Pollination, The Forgotten Agricultural Input
by
Dr. Malcolm Sanford
Introduction:
Research over the last few decades has enabled agriculturists to make great strides in both quantity and quality of food and fiber produced. The amount of fertilizer, water, sunlight and other variables such as proper cultivation, weed management and pesticide application are well known for many cultivated crop varieties. One input, however, has often been left out of the process, pollination, the vital reproductive process of plants. This is easy to understand because pollination is extremely complex and often occurs in an open system with variables that are difficult to control. As a consequence a myth has been perpetuated that in many cases pollination will take care of itself.
Only in a few crops do we know for certain that pollination is absolutely essential for large-scale fruiting. The most striking is the almond crop. The need for pollination is so intense that hundreds of thousands of honey bee colonies are moved into each year, sometimes from as far away as , just to attend to this vital function. Honey bees are extensively used in other crops, including apples, cranberries, blueberries, kiwifruit and cucurbit or vine crops. To a minor extent they are also used to pollinate strawberries, peppers, peaches, pears, plums and citrus. Finally, these insects are extensively employed in producing carrot, onion and other seed crops. It is estimated over 90 crops are benefited by honey bee pollination and the value of this service to the agriculture has been estimated to be about 18 billion dollars!
Because honey bee use is so universal, it is easy to be lulled into another myth. Honey bees are the best pollinators for almost all crops. This implies that these insects are somehow the most efficient pollinators. This is not the case. Because the honey bee is a cosmopolitan pollinator, it is not a specialist for many of the plants it visits. In addition, it is an introduced species into North America and as such has not co-evolved with plants native to the .
Perhaps the best example of a more efficient insect is the alfalfa leafcutter bee (Megachile rotundata). This alternative pollinator generates several million dollars of value each year. Other bees in common use are bumblebees (Bombus sp.), the imported hornfaced bee (Osmia cornifrons) and the domestic blue orchard bee, Osmia lignaria. Other specialist bees, sometimes referred to as “pollen bees,” also exist. One, the southeastern blueberry bee (Habropoda laboriosa), is a specialist on that native plant; the squash bee (Peponapis sp.) is found in close association with cucurbit or vine crops.
The purpose of this article is to describe commercial pollination using honey bees and compare and contrast that enterprise with one using alternative pollinators in specific situations. Research needs will also be identified to better determine what pollinator might be best under certain conditions. This will help agriculturists come to grips with the forgotten input, crop pollination
Honey Bee: The Insect of Choice in Most Agricultural Situations:
The honey bee (Apis mellifera) is the insect of choice in most managed commercial pollination. It has significant advantages over other insect pollinators because it is social and develops large populations that become a significant pollinating force. In addition, the technology exists to augment population numbers and move honey bee colonies quickly and efficiently. This not only helps growers, but also protects the insects and beekeeper from damage when pesticides must be applied. Finally, there continues to be evidence that in some cases, honey bees can be attracted to crops through chemical means.
The cosmopolitan nature of the honey bee is also an important characteristic. It will pollinate a wide variety of crops. Over 90 have been identified in and over 300 worldwide. In the , the honey bee’s value as a pollinator has been estimated to be as high as $18 billion to as low as $1.8 billion, depending on how the calculation is made. Perhaps the family of commercial plants for which honey bee pollination in most important is the curcurbit or vine crops.
In the past, growers could often get colonies of honey bees relatively inexpensively. In some situations, if the crop produced abundant nectar, beekeepers would even pay to move onto the crop. This is probably best illustrated where citrus growers and beekeepers have developed a unique symbiotic relationship. Although generally not recognized because so many bees are located in citrus crops, the honey bee pollinates these plants as well.
Pollination is a growing enterprise and could be exploited by beekeepers in a number of ways, but represents a fundamental change in thinking. The reason for this is that it is a service enterprise, not one of producing and selling a product. For a most efficient pollinating service, beekeepers can unite into cooperatives that specialize in this activity. This, however, has not been a widespread occurrence; in fact, the opposite has often been the case with beekeepers vigorously competing for pollination contracts. In France a cooperation model has been somewhat adopted in seed pollination using brokers or coordinators.
Although known for a long time that honey bees were important pollinators, this was not strongly brought to public attention until introduction of the Varroa bee mite. This introduced parasite has been responsible for eliminating many wild, unmanaged honey bee colonies that provided pollination ancillary to their other activities. Growers and the general public appear to have gotten this message and pollination has, therefore, received more respect and support than previously.
Unfortunately, much agricultural research has focused on the role of other inputs such as fertilizer, water, cultivation and insect control. In the process, that concerning pollination has often been relegated to the back burner. The myth seems to have been perpetuated that pollination would somehow take care of itself. This increasingly seems to be a misguided philosophy. However, to do quality study in this area is extremely complex, time consuming and expensive.
As a testimony to the scarcity of research in this area, the best resource growers and beekeepers can turn to is Insect Pollination of Cultivated Crop Plants, authored by S.E. McGregor and published by the Agricultural Research Service (ARS) way back in 1973.
The economics of using honey bees in commercial pollination has been greatly affected by introduction of parasitic mites and often is predicated on the price of honey, which can result in an unstable supply of this valuable service. In addition, honey bees are not the most efficient pollinators in all situations. They are also an introduced species and cannot be expected to be specialty pollinators of native North American plants. As a consequence, an intense interest in alternative pollinators has recently emerged.
