INSECT POLLINATION OF CULTIVATED CROP PLANTS

ECONOMICS OF PLANT POLLINATION

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.

In addition, the insect-pollinated legumes have the ability to collect nitrogen from the air, store it in the roots, and ultimately leave it to enrich the soil for other plants. Without this beneficial effect, soils not fertilized by processed minerals would soon be depleted and become economically unproductive.

Another value of pollination lies in its effect on quality and efficiency of crop production. Inadequate pollination can result not only in reduced yields but also in delayed yield and a high percentage of culls or inferior fruits. In this connection, Gates (1917) warned the grower that, "he may fertilize, and cultivate the soil, prune, thin and spray the trees, in a word, he may do all of those things which modern practice advocates, yet without his pollinating agents, chief among which are the honey bees, to transfer the pollen from the stamens to the pistil of the blooms, his crop may fail."

With ample pollination, the grower may also be able to set his blooms before frost can damage them, set his crop before insects attack, and harvest ahead of inclement weather. Earliness of set is an often overlooked but important phase in the crop economy.

The value of pollination on the succeeding generation of crops is also frequently overlooked. The value of hybrid seed is not reflected until the subsequent generation. Vigor of sprouting and emerging from the soil is often a vital factor in the plant's early survival. Other responses to hybrid vigor include earliness of development, plant health,and greater production of fruit or seed.
__________
¹ The year in italic after the author's name refers to Literature Cited at the end of each major section.

There are numerous ways a grower, with little or no intimate knowledge of the life and habits of pollinating insects, can measure the effictiveness of the polllination of his crop. He would be wise to determine these ways in connection with the particular

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compact clusters of fruits or seeds, and uniform set. For example, adequate pollination is indicated by two or more muskmelons near the crown or base of the vine, or a majority of the apples developing from the king, or primary flower, at the tip of the cluster. In a watermelon field, adequate pollination would be indicated by a high percentage of melons in the number 1 class, that is, symmetrical, completely developed throughout, and of satisfactory weight.

The value of insect pollination, the only type of pollination upon which man can exert much influence, is not limited to the cultivated crops. Bohart (1952*)² pointed out that the most drastic effect of the absence of pollinating insects would be in uncultivated areas, where, as a result, most soil-holding and soil-enriching plants would die out. He also mentioned that springtime would be bleak indeed without the usual gay flowers.

Baker and Hurd (1968) also recognized this important ecological relationship, for they stated that "insect pollination is still extremely important among the fortes of the grasslands, in the shrub and herb layer of the temperate forest and in the desert. It remains undiminished in the tropics."

A simultaneous warning of disaster was recently issued because of our disregard of the importance of pollination. Abelson (1971) stated, "We have developed extraordinarily productive farm crops, but monoculture and the use of limited strains of plants makes the food supply vulnerable to plant enemies such as the southern corn leaf blight." He reminded us that plants are constantly involved in complex chemical warfare not only with pests but also with each other. The slightest weakening may give the enemy the advantage. Likewise, Harlan (1971) reminded us that "The post-modern era has seen spectacular increases in yield, and a virtual genetic wipe-out, with whole continents planted to one or a few related populations. These narrow genetic bases and loss of gene pools are invitations to disaster." Cross-pollination can be one means of preventing such a disaster. This vulnerability to disaster was enlarged upon by Horsfall et al. (1972), who cited such examples as the chestnut blight at the turn of the century, the Bengal famine of India in 1943, and the Irish famine of the 1840's.

The somewhat related warning by Tinker (1971) that one plant species in 10,000 or 20,000 species faces extinction is indicative of the growing problem of a continual adequate food supply of the pollinators. That such changes are actually having an impact on pollinators now was pointed out by Oertel (1966). He maintained certain colonies of honey bees on scales at Baton Rouge, La., and recorded the gain or loss in weight throughout the season from 1929 to 1963. His data (table 2) showed that over the years the weight of the colonies decreased from an average gain of 7 pounds to an average loss of 24 pounds during the period September to November. This loss, he deduced, was related to weed sprays, better pasture care that in general reduced the fall honey flow from goldenrod, a reduction in cultivated crops attractive to bees, along with increased plantings of soybeans that are relatively unattractive, and urbanization. Similar reports from commercial beekeepers across the continent are common. Oertel (1966) stated that lack of an adequate fall crop of honey caused the colonies to be less productive the following spring. According to Wearne et al. (1970), this decreased pasturage was also associated with bee losses.

