Two Prolonged Bee Visits Suffice to Maximize Drupelet Set for Red Raspberry by Corey J. Andrikopoulos and James H. Cane, Utah State University, Logan, HORTSCIENCE 53(10):1404–1406. 2018. https://doi.org/10.21273/HORTSCI13124-18
Everyone knows that insect pollination is critical for fruit set in many commercial berry species. The red raspberry is no exception. It produces an aggregate fruit composed of individual drupelet fruits. If the weather is bad, the insects are not flying, or something else interrupts pollination, you can easily get misshapen fruit and lower yields. Researchers at Utah State found that it only takes two prolonged visits of 1 minute or more to get great fruit set. You don’t need hundreds of bees visiting the flowers. Here are a few tidbits about red raspberries from this article:
- Red raspberries are mostly self fertile but because the pollen bearing anthers are not located directly adjacent to the female stigmas, self pollination can be spotty.
- A single flower bears 60 – 90 stamens with ample pollen, but bees and other insects are needed to move the pollen to the central region of female stigmas. Each individual stigma needs to be pollinated to get a good fruit.
- Previously scientists estimated that up to 68 visits per flower were necessary to get adequate fruit set, but these authors showed that 2 visits were great.
- For two visits to be adequate, the bee must really work the flower for a prolonged period of time (up to a minute or more). Bees often spend long times on a newly opened flower first thing in the morning because that’s when nectar flow is at its peak after a night time of storing up nectar in the flower’s nectar pool.
- Individual flowers remain receptive for about 2 days, and every morning the nectar pool is recharged. Nectar release is temperature dependent.
- By individually covering flowers as they bloomed and comparing them to uncovered controls, the researchers showed that bee visits increased drupelet formation by 2 to 4 times. If a flower was visited first thing in the day for a prolonged period, two such visits would be sufficient to have great fruit formation.
- There is also a condition of over visitation where bees actually damage the female stigmas if there are too many of them working the flowers.
Adding honey bee hives to a raspberry garden is a good idea for most commercial businesses. However, Alaska temperatures, especially in the a.m. can be cold – too cold for honey bees to be very active. Since nectar flow is greatest first thing in the morning, wild bumble bees become even more critical for great fruit set in northern gardens.
This is a summary of Rehanon Pampel’s thesis documenting bumble bees in agricultural areas of the Interior. It documents species as well as seasonal occurrence. You think bumbles are doing their thing all summer, but there is a definite seasonal pattern to their work.
Here is a link to a journal article comparing native and non-native pollinators of Haskap. They concluded that native bumble bees (compared to orchard bees and honey bees) have the highest pollen deposition per visit, visited the most flowers in a given period of time and could fly at the coldest temperatures, making them the most suited for successful pollination at least in cooler springs. Another interesting thing to note is Figure 1c in the paper. It shows a fruit in which the bracteoles have not fused around the two ovaries of the paired flowers. I find this interesting because I observed several fruits shaped like this and wondered what caused it. Understanding the biology of the flower, the formation makes more sense! KD Fairbanks
Frier, S.D, C.M. Somers and C.S. Sheffield. 2016. Comparing the performance of native and managed pollinators of Haskap (Lonicera caerulea: Caprifoliaceae), an emerging fruit crop. Agriculture, Ecosystems and Environment 219:42-48.
