infrequently asked questions

Bees pollinate one-third of what? Do we really know?

Dear Readers,

Almost every day I read something like this: “One third of all the food we eat is pollinated by bees.” I just read it again today–twice. Some say “every third bite” which sounds like volume; some say “one-third of all crops” which sounds like a species count.

Please tell me about this one third. Is it one-third by weight, volume, calories, dollars, species, or some other measurement I haven’t thought of? I would like to know who came up with this number and how it was calculated. I would also like to know if they really mean bees, or if they mean pollinating insects, or all pollinating animals.

The thing is, it’s hard to defend an argument when you have no clue how the numbers were obtained. I’ve had several readers ask me where the one-third came from and it’s embarrassing not to know. It feels like that circle game where you keep passing on a message, and by the time the last person gets it, it’s totally garbled and nothing like the original.

If anyone can help, I would greatly appreciate hearing from you. There are many other people waiting to hear the answer as well. Remember, we will never be persuasive in our bid to save pollinators, if we are not believable in our statistics. Please help me figure this out!


One-third of what?


  • I’m going to look this up when I get home. I agree with you. My first instinct is to turn to the Xerces Society. this article has a bunch of numbers in it, but i didn’t do the math to see if any of them come out to 1/3, and i dont think there are any sources cited!

    • Allow me to save you the trouble jess, and also allow me, to help you to get it right. In North America insects and all other animal pollinators only account for 5% of the food we eat. In the third world that number is about 8%. All the insect, bat, and hummingbird pollinated crops in total account for less than 6-7% of all food produced on Earth, and the honey bee is responsible for only a fraction of that. The thing that make’s the honey bee valuable to agriculture is its ability to quickly pollinate large numbers of flowers over a wide area making it possible to grow mono-cultural crops like canola, or almonds.

      When you grow large fields or orchards of mono-cultured crops, natural pollinators can only pollinate a small percentage of the flowers in the short period of time that nature allots for this work. Usually less than 24 hours per flower, and many times much much less than 24 hours. These insect pollinated crops are also mostly what we humans consider high value or luxury food items, like peaches, coffee, almonds, or vanilla. Some crops like cotton or soybeans can even harm the farmers bottom line if they receive too much, or the wrong type of insect pollination, and I suspect that there are other crops like these..

      I have keep bees off and on for over 50 years and I have never heard of the “American Beekeepers Federation.” It sounds like a tax dodge or way to avoid paying your fair share to me.

      It would have been better if you had read what Dr. Keith Delaplane actually said before you posted. Above is one link to the good doctor’s valuable work.

      Remember, a honey bee making honey from nectar or even gathering pollen from crops is not the same thing as pollination. As much as 60% of the pollen gathered by bees is corn pollen and corn is both wind pollinated and also successfully grown in abandoned mine shafts by bio-tech companies to keep rare strains of maize pure for valuable traits or to keep GMO genes from escaping before they are tested and approved.

  • I didn’t forget about this, it just took me longer than I expected. Almost everything I can find refers back to the USDA Bee Research Lab, which actually doesn’t cite any sources when they make the “one third” claim on their website, and the other “source” I found was the American Beekeepers Federation, which as far as I know does not conduct actual scientific research, so I can only assume they stole it from the USDA. OK so this actually cites some sources:

    Domestic honeybees pollinate approximately $10 billion worth of crops in the U.S. each year (Watanabe, 1994)

    The Myrna Watanabe article was published in Science. I do not have an AAAS or Science membership/subscription so I cannot read it. Not sure if it even addresses the issue, since I have no idea what the value of all crops in the U.S. was in 1994 (was it $30 Billion?), how it was measured, and how well this data holds up in 2010.

    Animal pollinators are needed for the reproduction of 90% of flowering plants and one third of human food crops (Buchmann and Nabhan, 1996; Free, 1970 In Tepedino, 1979; and McGregor, 1976 In Tepedino, 1993).

    Buchmann and Nabhan, 1996 – The Forgotten Pollinators — if memory serves, this book is not pro-honey bee to say the least, so i can’t see it making that claim.

    Free, J. B. 1993. Insect Pollination of Crops. — this is like 600 pages long with 85 pages of references and I can ‘t find the complete text so, I’m not sure about it.

