I’ve been robbed! Can changes in floral traits discourage bee pollination? PLoS ONE, 14, e0225252.
[3]	Deng H, Xiang GJ, Guo YH, Yang CF (2017) Study on the breeding system and floral color change of four Lonicera species in the Qinling Mountains. Plant Science Journal, 35, 1-12. (in Chinese with English abstract)
	[邓惠, 向甘驹, 郭友好, 杨春锋 (2017) 秦岭忍冬属4种植物的繁育系统及花色变化的研究. 植物科学学报, 35, 1-12.]
[4]	Eidesen PB, Little L, Müller E, Dickinson KJM, Lord JM (2017) Plant-pollinator interactions affect colonization efficiency: Abundance of blue-purple flowers is correlated with species richness of bumblebees in the Arctic. Biological Journal of the Linnean Society, 121, 150-162.
[5]	Feng HH, Wang XY, Luo YB, Huang SQ (2023) Floral scent emission is the highest at the second night of anthesis in Lonicera japonica(Caprifoliaceae). Journal of Systematics and Evolution, 61, 530-537.
[6]	Hazlehurst JA, Karubian JO (2016) Nectar robbing impacts pollinator behavior but not plant reproduction. Oikos, 125, 1668-1676.
[7]	Heiling JM, Ledbetter TA, Richman SK, Ellison HK, Bronstein JL, Irwin RE (2018) Why are some plant-nectar robber interactions commensalisms? Oikos, 127, 1679-1689.
[8]	Hou QZ, Ehmet N, Chen DW, Wang TH, Xu YF, Ma J, Sun K (2021) Corolla abscission triggered by nectar robbers positively affects reproduction by enhancing self-pollination in Symphytum officinale(Boraginaceae). Biology, 10, 903.
[9]	Inouye DW (1983) The ecology of nectar robbing. In: The Biology of Nectaries (eds Bentley B, Elias T), pp. 153-173. Columbia University Press, New York.
[10]	Irwin RE, Brody AK (1999) Nectar-robbing bumble bees reduce the fitness of Ipomopsis aggregata(Polemoniaceae). Ecology, 80, 1703-1712.
[11]	Irwin RE, Bronstein JL, Manson JS, Richardson L (2010) Nectar robbing: Ecological and evolutionary perspectives. Annual Review of Ecology, Evolution, and Systematics, 41, 271-292.
[12]	Irwin RE, Howell P, Galen C (2015) Quantifying direct vs. indirect effects of nectar robbers on male and female components of plant fitness. Journal of Ecology, 103, 1487-1497.
[13]	Irwin RE, Maloof JE (2002) Variation in nectar robbing over time, space, and species. Oecologia, 133, 525-533. DOI PMID
[14]	Li JJ, Lian XY, Ye CL, Wang L (2019) Analysis of flower color variations at different developmental stages in two honeysuckle (Lonicera japonica Thunb.)cultivars. HortScience, 54, 779-782.
[15]	Mackin CR, Goulson D, Castellanos MC (2021) Novel nectar robbing negatively affects reproduction in Digitalis purpurea. Ecology and Evolution, 11, 13455-13463.
[16]	Maidana-Tuco YN, Larrea-Alcázar DM, Pacheco LF (2024) Nectar robbing effects on pollinators of a key nectar source plant (Tecoma fulva, Bignoniaceae) in a dry tropical Andean valley. Biotropica, 56, e13319.
[17]	Makino TT, Ohashi K (2017) Honest signals to maintain a long-lasting relationship: Floral colour change prevents plant-level avoidance by experienced pollinators. Functional Ecology, 31, 831-837.
[18]	Maloof JE (2001) The effects of a bumble bee nectar robber on plant reproductive success and pollinator behavior. American Journal of Botany, 88, 1960-1965. PMID
[19]	Ohashi K, Makino TT, Arikawa K (2015) Floral colour change in the eyes of pollinators: Testing possible constraints and correlated evolution. Functional Ecology, 29, 1144-1155.
[20]	Raine NE, Chittka L (2007) Flower constancy and memory dynamics in bumblebees (Hymenoptera: Apidae: Bombus). Entomologia Generalis, 29, 179-199.
[21]	Richman SK, Barker JL, Baek M, Papaj DR, Irwin RE, Bronstein JL (2021) The sensory and cognitive ecology of nectar robbing. Frontiers in Ecology and Evolution, 9, 698137.
[22]	Rojas-Nossa SV, Sánchez JM, Navarro L (2016) Effects of nectar robbing on male and female reproductive success of a pollinator-dependent plant. Annals of Botany, 117, 291-297. DOI PMID
[23]	Rojas-Nossa SV, Sánchez JM, Navarro L (2021) Nectar robbing and plant reproduction: An interplay of positive and negative effects. Oikos, 130, 601-608. DOI
[24]	Sun SG, Liao K, Xia J, Guo YH (2005) Floral colour change in Pedicularis monbeigiana(Orobanchaceae). Plant Systematics and Evolution, 255, 77-85.
[25]	Tie S, He YD, Lázaro A, Inouye DW, Guo YH, Yang CF (2023) Floral trait variation across individual plants within a population enhances defense capability to nectar robbing. Plant Diversity, 45, 315-325. DOI
[26]	Traveset A, Willson MF, Sabag C (1998) Effect of nectar-robbing birds on fruit set of Fuchsia magellanica in Tierra Del Fuego: A disrupted mutualism. Functional Ecology, 12, 459-464.
[27]	Varma S, Rajesh TP, Manoj K, Asha G, Jobiraj T, Sinu PA (2020) Nectar robbers deter legitimate pollinators by mutilating flowers. Oikos, 129, 868-878.
[28]	Wang XY, Yao RX, Lv XQ, Yi Y, Tang XX (2023) Nectar robbing by bees affects the reproductive fitness of the distylous plant Tirpitzia sinensis(Linaceae). Ecology and Evolution, 13, e10714.
[29]	Weiss MR (1991) Floral colour changes as cues for pollinators. Nature, 354, 227-229.
[30]	Weiss MR, Lamont BB (1997) Floral color change and insect pollination: A dynamic relationship. Israel Journal of Plant Sciences, 45, 185-199.
[31]	Willmer P (2011) Pollination and Floral Ecology. Princeton University Press, Princeton.
[32]	Yang QE, Sven L, Joanna O, Renata B (2011) Lonicera. In: Flora of China, Vol. 19 (eds Wu ZY, Raven PH, Hong DY), pp. 620-641. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis.
[33]	Ye ZM, Jin XF, Wang QF, Yang CF, Inouye DW (2017) Nectar replenishment maintains the neutral effects of nectar robbing on female reproductive success of Salvia przewalskii (Lamiaceae), a plant pollinated and robbed by bumble bees. Annals of Botany, 119, 1053-1059.
[34]	Zhang YW, Wang Y, Guo YH (2006) The effects of nectar robbing on plant reproduction and evolution. Journal of Plant Ecology (Chinese Version), 30, 695-702. (in Chinese with English abstract)
	[张彦文, 王勇, 郭友好 (2006) 盗蜜行为在植物繁殖生态学中的意义. 植物生态学报, 30, 695-702.] DOI
[35]	Zhu XF, Wan JP, Li QJ (2010) Nectar robbers pollinate flowers with sexual organs hidden within corollas in distylous Primula secundiflora (Primulaceae). Biology Letters, 6, 785-787.
[36]	Zimmerman M, Cook S (1985) Pollinator foraging, experimental nectar-robbing and plant fitness in Impatiens capensis. American Midland Naturalist, 113, 84.