Honey Bee Biology
Honey Bee Biology - December 2014
Honey Bee Pollination with Movie Clips: Following Individual Foragers
by Dr. Wyatt A. Mangum
Beekeepers need to have a clear understanding of pollination, its value to the general public, and the role of native bees in pollination. Along with honey bees, promoting the diversity of all kinds of bees is another way to promote a healthier environment because the number of pollinators are decreasing, while the need for pollination is increasing.
Pollination is the movement of pollen grains from the male flower parts (the anthers) to a special structure typically in the center of the flower with a sticky surface (the stigma) to receive incoming pollen as shown in Figure 1. The two flower parts could be housed in the same flower or separated on different flowers. Pollination is different from fertilization, which is the union of the genetic material from the maternal and paternal plants. After pollination and before fertilization occurs, a pollen tube grows from the pollen grain embedded in the stigma down to the ovary in the base of the flower. The pollen tube provides a passageway for the male plant’s genetic material, released from the pollen grain at the sigma surface, to move down to one of the ovules, a future seed, in the ovary. Within the ovule, male and female genetic material unite, so in the ovule is where fertilization occurs. The fruit we eat grows in response to fertilized seeds from pollination. Notice if pollen tube growth fails, pollination still occurred (the bees did their job), yet fertilization for that particular seed would not occur nor would the corresponding fruit growth resulting from that fertilized seed. Failed fertilization is why other factors, besides poor pollination, can produce lopsided apples and crooked cucumbers. On the other hand, if bees were lacking, a quiet field or orchard, no hum with plants in bloom, and the plants had proper irrigation, fertilizer applications etc., then poor pollination would obviously be the most likely culprit (See Figures 2 and 3).
While most people associate bees with honey, in United States agriculture bees are most valuable as pollinators. In these various crop systems, called agro-ecosystems, honey bee pollination was estimated as $14.6 billion based on an estimate in 2000 (Morse and Calderone, 2000). While that is an old estimate, it is huge compared to U. S. honey production valued on the order of $200 million. That old pollination estimate did not include a new factor, shelf life, which for strawberries was shown to increase substantially with better pollination, adding to its value of the product. It was reported to have a longer shelf life reducing fruit loss by at least 11% accounting for about one-third of a billion dollars ($.32 Billion) when selling U.S. strawberries to the European Union (overseas shipping). Moreover, the strawberry physiology showed that proper pollination helps to preserve the fruit on a chemical level. Therefore on that fundamental chemical level, since pollination helps increase shelf life, then it is reasonable to think similar effects would occur with other insect pollinated crops. So overall from a shelf life consideration, pollination has been undervalued (Klatt et al., 2014). By how much remains unknown. Nevertheless 75% or 87 of 115 of the leading crop plants worldwide depend on, or at least benefit from animal pollination. The remaining 28 crops depend on the wind or are self-pollinated (Klein et al., 2007). Turning from the number of plants to their production amounts, 35% of global crop production is dependent on animal pollination (Klein et al., 2007). (This estimate is very inclusive. So they use “animal” to include all pollinators. A large part of that figure would presumably be honey bees including the Asian honey bee Apis cerana.)
I have seen numerous articles in the popular press stating that one-third of our food or diet depends on honey bee pollination (before we see it in Klein et al., 2007). I also see the statement interpreted as one in three bites of food depend on honey bee pollination. Most likely it is stated in that fashion, to make the fraction, one third, seem less abstract in the popular press, which is reasonable. However, few can find the original source of the one-third pollination statement, meaning the original book and page, where the statement first appeared before later modifications. Well-informed beekeepers should know from where the one-third pollination statement originates since so many people have heard it, and because of its frequency in the press. It has a strong citation history, not like other dubious things said about bees on the web, which need to go away.
For decades, I have had the reference stamped in my mind as “S. E. McGregor 76.” It was in the first book devoted to pollination that I bought: Insect Pollination of Cultivated Crop Plants, Agriculture Handbook Number 496 by S. E. McGregor published in 1976 (McGregor, 1976). The book is 411 pages in a large format with beautiful detailed diagrams of the crop flowers showing the anthers and stigmas. The one-third reference is on page one at the top of the second column. In the estimate, McGregor is also including the plant-based oils and fats (oils like canola, sunflower, etc.) dependent on insect pollination, and other insect-pollinated plants used in animal production:
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.
Notice, no mention of honey bees in the original quote, although they would probably have been the majority pollinator. Nevertheless, McGregor’s original statement appears much different from something like one in three bites of food depend on honey bee pollination (or bee pollination meaning honey bees). While it conveys a targeted message, that overly simplified allusion excludes the other pollinating bee species, not to mention other such insects. In the original, McGregor did not exclude them. (McGregor, 1976 is inclusive like Klein et al., 2007).
For example bumble bees are valuable pollinators. Their importance has grown since the original one-third statement in 1976. Bumble bee colonies are rented out for greenhouse pollination, and wild colonies are extremely valuable pollinators. I have been telling farmers for years to leave bumble bees uncut places for them to nest and forage. I make it clear to the farmer that the wild flowers are probably too meager for my honey bees to accept. That way my advice is not seen as self-serving, which is it not.
After helping to pollinate a farmer’s crop, or being the sole pollinator for plots typically too small for honey bee rental, some wild bees, particularly bumble bees, need a chain of other flowers, blooming sequentially, for a food supply. Mowing all the “waste” places might look golf-course neat, but for these other bees, it sterilizes their food sources causing them starvation, reducing the population of pollinators for next season, and their beneficial effects. Excessive mowing is one form of habitat destruction in my opinion, and a preventable one. I would advise mowing fields in the fall after the wild flowers have bloomed and their seeds are floating away on the wind.
Fast-flying squash bees (most likely Peponapis pruinosa) flit and dart among the flowers of squash and other gourd plants in zillions of gardens. These bees specialize for pollinating squash flowers, ignoring other blooming plants. They only forage in the morning when squash flowers are open, under conditions when honey bees would not touch them. When I ask gardeners about their squash bees, I typically get the speak-English look. Clueless. While their forage is in the garden, provided by the squash flowers, these bees need a place to nest, in undisturbed ground.
Recent research is showing the importance of native bees (non-Apis bees) in commercial pollination. Here is an example of the new behavior being found. California almond production is the major crop requiring honey bee pollination in the U. S. Remarkably, having the solitary bee, the Blue Orchard bee (Osmia lignaria) pollinate along with the dominant pollinator, the honey bee, resulted in more fruit set. Apparently, the Blue Orchard bee changed the honey bee flight making them cross more to different tree rows, and they cross pollinated more instead of just working down the same row of the same variety of tree that cannot self pollinate. The pollen needs to move to a different row, which is a different variety of tree (Brittain et al., 2012).
Now let’s try something brand new – looking at pollination from the honey bee’s point of view. To acquire a firsthand, more intimate, appreciation of honey bee pollination, try watching my movie clips of individual bees foraging from ...