It was all over the internet recently, bumble bees were put on the endangered species list. Research into this decision told me that the “rust-patched” bumblebee (Bombus affinis) was the pollinator. According to the U.S. Fish and Wildlife Service, the bee can be found in the eastern portion of the United States and in some parts of Canada. The Alaskan Department of Fish and Game cites Bombus polaris, the Arctic bumblebee, in this article describing the life of a bumble bee in Alaska. Because they are important pollinators, this is of horticultural interest. The article can be found here:
Sutton, A. n.d. A brief busy life of the arctic bumblebee. Available online: Bumble bees
U.S> Fish and Wildlife Service. 2016. Rusty Patched Bumble Bee. Available online: Rusty patched
. Accessed 5 Oct, 2016
The Leonard Lab at The University of Nevada Reno has been conducting some neat experiments on pollination. Here is a link to a write up of one study showing bumble bee recognition of flower color in association with pollen rewards. They are such smart creatures! Bumble bee learning
If you’re a gardener, berry lover, or if you eat food, it wouldn’t hurt to spend a little more time appreciating our pollinators. One of my favorite authors, Rowan Jacobsen, wrote an enlightening book on the topic of pollination–Fruitless Fall (see below), in particular, on colony collapse disorder in honeybees. It’s frightening to think about the fragility of our current system of pollination. Luckily, wild berries in Alaska do not depend on managed hives for pollination. On my reading list since I read Fruitless Fall is Forgotten pollinators. We should probably all spend a little more time appreciating these flying wonders. I enjoyed watching the beautiful video of buzz pollination(see below) And while we’re on the topic, check out the Xerces society. They have a plethora of great resources on protecting and appreciating our sometimes forgotten and under-appreciated invertebrates. HR Fairbanks
Buchman, S. L. 1997. Forgotten pollinators. Island Press.
Jacobsen, R. 2010. Fruitless Fall: The Collapse of the Honey Bee and the Coming Agricultural Crisis. Bloomsbury, USA.
Xerces Society for Invertebrate Conservation (Home Page). 2016. Available at: http://www.xerces.org.
14 Sept, 2016.
Pollination is the process that leads to the production of the fruits we eat and the seeds we need to grow more plants. It is the process of transferring pollen from flowers to flowers to aide fertilization and encourages new propagation. Natural pollinators are highly effective and although man can mimic the pollination process done by many species, no amount of mimicry can compare to the efficiency of the many different bee species. Of the large variety of bee species, I find the bumble bee to be the easiest to identify as well as the easiest to actually see the pollination process.
There are over 250 bumble bee species worldwide with 49 of them being native to North American (Inouye). Scientifically they can be identified by dividing them into three groups based on the length of their proboscis or tongue (long, medium and short), but the best way to identify a bumble bee is by its fairly large round shape, super fuzzy body and the amplified buzzing sound emitted by their wings. The bumble bees tend to build nests in old hollowed out logs, abandoned rodent holes and other locations down on the ground. The queen will borrow into the ground and hibernate throughout the winter while the rest of the colony will die off in fall. During the spring the new queens come out of their borrow, find a suitable place for a nest and begin to collect pollen and nectar to help feed the first generation of worker bees to hatch. The bumble bee queens will rear a few generations of worker bees which are all non-fertile females to help collect pollen and nectar to help feed the final generation, next year’s queens and fertile males (NPS).
The bumble bee is a hugely important pollinator because of the efficient techniques in which these bees can collect and transfer pollen. The bumble bee will bite the flower in its jaws and use its flight muscles to microscopically and violently vibrate the pollen grains off the flowers anthers this is called buzz pollination or sonication (Inouye). The pollen will stick to the fuzzy body of the bumble bee as well as sticking to what is referred to as pollen baskets or sacs on the back legs. As the bumble bee flies from flower to flower each time carrying away a little pollen as well as transplanting pollen from flower to flower and possibly fertilizing hundreds. “The average mass of pollen and nectar carried by bumblebees returning to the nest is around 25% of their body weight. However some bumblebees fly back carrying as much as 75% or more of their body weight!” (Nature mapping).
Humans are deeply invested in the health status of bee populations because of the environmental services they provide and because of it many species are being commercially developed and shipped all over the globe, even in places they don’t naturally occur. Another hot topic is that bees are of conservation concerns. Human activities including habitat degradation, pesticides, diseases and floral resource depletion can have detrimental effects to bee populations (Inouye). Bees are of major importance to the Earth’s ecosystem functionality and are worth giving a second thought before smashing them out of fear of being stung. Next time you got a big bumble headed your way, think about the significant job that bee performs before reacting with fear. LH Fairbanks
“Bumblebee.” Nature Mapping Foundation. N.p., n.d. Web. 22 Sept. 2016.
Inouye, David. “Bumblebees (Bombus Spp.).” United States Department of Agriculture Forest Service. University of Maryland, n.d. Web. 22 Sept. 2016.
“Pollinators – Bumble Bee.” National Park Services. U.S. Department of the Interior, n.d. Web. 21 Sept. 2016.