    Tepedino, V.J. 1979. — I assume this refers to The importance of bees and other insect pollinators in maintaining floral species composition. Great Basin Naturalist Memoirs 3: p. 139 – 150 (now called Western North American Naturalist). There is nothing remotely similar, so…? Conveniently enough, the Western North American Naturalist has their archives online ( here ) But there is a twist! There is nothing from Tepedino in 1979 #3. There is also no article by that name published by that journal ever, but Tepedino did write “Spatiotemporal variation in phenology and abundance of floral resources on shortgrass prairie” in Vol. 40 No. 3 in 1980 (so I assume this is the same article — Now, I am now forced into my second assumption about this one resource!?! Scandalous). My conclusion, upon reading this article (finally)? Tependino doesn’t research human food crops.

    McGregor, 1976 — I think this is our winner. Check this out : Author writes:

    McGregor’s 1976 estimate that one-third of the human diet can be traced directly or indirectly to animal pollination (see Table 4-1)

    This article also cites McGregor 1976 as the origin of the “third mouthful” concept. ( – Food security not (yet) threatened by declining pollination
    Jaboury Ghazoul & Lian Pin Koh — this is published other places but this is the easiest to download for free without subscription) Authors write:

    pollination, which is often portrayed as being necessary for every third mouthful we eat (McGregor 1976; and widely repeated since).

    This is supposed to be the Insect Pollination Handbook (originally published by McGregor in 1976 via USDA) claims to be continuously updated):

    In Tepedino, 1993 – I did not bother to look this up because I feel like the McGregor 1976 is the source of everyone’s claims so, what’s the point.

    I quickly flipped through the most recent version of the Pollination Handbook, and I can’t find anything about one third of human food crops or the third mouthful. I am not sure if it has been revised out and I should find a 1976 version to confirm, or if it is described differently in the original text. Maybe next time I have a little more brain power to spare, I will actually read it.

    I am willing to email or call the USDA about this!!! It has been bothering me since you posted this. I do feel pretty confident that I have traced it back to the original source, but I obviously can’t confirm how the number was arrived at and if it is good to use.

  • have you read Crop pollination by bees by Keith S. Delaplane and D. F. Mayer? On page 2 they discuss the one-third claim, states that it is probably accurate, and refers back to McGregor 1976 again. I really need to see if the library or someone has the original 1976 USDA publication, since it’s out of print and about $42 on amazon.

  • geez, sorry to leave 500 comments tonight. I keep posting and then reading more, then posting, then reading more. Yes, wild Saturday night. This is from the Pollination Handbook:

    Worldwide, more than 3,000 plant species have been used as food, only 300 of which are now widely grown, and only 12 of which furnish nearly 90 percent of the world’s food. These 12 include the grains: rice, wheat, maize (corn), sorghums, millets, rye, and barley, and potatoes, sweet potatoes, cassavas or
    maniocs, bananas, and coconuts (Thurston 1969).1 The grains are wind-pollinated or self-pollinated, coconuts are partially wind-pollinated and partially insect pollinated, and the others are propagated asexually or develop parthenocarpically. However, more than two-thirds of the world’s population is in Southeast Asia where the staple diet is rice. Superficially, it appears that insect-pollination has little effect on the world’s food supply – possibly no more than 1 percent.
    Within the United States, which accounts for only about 6 percent of the world’s population, about 286 million acres were cultivated in 1969. About 180 million acres were devoted to the wind pollinated or self- pollinated crops, primarily barley, corn, oats, rice, rye, sorghums and wheat, grass hay crops, sugar beets, sugar cane, potatoes, sweet potatoes, and tobacco. About 60 million acres were devoted to crops that may receive some benefit from insect pollination but are largely self-pollinating (beans, cotton, flax, peanuts, peas, and soybeans). About 40 million acres were devoted to hay crops produced from bee-pollinated seeds (alfalfa, clovers, lespedezas). About 6 million acres were devoted to producing fruits, vegetables, and nuts–most of which are dependent upon insect pollination. Table 1 lists the cultivated crop plants, discussed herein, that are dependent upon or benefited by insect pollination. These plants provide about 15 percent of our diet.
    The animal products we consume contribute about an equal amount to our diet. These include beef, pork, poultry, lamb, and dairy products–derived one way or another from insect-pollinated legumes such as alfalfa, clover, lespedeza, and trefoil.
    More than half of the world’s diet of fats and oils comes from oilseeds–coconuts, cotton, oil palm, olives, peanuts, rape, soybeans, and sunflower (Guidry 1964). Many of these plants are dependent upon or benefited by insect pollination. When these sources, the animal and plant products, are considered, it appears that perhaps one-third of our total diet is dependent, directly or indirectly, upon insect-pollinated plants.

  • What a prodigious amount of work! I am so impressed!