Hawthorn and Pollard (1954,* p. 56) related this detrimental effect on colony condition to our costs of vegetables when they stated:

In recent years there has been an increasing accumulation of data to indicate that seed yields of insect-pollinated crops may often be lower than they need be, not because of climate, soil, or cultural factors, but simply because the population of certain insects is low.

With a planting of many acres there may not be enough insects such as honey bees to visit the millions of flowers normally present. Even native pollinating insects may be somewhat scarce because the very activity of preparing and cultivating such a large area of land may have destroyed some of their nesting places. Finally, to control some injurious insect the operator may have sprayed the entire planting with an insecticide which has killed many beneficial insects as well as the harmful ones.

Such action is reflected in the economy of beekeeping, as pointed out by Crane (1972) who stated:

In many parts of the world beekeeping hangs in the balance and the scales are tipped against the bees and the beekeepers. . . the very change in land use which now seems to be bringing about the end of beekeeping may lead to its recognition as an essential part of agriculture, because of its importance for crop production.

TABLE 2.--Average gains ( + ) or losses ( - ), in pounds, for colonies (of honey bees) on scales for 5-year periods between 1929 and 1963, Baton Rouge, La.1 _______________________________________________________ _________________________

Years        July      August      September      October      November 
________________________________________________________________________

1929-33      +14        -1          -16             +32           - 9

1934-38      +11        -5          - 7.6           +17.6         - 6

1939-43      +13        -4.4        - 9             +18.4         - 8

1944-48      +38        -4          - 8.5           + 2           - 6

1949-53      +38       2+11         - 7.6           + 2.5         -
10

1954-58      +11        -11.4       -11.2           - 5.3         - 8

1959-63      +21        -11         -14             - 4           - 6

________________________________________________________________________

¹ Source: Oertel (1966).

² A net gain of 50 pounds in August 1950 was responsible for this exception to the usual August losses. An average net gain of 312 pounds was obtained in 1950: net gains were recorded each month from March to October.

Bruner (1966) studied the purely business aspect of vegetable production in northwest Mexico. He noted that the weakness of the "Mexican dictatorial-paternalistic method of farm operation" precluded obtainment of the best technically trained men and new ideas. Bruner considered the lack of proper "saturation-pollination" by bees and protection of beneficial insects from pesticides to be two major reasons for low agricultural production in certain areas. Some larger operations in our country tend to fall into a similar category.

Farms are likely to continue to increase in size because of increased efficiency of operations. Blosser (1960) showed that the average cost of crop production on 640-acre farms was 9.5 to 15.1 percent less than on 160-acre farms that were producing the same crops.

Swift³ reported on the impact of a changed pest control program on the insect pollinators and indirectly on the community. Because of the DDT residue in milk, the California Pest Control Program was changed to include numerous other insecticides, which were much more toxic to honey bees than DDT. The impact of this change was disastrous to the honey bee industry, with 40,000 to 80,000 colonies killed annually. The indirect result was that in 1968 the almond growers, who depend upon honey bees for the pollination of their almond crop, were short at least 26,000 colonies. Swift pointed out that this change to protect the milk had an unanticipated adverse effect on beekeeping, an industry not associated with the dairy industry, and this in turn affected the almond producers, who were still less associated. Swift further pointed out that California crops, valued at $300 million, were dependent upon insect pollination, primarily by honey bees.

The value of insect-pollinated crops in the United States was reported by Metcalf and Flint (1962) to be $4.5 billion. Crops dependent upon insect pollination were valued by Levin (1967) at $1 billion, with additional crops benefited by bee pollination valued at approximately $6 billion. The honey and beeswax produced were valued at about $45 million. In other words, honey bee colonies are worth roughly 100 times as much to the community as they are to the beekeeper.

The aesthetic value of pollination to ornamentals, wild flowers, and forest and range plants in terms of beauty of the landscape is recognized for specific plants (Alcorn et al. 1962, Grant and Grant 1965, McGregor et al. 1962, and Meeuse 1961*) and in general (Kerner 1896-97*, and Knuth 1906-09*), but it cannot be measured. Nor can we measure the related ecological value in terms of seeds, fruits, and nuts produced, which are used as food for various forms of wildlife, but this value, too, is doubtless considerable.

