植物开花过程中花色的变化作为一种指示信号会引导传粉者偏好访问变色前的花, 那么花色的变化能否影响昆虫盗蜜, 目前还不清楚。为了探究盗蜜者是否偏好变色前的花以及盗蜜对植物繁殖适合度的作用, 我们以忍冬属长距忍冬(Lonicera calcarata)为研究对象, 其花期3天, 花色从白变为黄, 再变为橘红, 野外记录访花昆虫的访问行为, 计算合法访问和盗蜜的频率; 统计不同居群3种颜色花的盗蜜率, 测量它们正常和盗蜜花朵的形态特征, 测量开花中正常和盗蜜花朵的花蜜现存量和糖浓度, 统计正常和盗蜜的花苞中花粉和胚珠总数, 进行不同人工授粉处理统计结实率。长距忍冬的访花者有尺蛾、蝶和熊蜂, 其中熊蜂可以合法地访花和对不同颜色的花盗蜜, 总的盗蜜频率高于合法访花频率; 橘红色和黄色花的盗蜜率、盗洞大小显著高于白色花; 盗蜜花的形态特征(尤其是唇瓣和花药)整体上小于正常花, 盗蜜减少单花的花蜜分泌量, 但不影响其糖浓度; 盗蜜不影响花苞中的花粉总数、胚珠数和植株的结实率。该研究表明盗蜜者熊蜂没有偏好访问变色前的花, 盗蜜会减少花蜜分泌量, 没有直接显著影响植物的雌雄适合度。植物花色变化对访花昆虫行为的影响需要更深入和持续的研究。

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.