    I thought I had seen the “original research” in Crop Pollination by Bees (Delaplane & Mayer) but I hadn’t gotten around to getting it from the library again. But if it refers back to McGregor, I won’t bother.

    Somewhere in my piles of documents I have works by Tedpedino, Watanabe, Buchmann, and Free, but as far as I remember, each of these borrowed the number from someone else as well.

    Your last cite seems to have the most detail, but (as you point out) it still doesn’t answer the “percent of what” question.

    I can see you are getting just as frustrated as I am about this number. It’s easy to see how rumors spread. Since I published this post a number of people have sent me links to places where it has been used (and abused) even in otherwise believable works.

    Thank you so much for this. You have inspired me to resume digging and have saved me a lot of effort as well.

  • So, after a few hours of sleep, I can understand what “adds up” to one third, but I still can’t puzzle out if it is number of crops or calories or dollars or acres.

    15% of “our diet” (US diet) comes from “cultivated crop plants, discussed herein, that are dependent upon or benefited by insect pollination.” this refers to table 1, which is a list of cultivated crops.

    We get another 15% (“about an equal amount to our diet”) from “beef, pork, poultry, lamb, and dairy products–derived one way or another from insect-pollinated legumes such as alfalfa, clover, lespedeza, and trefoil.”

    the rest of the “one third” comes from “More than half of the world’s diet of fats and oils comes from oilseeds–coconuts, cotton, oil palm, olives, peanuts, rape, soybeans, and sunflower (Guidry 1964). Many of these plants are dependent upon or benefited by insect pollination.” — at this point he switches gears and goes to the “world’s diet,” while the other two numbers are based on US diets. (let’s not even wander down the road of people who don’t partake in animal proteins…)

    I really want to believe that if I could just read this correctly, I would understand where it comes from, but McGregor doesn’t cite anything but Guidry 1964, and that’s the smallest part of it.

  • Hi Jess and Rusty,
    thanks for going into this with so much verve!
    I was one of the readers asking about the source and the units of the ubiquitous “One Third” back in March. I am working on a bee-film-project and we have been getting quite frustrated in trying to confirm this number, so this information you dug up is really, really helpful! Even when it leaves some questions still unanswered…
    I agree with Rusty: “One third” is an important claim – it would be great if there were a way to assess its substance!

  • I did some more digging and came across this fairly recent Science-paper (Dixon, KW (2009) Pollination and restoration, Science, vol325 (5940) pp571-573) where I found these numbers:
    „In agriculture and horticulture, the economic value of pollination is well recognized, with 75% of crop species and 35% of crop value dependent on pollination by animals (1, 2)“

    I looked up the references (both available free online):
    1: Klein AM at al. (2007) Importance of pollinators in changing landscapes for world crops, Proc. R. Soc. B 274, 303–313, doi:10.1098/rspb.2006.3721
    2: C. Kremen, N. M. Williams, R. W. Thorp (2002) Crop pollination from native bees at risk from
    agricultural intensification, Proc. Natl. Acad. Sci. U.S.A. 99, 16812

    Klein et al. write: „In this review, we expand the previous estimates using novel primary data from 200 countries and found that fruit, vegetable or seed production from 87 of the leading global food crops is dependent upon animal pollination, while 28 crops do not rely upon animal pollination. However, global production volumes give a contrasting perspective, since 60% of global production comes from crops that do not depend on animal pollination, 35% from crops that depend on pollinators, and 5% are unevaluated.“

    So, both talk about 35%, but Dixon makes it „35% of crop value“, whereas the original study very clearly speaks of 35% global production volumes. Though obviously related, they need not be the same thing. But it seems – to me, at least – that this study actually settles it: Approximately one third of the global production volume of food crops is depending on animal pollinators.

    I do not know if they included crops used as animal feed, though…

    • Excellent work, Kerstin! Even though the animal production question is not clear, those are the closest things to real numbers I’ve seen. I think we can accept the one-third number without losing too much sleep over it.

      I will definitely read the supporting papers. I’ve been a fan of Clare Kremen’s work for quite a while, so I’m surprised I missed the info in that particular paper.

      Thank you for your hard work and for making an excellent contribution to this website. Keep me posted on your film so I can let my readers know.

  • Rusty, I am quite glad to have found some answers, too. It always motivates if you are not the only one with a problem…
    I just posted a little blog-entry over at our film-blog MoreThanHoney. You’re in it too 🙂
    More news about the film you can find both there and on Twitter.

  • There are crops that honey bees benefit from, and there are crops that benefit from honey bees.

