Do Bees Pollinate Tomatoes?

Updated: 1st may 2021


Question:
Do bees pollinate tomatoes?

The short answer is ‘yes’, but...
Bumble bees can pollinate tomatoes, but in a domestic greenhouse, bumble bees are not required for pollination. There is no need to encourage bees into the greenhouse to pollinate tomatoes.


According to Prof Dave Goulson in ‘Bumblebee Behaviour And Ecology’, tomatoes are self-fertile, and capable of self pollination, but insect visits are needed to move pollen from the anthers to the stigma of the flower.

However, this raises questions for the gardener who chooses to grow their tomatoes in a greenhouse (this includes me, by the way!) – and I’ll get onto this point in a moment.


How Do Bees Pollinate Tomatoes?

Bumble bee pollinating tomato flower.Bumble bee pollinating tomato flower.

The anthers of tomato flowers only release pollen when vibrated.  Bumble bees are able to achieve this through ‘buzz pollination’.  This means the bumble bee places its upper body (thorax) close to the anthers, and vibrates its flight muscles at a frequency of about 400Hz (King 1993).  This literally shakes the pollen from the anther.

red cherry tomatoes we harvested from one of our tomato plants, in a white dish on the garden table.Some of the cherry tomatoes we harvested from one of our tomato plants.

Prior to the understanding that bumble bees pollinate tomatoes so efficiently, people were employed in glasshouses to pollinate tomatoes using a vibrating tool.  Obviously this was labour intensive and costly.  However, it has been found that bumble bees enable a greater yield of tomatoes than hand pollination (Banda and Paxton 1991).


How Do We Know If Bumble Bees Have Pollinated The Tomatoes?

It’s fascinating that commercial suppliers of bumble bees, have discerned how growers can check on the level of pollination of tomatoes by bumble bees. 

Bumble bees bite onto the flower each time they visit, leaving tiny, but visible bite marks.  One set of bite marks is enough to indicate that pollination will have occurred.  However, the more sets of bite marks on your flowers, the more bumble bee visits, and this means more tomato fruits. 


However, it is also worth noting that there is more to it than simply increasing the number of visits by bumble bees in a glass house.  If you are a commercial grower, it requires careful monitoring of issues such as temperature and humidity. 

For example, too little humidity means the germination capacity of the pollen decreases, so that even if bumble bees collect the pollen, no fruit will grow.   If humidity is too high, it means that the flower will not release pollen for bees to collect.  I am not clear on whether this would put bees at risk if they are unable to feed and are trapped in a greenhouse.  Presumably, it may cause a little difficulty until they have access to food again.

Anyway, all this is certainly beyond my needs as a gardener and home producer of tomatoes which I have been doing for some years now, but I’ll come on to this in a moment.


Do Other Bee Species Pollinate Tomatoes?

I believe Xylocopa - large carpenter bee species are also very good pollinators of tomato flowers. 

I am not clear about the role of other solitary bees in the pollination of tomato plants, however, honey bees, despite being valuable pollinators of many crops, do not buzz pollinate.  

Also, research suggests that they will not visit tomato plants from preference, and crop yield is erratic (Spangler and Moffet 1977, Banda and Paxton 1991 – as cited in Goulson’s Bumblebee Behaviour And Ecology).


What About Bees For My Greenhouse?

I grow tomatoes for outdoors and inside a greenhouse.  Obviously, outdoor tomato plants can easily be pollinated by bumble bees.   If you have the space, perhaps you could grow a couple of plants (mine are cherry tomatoes growing in containers, but there are other varieties).

large spider with its parceled up prey in cobweb in the greenhouse.A bee parceled up in a spider web in our greenhouse - I no longer leave the door open! I still end up with a glut of tomatoes every year!

UPDATE:  I used to leave the greenhouse door open for bumble bees, but found that they, solitary bee species and butterflies too easily became trapped.   For some years now, I have used netting in front of the door when it is open, to prevent bees getting in and being trapped in spider webs.

I have been growing tomatoes in my 6ft x 8ft greenhouse for almost 10 years.  I find we grow sufficient tomatoes without the need for bumble bee pollination, such that we are able to freeze any glut and continue using the tomatoes (casseroles, pasta sauces) well into spring the following year.   


If Bumble Bees Pollinate Tomatoes, Wouldn’t It Be Easier If I Just Buy A Box Of Bees For The Greenhouse?

In some countries, it is possible for gardeners to purchase boxes of bumble bees, including native species.  However, I do not recommend it. 

Despite being native species, there is a risk of transmission of diseases to wild bees.  In addition to which, commercial growers run a very carefully monitored and specialised business, and using bees to pollinate is not necessarily simple. 

In other words, you have to know what you are doing. 

For example according to Koppert, a supplier of bumble bees, over-pollination can occur, where starving bumble bees find they do not have enough food in the greenhouse, and so they shake the flower so much, that this can result in malformed fruit.  

With regard to nectar, according to Koppert, tomatoes do not produce any, and bees need it.  In commercial operations, growers have to take into account all these factors. 

Now good luck with your tomatoes!


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