31 January, 2024

Insect pollinators are critical not only for producing crops to feed humans, but also for producing food to feed wildlife

A female ivy bee (Colletes hederae) feeding
on ivy flower (Photo by Steven Falk).

by M. Lam, I. Ryan, L.V. Dicks

Climate change and human activities are causing insect pollinator declines in many parts of the world. This has direct consequences for human food production, since many crop species require insect pollination to produce seeds_ and fruits (termed “pollinator dependence”). Pollination can also improve the quality of crop harvests, such as larger and/or more nutritious fruits. However, declining pollinator populations can negatively impact food chains in nature too. Many wild flowering plants also rely on insect pollination to produce fruits, which feed other animals. In the UK, ivy fruits feed some of our best-loved birds, including song thrushes and winter visitors like the fieldfare. Previous research suggests that ivy shows pollinator dependence – if this is true, then pollinator declines can reduce the food supply for many fruit-eating animals. However, the extent of such dependence and whether pollination affects the quality of fruit remains unknown. 

To address this missing knowledge, we investigated the importance of pollination to ivy fruit production in terms of quantity and quality, as well as how that can affect the feeding choices of animals. We conducted this study in a mixed woodland-meadows nature reserve and a botanical garden in Cambridge. We manipulated the level of pollination received by ivy plants and found that the quantity and quality of fruit depends strongly on insect pollination. Without the help of insect pollinators, the production of fruits in ivy dropped dramatically by 90%, and the fruits were also smaller. Monitoring the survival of ivy fruits revealed that animals can prefer well-pollinated fruits. At the woodland site, over 99% of fruits which received extra pollen were eaten, whereas over half of the unpollinated fruits remained untouched. Hence, the initial level of pollination also influences animal feeding choices.

This study highlights how pollinator declines can have far-reaching effects in ecosystems by reducing the fruit supply for animals. It is therefore necessary for us to maintain the health of pollinator communities, so that food supply for animals and the stability of food chains are protected in nature.

19 January, 2024

The tripping mechanism of flowers affects pollen transfer dynamics

by Dieterich Mabin et al.

Bumble bee on alfalfa with some tripped flowers  

Insect pollinators move pollen between flowers and plants, and therefore affect pollen transfer, pollen movement, and pollen dispersal. Two important components of pollen transfer dynamics include the accumulation of pollen on a bee’s body as a bee visits flowers in succession, and the number of pollen grains deposited on the stigma as a bee revisits a flower. These characteristics have typically been described in plants without a tripping mechanism. However, the flowers of many plant species in the families Labiatae and Fabaceae have closed flowers that require a pollinator or other force to exert pressure on the keel of a flower in order to release the anthers and stigmas. In this study, we investigate the two fundamental aspects of pollen transfer dynamics mentioned above for a bumble bee species visiting flowers with a tripping mechanism. The number of pollen grains on a bee’s body increased with the number of flowers tripped by a bee. In fact, for each flower tripped in a foraging bout, the number of pollen grains on a bee’s body increased by an average of 954 grains. However, revisiting tripped flowers did not increase the number of pollen grains deposited on a stigma. This contrasts with flowers that do not have a tripping mechanism where the number of pollen grains deposited on a stigma increases with the number of pollinator visits to a flower. Moreover, plants with a tripping mechanism can be categorized into two groups, one where the flowers remain open after tripping such as the plant species used in this study, Medicago sativa, commonly known as alfalfa or lucerne, and the other where the flowers close after tripping as occurs in clover or Trifolium species. We hypothesize that staggered anther dehiscence, where pollen is released over time from a flower, would be beneficial in plant species whose flowers close after tripping. Moreover, revisits to a flower could increase pollen deposition on stigmas in flowers that close after tripping especially if staggered anther dehiscence is present. Tripping of a flower affects pollen transfer dynamics, and the effect may vary with the mode of tripping.

Read the scientific publication in JPE here.