Probably the most important activity of bees, in terms of benefits to humans, is their pollination of natural vegetation, something that is rarely observed by nonspecialists and is almost never appreciated; see Section 6. Of course the products of honey bees—i.e., wax and honey plus small quantities of royal jelly—are of obvious bernefit, but are of trivial value compared to the profoundly important role of bees as pollinators. Most of the tree species of tropical forests are insect-pollinated, and that usually means bee-pollinated. A major study of tropical forest pollination was summarized by Frankie et al. (1990); see also Jones and Little (1983), Roubik (1989), and Bawa (1990). In temperate climates, most forest trees (pines, oaks, etc.) are wind-pollinated, but many kinds of bushes, small trees, and herbaceous plants, including many wild flowers, are bee-pollinated. Desertic and xeric scrub areas are extremely rich in bee-pollinated plants whose preservation and reproduction may be essential in preventing erosion and other problems, and in providing food and cover for wildlife. Conservation of many habitats thus depends upon preservation of bee populations, for if the bees disappear, reproduction of major elements of the flora may be severely limited.
Closer to our immediate needs, many cultivated plants are also bee-pollinated, or they are horticultural varieties of bee-pollinated plants. Maintenance of the wild, bee-pollinated populations is thus important for the genetic diversity needed to improve the cultivated strains. Garden flowers, most fruits, most vegetables, many fiber crops like flax and cotton, and major forage crops such as alfalfa and clover are bee-pollinated.
Some plants require bee pollination in order to produce fruit. Others, commonly bee-pollinated, can self-pollinate if no bees arrive; but inbreeding depression is a frequent result. Thus crops produced by such plants are usually better if bee-pollinated than if not; that is, the numbers of seeds or sizes of fruits are enhanced by pollination. Estimates made in the late 1980s of the value of insect-pollinated crops (mostly by bees) in the USA ranged from $4.6 to $18.9 billion, depending on various assumptions on what should be included and how the estimate should be calculated. Also doubtful is the estimate that 80 percent of the crop pollination by bees is by honey bees, the rest mostly by wild bees. But whatever estimates one prefers, bee pollination is crucially important (see O'Toole, 1993, for review), and the acreages and values of insect-pollinated crops are increasing year by year.
Wild bees may now become even more important as pollinators than in the past, because of the dramatic decrease in feral honey bee populations in north-temperate climates due to the introduction into Europe and the Americas of mites such as Varroa and tracheal mites, which are parasites ofhoney bees. Moreover, there are various crops for which honey bees are poor pollinators compared to wild bees. Examples of wild bees already commercially used are Osmia cornifrons (Radoszkowski), which pollinates fruit trees in Japan; Megachile rotundata (Fabricius), which pollinates alfalfa in many areas; Bom-
bus terrestris (Linnaeus), which pollinates tomatoes in European greenhouses, and other Bombus species that do the same job elsewhere. O'Toole (1993) has given an account of wild bee species that are important in agriculture, and the topic was further considered by Parker, Batra, and Te-pedino (1987), Torchio (1991), and Richards (1993). Since honey bees do not sonicate tubular anthers to obtain pollen (i.e., they do not buzz-pollinate; see Sec. 6), they are not effective pollinators of Ericaceae, such as blueberries and cranberries, or Solanaceae such as eggplants, chilis, and tomatoes.
Many bees are pollen specialists on particular kinds of flowers, and even among generalists, different kinds of bees have different but often strong preferences. Therefore, anyone investigating the importance of wild bees as pollinators needs to know about kinds of bees. The classification presented by this book can suggest species to consider; for example, if one bee is a good legume pollinator, a related one is likely to have similar behavior. Proboscis length is an important factor in these considerations, for a bee with a short proboscis usually cannot reach nectar in a deep flower, and probably will not take pollen there either, so is unlikely to be a significant pollinator of such a plant.
Although some bees, e.g., Euglossini and many Meliponini, inhabit undisturbed forests, especially in the tropics, many and probably most bee species inhabit savannas and forest margins and thrive in moderately disturbed areas. Temperate forests were presumably never good places for most bees since they consist largely of trees that do not produce flowers visited by bees. There were probably fewer bees in primeval temperate forests than now inhabit the same areas. Now, with pastures, waste lands, road and field margins, and forests that have been opened by cutting, once scarce species of bees have become abundant and presumably play important roles as pollinators of the vegetation. Even unbroken prairie appears to have fewer bees than more or less abandoned disturbed areas. Thus Laroca (1983) found more species and individuals in a little used, often disturbed university campus area, not planted with lawn or other vegetation, than in nearby prairie in Kansas. Of course the bees in such areas are the species that may pollinate agricultural crops or ornamental plants and, therefore, may be selected for practical use as pollinators.
Although disturbed areas often have more bees than undisturbed areas, it does not follow, of course, that the more disturbance, the better for the bees. When a whole area becomes a monoculture of corn or any other crop, most bees become dependant on small waste areas or road verges, and with small isolated populations, the number of species and individuals will soon be reduced.
In many countries the populations of wild bees have been seriously reduced by human activity. Destruction of habitats supporting host flowers, destruction of nesting sites (most often in soil) by agriculture, roadways, etc., and overuse of insecticides, among other things, appear to be major factors adversely affecting wild bee popula tions. Introduction or augmentation of a major competitor for food, the honey bee, has probably also affected some species of wild bees. Recent accounts of such problems and some possible solutions were published by Banaszak (1995) and Matheson et al. (1996); see also O'Toole (1993).
National and international organizations are now seriously considering and publicizing the need to conserve native pollinators (mostly bees) to maintain agricultural production as well as survival and well-being of native vegetation. Recent accounts of pollination problems worldwide have been included in numerous reports; see Kevan and Imperatriz-Fonseca (2002) and Freitas and Pereira (2004).
A single example analyzing the economic impact of bees (Apis and Meliponini) on a 1,065-hectare coffee plantation (this crop does not even require insect pollination) is telling. Bees from two forest fragments (46 and
111 hectares) translated into ~US$60,000 per year added income for the farm (Ricketts et al., 2004). Another relevant work is Imperatriz-Fonesca, Saraiva, and De Jong (2006). A useful bibliography for the neotropics is Anonymous (2006).
One ofthe problems in verifying recent declines ofpol-linating insects has always been lack of firm quantitative data on abundance in times past. Collectors' recollections and museum specimens suffice for presence (and even absence) information, but not for changes in abundance. A recent study (Biesmeijer et al., 2006) in The Netherlands and United Kingdom, however, compares older (before 1980) versus recent (after 1980) data and shows substantial declines in local bee diversity, in particular, declines of oligolectic and other specialist species, and parallel declines in plant species dependent for pollination services on such bees.
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