Pollinators other than honey bees are also extremely valuable although their value is difficult to estimate. Within recent years, a few insect species have been managed by man for their pollination service. Bohart (1962*) estimated that the value of the wild bee industry was well over $1 million per year in terms of expenditures and benefits. It had expanded considerably by 1972. No doubt numerous other unmanaged and generally unrecognized wild bees exceed Bohart's estimate. He dealt largely with the gregarious leafcutter bee (Megachile pacifica Panzer),4 and the equally gregarious alkali bee (Nomia melanderi Cockerell). Bumble bees are excellent, although generally unmanageable, pollinators (Holm 1966). Unfortunately, in many intensively cultivated areas, they have largely been eliminated.

² The year in italic followed by an asterisk indicates that the publication is cited numerous times, but the complete citation is given only once in the General Literature Cited, p. 382

³ SWIFT, J. E. UNEXPECTED EFFECTS FROM SUBSTITUTE PEST CONTROL PROGRAMS.
Presented at a symposium on The Biological Impact of Pesticides in the Environment, Oreg. State Univ., Corvallis, Aug. 18-20,1969,16 pp. 1969. (Mimeographed.)

⁴ Formerly known as M. rotundata Fabr. (Holm and Skou 1972).

In a study of the beekeeping industry, Anderson (1969) concluded that the decline in the number of colonies of honey bees from 5.9 million in 1947 to 4.8 in 1966 was attributable to the low rate of return on the invested capital. Some beekeepers have tried to increase production by moving their colonies from one honey flow to another, a practice started as early as 1895 (Zierner 1932). At that time, apiaries in California were moved by wagon from the desert sage and wild buckwheat to the cultivated lima bean fields. Today, thousands of colonies are moved hundreds of miles each year to several different floral sources. Anderson reported that others have tried to supplement their honey sales through the placement of their colonies in fields for pollination, but few could indicate that a profit was made.

If the need for insect pollination is increasing, one would assume that the number of colonies of honey bees should also be increasing to help meet this demand. Such is not the case. The number of colonies in the United States has been decreasing steadily for more than two decades. Furthermore, in contrast to earlier recommendations that every farm keep a few colonies of bees (Tyler and Haseman 1915), the colonies are no longer present on almost every farm. They have either shifted to the suburbs, where they are operated by hobbyists who have short workweek employment, or they are operated by large-scale commercial beekeepers. This situation has disturbed the more or less even distribution of pollinators across the countryside, and even created a serious deficiency in some areas.

In some instances, this lack of an adequate supply is made up by the beekeeper renting colonies to the grower. An estimated 1 million colonies are rented for pollination of crops in the United States annually (there are no concrete figures on the number of such colonies). In some instances, the rental fees are no greater than those of five decades ago. There are several reasons for such low fees. There is almost no organized use of bees for pollination. Each beekeeper sets his own price. Sometimes the bees are supplied almost as a favor in exchange for apiary locations throughout the year, or for favorable consideration in relation to pesticides applied near the bees. The beekeeper may be hesitant to ask for higher fees for fear another beekeeper might undercut his price or move into his "territory."

Unfortunately, when the beekeeper operates the colonies at a low pollination fee, he tries to make up his fee elsewhere--a practice that may not be to the best interest of the grower. An inadequate number of colonies for maximum pollination may be supplied, the colonies may not contain the desired population of worker bees, or they may not be appropriately managed or distributed throughout the field to be pollinated.

A population of bees necessary for maximum set of fruit or seeds on the crop may be far greater than the location will support for honey production or colony maintenance.

There appears to be a potential market for many more properly maintained and managed colonies of honey bees for pollination of present and anticipated crops than can be mobilized. However, the beekeeper is reluctant to go to the extra expense and labor of moving his colonies into an overstocked area unless he can collect an adequate fee for his trouble and have some assurance that the colonies will not be damaged by pesticides. He frequently finds himself in no position to bargain for these considerations. This points up the need for an organized pollination service staffed by experts acquainted with the needs and problems of both the grower and the beekeeper and capable of bargaining fairly for both. (See "Pollination Agreements and Services.")

