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Status of Pollinators in North America
the wings (Akratanakul and Burgett, 1975), and reduced longevity (DeJong and DeJong, 1983).
Varroa parasitism of A. mellifera drones also can affect the ability of the queen to obtain adequate supplies of healthy sperm during mating. Parasitism has been associated with reduced sperm quality (Collins and Pettis, 2001) and with decreases in adult weight, size of seminal vesicles, and mucus. Effects of parasitism on male behavior include a decline in the frequency of flight (Schneider, 1986) and decreased flight performance, sperm production, and mating efficiency (Bubalo et al., 2005; Duay et al., 2002).
Varroa parasitism of honey bees is associated with viral pathogens, and some damage attributed to varroa mites is actually viral in origin (Allen and Ball, 1996). Although some viral diseases of honey bees are associated with varroa infestations (Kevan et al., 2006; Oldroyd and Wongsiri, 2006), which negative effects are exclusively attributable to direct actions of the mites or to their associated pathogens is unknown (Chen et al., 2005). “Parasitic mite syndrome” is used to describe colonies that exhibit a constellation of symptoms, including the presence of diseased adult and immature bees, adults with deformed wings, and crawling bees at hive entrances (Shimanuki et al., 1994). Once this syndrome is apparent, the colony begins a rapid decline in adult worker population and viable replacement brood. It dies, typically within 3–6 weeks of the onset of symptoms.
The rate at which the varroa mite population increases in a honey bee colony depends in part on the rate at which individual mites reproduce (Fries et al., 1994). Some stocks of honey bees, such as neotropical Africanized honey bees (see section on Invasive Species in this chapter), are less susceptible to varroa mites than are other stocks, apparently because they have slightly faster developmental times, thus depriving the mites of the time necessary for successful reproduction (Camazine, 1986).
Twenty years after its introduction to the United States, V. destructor continues to devastate honey bee populations. High losses have been reported locally (Burgett, 1994; Loper, 1995) and nationally. During the winter of 1995–1996, northern U.S. beekeepers experienced their largest losses in history; in some states, 30 to 80 percent of colonies were lost (Finley et al., 1996). Similar losses were observed in the winters of 2000–2001 and 2004–2005 (Caron and Hubner, 2001; Lumkin, 2005). Data on colony losses are derived from informal surveys of beekeepers, and the exact causes of colony deaths have not been established. 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). These honey bee losses have occurred despite the industry’s heavy reliance on pesticides to control mite populations. Pesticide resistance has become widespread (Elzen et al., 1998, 1999d) and many beekeepers are no longer able to use the few registered pesticides for varroa control.