Alternative Pollinators:
Perhaps the largest non-honey bee pollination effort in is that associated with growing alfalfa for seed. Although honey bees continue to be used for this purpose, they are not as efficient as the alfalfa leafcutter bee, Megachile rotundata, which immigrated to North America from in 1935. Although they will forage on alfalfa, over time honey bees learn to almost completely avoid the pollinating mechanism during in the nectar-gathering process. Thus, they become less efficient as time goes by. The alfalfa leaf cutter bee by contrast is more wedded to the plant and thus extremely efficient. In the , a large industry exists rearing this insect strictly for alfalfa seed. The development of this enterprise has many parallels with that using the honey bee. More recently, there is experimentation in using this bee for pollinating other crops such as blueberries . Another alfalfa pollinator is the turquoise-banded alkali bee, native to western (Nomia melanderi), which also can be managed to some degree.
Bumblebees (Bombus sp.) have recently taken on a large role in green house pollination. Honey bees do not orient well in greenhouses. Bumblebees are particularly effective for tomatoes because they “buzz pollinate,” which effectively shakes the pollen loose from the bloom. Bumblebees are not perennial and nests are usually started each year. Therefore, a continuous supply is often necessary to get full pollinating potential. They are, however, native insects and responsible for efficiently pollinating plants. Finally, bumblebees forage at low temperatures, and often when its raining or windy. By contrast honey bees are much more “fair weather” foragers.
Honey bees and bumblebees are social insects, however, literally thousands of species of solitary soil-nesting bees exist that often pollinate specific plants. The term “pollen bees” was coined for these insects in 1992. Examples of these include those associated with pollinating blueberries, squash and other vine crops. The southern specialist on the former crop is the Southeastern blueberry bee (Habropoda laboriosa). Bees in the genus Peponapis most effectively pollinate squash. These insects reside directly in the flowers. Other solitary bees include those variously named “polyester,” “digger” and “mason,” depending on the kind of nesting behavior they exhibit.
The problem with solitary species is that the knowledge to rear these insects and deploy them in a managed agricultural system usually does not exist. Thus, one is forced to rely on Mother Nature to provide them when they are needed and in sufficient numbers. This is an “iffy” process at best, and every growing season is by definition different. The best strategy to maximize populations of soil-nesting bees is to conserve their habitat by providing nesting habitat and installing natural bee pasture.
According to Dr. Suzanne Batra, Beltsville Bee Laboratory (American Bee Journal, Volume 134, No. 9, September, 1994), the first species of pollen bee to be brought into management was the hornfaced bee (Osmia cornifrons). An apple grower, E. Matsuyama in , noticed these small brown bees working his apple blossoms and nesting in nail holes in his wooden house in the 1930’s. Soon he made more nail holes in his house, and as the bees multiplied and his apple crop prospered; he switched to cutting sections of hollow reeds for the bees to nest in. Hornfaced bees pollinate a third of ‘s apples, and their use is spreading in North American and . Their more recently domesticated relatives are the European bees, Osmia cornuta and Osmia rufa, and the native North American mason bee or blue orchard bee, Osmia lignaria
There are many reasons for the rapidly increasing popularity of hornfaced bees and their relatives for pollinating fruit trees, according to Dr. Batra. These include: (1) being active in the spring, before honey bee colonies reach large sizes; (2) preferring fruit flowers, thus staying on the crop; (3) contacting the flowers’ anthers and stigmas on every visit; (4) flying rapidly, thus working many flowers; (5) carrying pollen loosely under the abdomen so it can easily and freely be dispersed; (6) pollinating males; (7) keeping their foraging range short in the orchard; (8) being easily reared; (9) stinging less and having weaker venom; and (10) being able to be stored away between pollination seasons.
Because of their advantages, as few as 80 female hornfaced bees are needed per hectare of apples. Similarly, 300 blue orchard bees per hectare are also enough. In , only 3 Osmia cornuta per almond tree provide adequate pollination. This contrasts sharply with the 2 to 6 hives containing thousands of honey bees recommended per hectare of orchard.
Conclusions:
Honey bees are usually the insect of choice in most managed pollination situations. They are cosmopolitan pollinators, which produce large populations that can be effectively moved when conditions dictate. In some instances they also can be chemically attracted to crops for increased pollination efficiency. Finally, a commercial infrastructure already exists to maximize the honey bee’s pollinating potential. They are, however, not the best insects to use in all situations. This is particularly true where they are an introduced species.
Because insect pollination specialists exist that are far more efficient than honey bees in some situations, there continues to be interest in exploiting these alternative pollinators. Those with management schemes in place include leafcutter and alkalai bees in alfalfa pollination and bumblebees in greenhouses for tomatoes. A wide variety of other bees can be found in the environment that are specialist pollinators. Unfortunately, there is little if any information on rearing and deploying these so-called “pollen bees,” and growers are left with only generalized recommendations on providing nesting and foraging habitat near crops that require pollination. There is a possibility that the future may bring more research knowledge so that these alternative pollinators can be used as is now the case with the hornfaced bees in and elsewhere. In the meantime many insect pollinators are at best overlooked, at worst exterminated in commercial agricultural situations or killed off by environmental degradation.
For both honey bees and solitary bees, research is desperately needed to determine not only the value of their pollination, but also how to most effectively rear and deploy these pollinating insects. Much is known about the panoply of other agricultural inputs, but pollination has often been sidestepped in the process. Only when growers and commercial pollinators get a better picture of the key relationship between certain plants and their pollinators will they be able to take advantage of this forgotten agricultural input.
Literature Cited:
Batra, S. 1994. Diversify With Pollen Bees, American Bee Journal, Vol. 34, No. 9:556-7.
CAPA eds. 1997. A Guide to Managing Bees for Crop Pollination, Canadian Association of Professional Apiculturists.
Delaplane, K. 1998. Bee Conservation in the Southeast, , Cooperative Extension Bulletin 1164.
McGregor, S.E. 1973. Insect Pollination of Cultivated Crop Plants, Agriculture Handbook 496, Agricultural Research Service, July 1976.