ABELSON, P. H.
1971. OPPORTUNITIES IN PLANT SCIENCE. Science 172(3989): Editorial page, no page number.

ALCORN, S. M., MCGREGOR, S. E., and OLIN, G.
1962. POLLINATION REQUIREMENTS OF THE ORGAN-PIPE CACTUS. Cactus and Succulent Jour. 34: 134 - 138.

ANDERSON, E. D.
1969. AN APPRAISAL OF THE BEEKEEPING INDUSTRY. U.S. Dept. Agr., Agr. Res. Serv. ARS 42-150,38 pp.

BAKER, H. G., and HURD, P. D., JR.
1968. INTRAFLORAL ECOLOGY. Ann. Rev. Ent. 13: 385-414.

BLOSSER, R. H.
1960 SIZE OF FARM AFFECTS CROP COSTS. Ohio Farm and Home Sci. 45(6): 92--93.

BRUNER, J. .M
1966. MANAGEMENT--A STRATEGIC AGRICULTURAL RESOURCE. Ariz. Business Bul. 13(10): 10 - 18.

CRANE, E.
1972. BEEKEEPING IN THE BALANCE.[Editorial.] Bee World 53: 3 - 4.

GATES, B. N.
1917. HONEY BEES IN RELATION TO HORTICULTURE. Mass. Hort. Soc. Trans. 1: 71-88.

GRANT, V., and GRANT, K. A.
1965. FLOWER POLLINATION IN THE PHLOX FAMILY. 180 pp. Columbia University Press, New York and London.

GUIDRY, N. P.
1964. GRAPHIC SUMMARY OF WORLD AGRICULTURE. U. S. Dept. Agr. Misc. Pub. 705, 64 pp.

HARLAN, J. R.
1971. GENETICS OF DISASTER. Agron. Abs., Ann. Mtg. Amer. Soc. Agron., p. 7.

HOLM, S. N.
1966. THE UTILIZATION AND MANAGEMENT OF BUMBLEBEES FOR RED CLOVER AND ALFALFA SEED PRODUCTION. Ann. Rev. Ent. 11: 155 - 182.

and SKOU, J. P.
1972. STUDIES ON TRAPPING, NESTING AND REARING OF SOME MEGACHILE SPP., (HYMENOPTERA, MEGACHILIDAE) AND ON THEIR PARASITES IN DENMARK. Ent. Scand. 3: 169-180.

HORSFALL, J. G., BRANDON, G. E., BROWN, W. L., and others.
1972. GENETIC VULNERABILITY OF MAJOR CROPS. 307 pp. Natl. Acad. Sci., Washington, D. C.

LEVIN M. D.
1967. POLLINATION. In Beekeeping in the United States, U. S. Dept. Agr., Agr. Handb. 335, pp. 77-85.

MCGREGOR, S. E., ALCORN, S. M., and OLIN, G.
1962. POLLINATION AND POLLINATING AGENTS OF THE SAGUARO. Ecology 43: 259-267.

METCALF, C. L., and FLINT, W. P.
1962. DESTRUCTIVE AND USEFUL INSECTS. Ed. 4, 1087 pp. McGraw-Hill Book CO. Inc., New York and London.

OERTEL, E.
1966. OUR CHANGING AGRICULTURE REQUIRES CHANGES IN BEEKEEPING.Amer. Bee Jour. 106: 401-408.

THURSTON, H. D.
1969. TROPICAL AGRICULTURE- A KEY TO THE WORLD FOOD CRISIS. Bioscience 19: 29-34.

TINKER, J.
1971. ONE FLOWER IN 10 FACES EXTINCTION. New Scientist and Sci. Jour. 50 (751): 408-413.

TYLER, E. E., and HASEMAN, L.
1915. FARM BEE-KEEPING. Mo. Agr. Expt. Sta. Bul. 138, 40 pp.

WEARNE, R. A., BERGMAN, P., GIBBS, L. C., and others.
1970. BEE LOSSES--THE IMPACT ON POLLINATION--HONEY PRODUCTION. U.S. Dept. Agr. Ext. Serv., 12 pp.

ZIERNER, C. M.
1932. MIGRATORY BEEKEEPERS OF SOUTHERN CALIFORNIA. Geog. Rev. 22: 260 - 269.