    Most crops, however, don’t need a single honey bee. But with a few high-value crops (like almonds) the larger the acreage, the more the honey bee is needed for pollination. The reason is that large numbers of honey bees make it possible to farm large acreages of certain high-value monoculture crops. Without honey bees it would be uneconomical to grow these monoculture crops, because there would not be enough natural or native pollinators to go around, especially in the short time the flower is susceptible to pollination.

    Human- or hand-pollinated fruits, by the way, are better formed and in countries like Japan they bring quite a premium, mainly because of their beauty. If it were about crop value it would be impossible to pay a Japanese pear farmer to keep bees on his land. A human with an ostrich feather does a better job pollinating pears than a bee ever can. Also because pears require a cross pollinator species and these species take up space in the orchard that could support a producing tree, 25% more pear bearing trees can be planted in a hand-pollinated orchard. In Japan hand-pollinated Asian pears fetch as much as $11.00 PER FRUIT!

    Honey bees actually detest many veggie pollens and when bees work these crops it is on a do or die basis. The 33% figure first jumped out of thin air back in 1976 and is attributed to S. E. McGregor. There is no evidence at all that this percentage is correct. The actual number is closer to 5%.

  • Keith – not contradicting the validity of your figures. This is purely anecdotal. I raise chemical-free vegetables for a local farmer’s market, including squash, tomatoes, chiles and eggplant. This year for the first time since buying my farm in 1988, I have 8 beehives on site. And I do not think it is coincidence that this year, with extreme heat and drought, nonetheless the fruit set rate for the above mentioned crops is around four- or five-fold over previous years. While working in the pollination-dependent crops, there is a constant low pitched hum of calm foraging bees similar to what I hear out in the clover.
    If they don’t really like those particular veggies, they certainly are womanfully hiding it and shovelling in the pollen. Your use of the term “detest” is suspect: if the pollen really were unpalatable, wouldn’t they avoid it?

    BTW those $11 hand-pollinated pears sound to me more a reflection of economic inequity than a measure of fruit quality. I.e. cheap labor + self-indulgent wealth?

    • An $11.00 pear is an indication of Asian, especially Japanese culture. The “perfect” fruit is where it’s at in Japanese culture. In Japan they even grow square or cube shaped water melons. All the better to fit the interior of your refrigerator. Japan BTW is not exactly a cesspool of low cost coolie labour. [Sentence deleted]

      By hand pollinating pears there are only a very few cross pollinator (male) trees needed. This frees up anywhere from 20% to 40% more land to plant high fruiting (female) trees resulting in much more fruit.

      If $11 pears sound like economic inequity to you, what in the Sam Hill is, “I raise chemical-free vegetables for a local farmer’s market, including squash, tomatoes, chiles and eggplant.” Your truck farm sounds like economically inequity on steroids if you ask me. [Sentence deleted]

      • Keith,

        I value and encourage differing opinions, but personal insults to other readers don’t cut it. Clean it up or don’t submit.

  • Nancy, show me a video of honey bees working tomatoes. There is a lot of tomatoes grown in green houses but a green house will quickly KILL every honey bee in it. The reason for this is that the bees can not orient themselves to the Sun because of the light refraction so they are unable to find their way back to their hive and all the honey bees in a tomato growing green house end up beating their brains out on the inside of the green house roof in a futile attempt to find their hive. This is so whether the hive is inside or outside the green house.

    Besides, tomatoes are self fertile but you can help pollinate them in a green house setting by shaking the plants with a wind machine, or by paying a boy or girl to “gently” shake the vines or to strike them lightly but often with a rod. You have evidently not grown as many veggies as you think you have. If however you wish to grow an award winning ‘mater’ pull off most of the suckers and when the first blossoms opens gently “tickle” the stem holding the flower with a vibrating sex toy. The results are gratifying.

    Dry weather is healthy growing weather for tomatoes, at least if they are irrigated. There is much less bloom end rot and other tomato diseases in dry weather, so your increased fruit set is likely the result of better growing conditions.

    The bees are often more interested in squash nectar than pollen, if you watch carefully you can see honey bees REMOVIMG the pollen of many melon or squash species from their bodies, but even this can help pollinate the plant. The problem comes when there is something growing nearby that the bees like better. In that case they may completely ignore your squash for a weed or even the spilled soda in the trash can at a convenience store. Besides Nancy, what part of do or die are you unfamiliar with. I bet that you’ll eat a lot of things you find repulsive (or feed them to your children) if you or your young are starving. What makes a bee any better than you?

  • Keith,

    Where to start? (Rusty! Help!)

