Status of Pollinators in North America (2007) / Chapter Skim
Currently Skimming:
3 Causes of Pollinator Declines and Potential Threats
3 Causes of Pollinator Declines and Potential Threats
Pages 75-103
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) , and the invasive Africanized honey bee.
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. In eastern honey bee colonies, female varroa mites reproduce almost exclusively on male (drone)
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However, except for the large loss of honey bee colonies in the 1940s from the bacterial disease, AFB, losses on this scale were never reported before the detection of parasitic mites (Finley et al., 1996)
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. The current status of the tracheal mite and its impact on honey bees are unknown.
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Pesticides The application of pesticides, especially insecticides used to control crop pests, kills or weakens thousands of honey bee colonies in the United States each year (Johansen and Mayer, 1990)
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The negative impact of pesticides on managed honey bee colonies suggests that feral bee populations could be similarly affected by pesticides, but there are no studies on the latter subject to the committee's knowledge. Feral honey bees have not been studied intensively (see Chapter 2)
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. Several traits have facilitated the establishment of Africanized honey bees: their colonies grow faster than do those of the European honey bees, and there are genetic incompatibilities in hybrids that favor loss of European traits; African drones exhibit mating advantages; Africanized bees have a greater ability to establish nests in a broader variety of locations; and they exhibit more nest usurpation behavior than do European bees (Schneider et al., 2004)
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FIGURE 3-1 Current distribution of Africanized honey bees.
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About half of the queens are produced in the western United States and half in the southeastern United States. Africanized honey bees will also encroach on prime agricultural regions such as the almond orchards in California.
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Bumble Bees (Bombus spp.) Starting in the early 1990s, companies in Europe (Banda and Paxton 1991)
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. The frequency of this disease in honey bees is increasing because of oral transmission and transmission by varroa mites; in bumble bees, transmission appears to be exclusively oral.
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. Like honey bees, bumble bees can be exposed to pesticides while foraging (Gels et al., 2002; Tasei et al., 2001)
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. DECLINE IN NATURAL OR WILD POLLINATORS Pathogen Spillover Nosema bombi could be the most important factor responsible for the extinction of Bombus franklini (Thorp et al., 2003)
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Commercially produced bumble bees used for greenhouse pollination often have extensive pathogen infections that can spread to wild bees when the commercial bees escape from greenhouses and interact with their wild BOX 3-1 Unintended Consequences of Greenhouse Pollination and Native Pollinators When commercial growers began to grow tomatoes in greenhouses, they realized that good fruit set required pollination (Velthuis, 2002)
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. They reported that honey bees lowered the available amount of Agave pollen and nectar, and their introduction led to shifts in the numbers of foraging native bumble bees and nectar-feeding ants.
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Accidental 1930s Megachile concinna Smith Accidental 1940s Megachile lanata (F.) Accidental 1700–1800s Megachile rotundata (F.)
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) Roberts, 1978 Centaurea Eastern United States, Washington, Polylectic Stephen and Torchio, 1961 Oregon, California Transcontinental Asteraceae Butler and Wargo, 1963 Florida Polylectic Mitchell, 1962 Transcontinental Fabaceae Stephen and Torchio, 1961 Eastern United States Polylectic Mangum and Brooks, 1997; Batra, 1998 Northeastern and northwestern Fabaceae Rust, 1974 United States, parts of Canada adjacent to the United States Transcontinental, patchy Rosaceae Batra, 1998 Limited local U.S.
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found that niche overlap between honey and bumble bees reached levels as high as 80 to 90 percent during times of resource scarcity, but only in 1 of 7 months of observation was there a significant negative relationship between them. In an experimental study, however, the mean numbers of bumble bee foragers observed on a given transect increased significantly with greater distance from introduced honey bee colonies.
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Bumble bees seem particularly susceptible to such effects,
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. The apparent loss of two species in the United States in the past few years suggests that North American bumble bees are similarly imperiled as a result of the combined effects of numerous anthropogenic factors, including habitat loss, degradation, conversion, pesticide use, pollution, and pathogen spillover from commercial bumble bee cultures (Thorp, 2003, 2005)
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has recently been identified in honey bees (Beye et al., 2003) , providing strong molecular support for understanding complementary sex determination.
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. Before the 1996 release of Bt corn, most industry testing focused on nontarget predators and the honey bee, all of which are taxa not expected to be affected by the Lepidoptera-specific toxins (Malone and Pham-Delègue, 2001; O'Callaghan et al., 2005)
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fields of GMHT crops, and Haughton and co-workers (2003) reported reduced abundances of butterflies in transgenic beet and spring canola fields and smaller numbers of bees in transgenic beet fields compared with non-GMHT crops.
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. Whether the reduced abundances in the field could lead to reduced pollinator populations over time would depend on the proportion of GMHT crops within the foraging ranges of these insects.
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Natural habitats have been destroyed or fragmented along the migratory corridors of western Mexico and other areas (Valiente-Banuet, 2002) , but it is not known whether the destruction is damaging bat populations.
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and all have experienced severe habitat destruction or fragmentation caused by conversion of grasslands to use for cattle ranching or agriculture. Urban or suburban domestic cats that are allowed outside have been implicated in mortality of ruby-throated hummingbirds, a species of conservation concern in some parts of its range (Lepczyk et al., 2004)
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Stephanou and colleagues (2000) reported that UV-B increased nectary size in another species, which apparently resulted in an observed increase in pollination, but no differences were reported in honey bee foraging behavior on brassicaceous nectar plants exposed to and protected from UV-B (Collins et al., 1997)
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reported that 34 of 46 British butterfly species that might be expected to respond positively to climate warming at their northern climatic range margins in fact declined, as negative consequences of habitat loss outweighed the positive responses to climate warming over the past 30 years. Although half of the habitat generalists that also were mobile species increased their distributions, the other generalists and 89 percent of the habitat specialists declined in distribution, suggesting that the diversity of pollinators could decline substantially in the face of the combined pressures of climate change and habitat loss.
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; habitat degradation and habitat loss, in their many manifestations, have contributed to declines in many vertebrate and invertebrate pollinators.
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