    I don’t grow tomatoes in a greenhouse: that is not sustainable. I also don’t irrigate, relying on deep-planting and heavy mulch to beat drought. I have gardened for 54 years, and grown for Market for 17. This was neither the best nor the worst weather in that span of years, and the pollination is indisputably better. Locally we had been seeing fewer honey bees for around 20 years. I am very grateful for the presence of these hives. Onwards…

    True: there are more bumble bees than honey bees among the tomatoes, but that should just increase our solicitude for our pollinators. The tomatoes are interplanted with tomatillos, and the honey bees are in those for sure, with similar results. And the peppers are the best ever. Weeding or harvesting, I know the buzz of a honey bee from a bumble bee, wood bee or small wild bee.

    Now about squash. Yes, I have seen (photographed!) a honey bee frantically brushing squash pollen off her thorax and not packing it into her corbiculae. She clearly didn’t like it and didn’t think those back at the hive would either. But SO WHAT? She was pollinating the squash. I have also seen as many as 5 honey bees in a male zucchini blossom, which apparently hold a vat of nectar. Who cares whether they’re there for pollen or nectar, the effect is the same.

    In what seems to be your haste (or a rather puzzling imperative) to debunk or denigrate the role of honey bees in agriculture, you may not be considering some alternative modes of growing. My colleagues and I are hands-on, kneel-down, muscle-powered DIRT gardeners. Science starts with observation, not reading sources and theorizing. All I have are my observations, but I darn well do know them!

    I make a point to learn the identity of weeds – among other things, I teach non-chemical weed control – and their relationships to crop species. I know that the bees are in the squash plot, and on the chicory in the fallow plot next to it (I also forgot beans) and down the hill in the goldenrod at the edge of the pasture. My friends in the next country REQUIRE hives for their large soft-fruit operation. After my last post, it occurred to me that bees pollinate major pasture species such as clover, alfalfa, vetches and lespedeza, which are critical to soil improvement, as well as to raising food animals sustainably. And the preceding discussion was limited to human food crops.

    Finally, I am sure bees are better than me at many things. But your use of the word “better” is puzzling: what is bad about eating less desirable foods to fend off starvation? In any case, again, SO WHAT? Your original contention was that bees are not that critical to food agriculture. If they will forage stuff they don’t even like, they’re even more important than we thought.

    Glad to have the discussion with you, but I am afraid most of your arguments proved my point. Thanks!


  • And Keith – how do I “not grow as many vegetables” as I think I have? I know how many I sell! Make your points without questioning my success.

    And – thank you for the advice – I DO know how to prune tomato blossoms for better fruit set, but I do not grow for size only. With paste, cherry and saladette tomatoes, pruning is irrelevant. And the word “‘mater” is condescending to Kentucky people.

    Last, your reference to sex toys is offensive.

    • Nancy,

      The vibrators that Keith refers to are commonly used in greenhouse tomato production for buzz pollination. The vibrator is held against the main stem and shatters the pollen from the flowers. Apparently the frequency closely resembles that of the bumble bee, the primary pollinator of tomatoes.

  • Rusty –


    Well, he’s the one that called them a sex toy. Anyway with bumble bee pollination, outdoors, I have as many tomatoes as I can sell. Thanks,


  • Hi all, I’ve read all your differing opinions with great interest as I’m trying to understand the whole pollination issue better. Although it’s an old discussion, here’s my thoughts on it: I believe the difference in percentages of crops we ‘owe to insects’ (‘Keith’s 5% vs Nancy / Rusty 33%’) may be linked to whether or not the self-pollinated crops (peas, beans etc) are included. Should we include them? I think we do. Although self-pollinating crops don’t strictly need pollinating insects to produce seed, they do benefit greatly from being cross-pollinated by insects. Self-pollination alone will lead to loss of vigor and there is no genetic variety. Self-pollination is often used as a ‘last resort’ by the plant, occuring only at the end of the flowering season in the absence of pollinators. If pollinators are around, peas and beans produce more, healthier crops but in their absence they are still able to produce some peas and beans. Then there are cross-pollinated plants that use both wind and insect pollination, like oilseed rape. An Irish study found that oilseed rape seed production is greatly increased in the presence of pollinators yet it still produces seed when they are absent. All in all I think there is a large grey area of crops that benefit from but not strictly rely on pollinators, which makes it hard to quantify what percentage is actually insect-pollinated.

    • Anneke,

      That is an excellent analysis and I agree with you. Many, many plants benefit from animal pollinators even when they are not dependent on them, and yields of self-pollinating crops are routinely higher when animal pollinators are present.

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