Fly parasite not a major threat to honey beesFly parasite not a major threat to honey bees
Honey bee expert Eric Mussen said he does not consider the phorid fly as significant threat.Mussen does not see the phorids as a major threat: “All the other stresses that we have been studying have combined to impair the immune system of the bees. Then, whatever mechanism in the bees' bodies that used to prevent successful parasitism by the fly no longer is working as well. Nearly every facet we have studied--microbes, mite feeding, exposure to pesticides, etc.--all have had a suppressing effect on the honey bee immune system. The current U.S. environment seems to be very stressful to honey bees."
January 5, 2012
Noted honey bee expert Eric Mussen, Extension apiculturist with the UC Davis Department of Entomology, will discuss three decades of beekeeping when he delivers the keynote address on Thursday, Jan. 5 at the 43rd annual American Honey Producers’ Association Convention in Phoenix. Mussen will speak on “Never Expert ‘Business as Usual” in the Sheraton Crescent Hotel. He will cover pests, parasites, pesticides, diseases, malnutrition and stress.
Mussen, who joined the UC Davis Department of Entomology in 1976, will also touch on the newly announced threat to honey bees, the parasitic phorid fly (Apocephalus borealis). San Francisco State University researchers, in work published Jan. 3 in the Public Library of Science (PLoS One) journal, found that the parasitic fly lays its eggs in the honey bees; it was previously known to parasitize bumble bees, but not honey bees. (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0029639)
The infested bees reportedly fly around like zombies and cannot return to their hives.
“This information explains why some, infested, honey bee adults leave the colony at night and are not likely to come back,” Mussen said. “The percent infestation level is not high enough to cause a Colony Collapse Disorder (CCD) loss, by itself. However, anything that further stresses the bee population and increases bee losses can contribute to CCD.”
Mussen said the fly “may be contributing to the loss of adult bees from colonies, but that probably is happening, also, in colonies that are not collapsing. CCD seems to be an additive malady, so losses to fly parasitism can join the other stresses. It does not appear to be a dominant factor. ”
The San Francisco researchers detected the fly parasite in some commercial hives in California and South Dakota. Mussen said that without surveys, “we would not know for sure how widespread it is. However, it is likely that a bumble bee parasite would be distributed at least as widespread as its bumble bee hosts.”
Mussen said he does not consider the fly a significant threat. “Honey bees have an amazing ability to ‘make up for’ unanticipated losses--like exposures to bee-toxic agrichemicals in the fields--to the adult population by rearing more brood than would be expected at that time of the year to return to normal populations size. So, if the colony is shrinking, abnormally, the bees often can re-establish the normal size by rearing ‘extra’ brood. However, depending upon the inherent genetic abilities of a specific colony to tolerate fly parasitism, some colonies might be prone to developing parasite levels that are overwhelming, and actually succumb to the infestations.”
Mussen, emphasizing he does not see the phorids as a major threat, said that perhaps “all the other stresses that we have been studying have combined to impair the immune system of the bees. Then, whatever mechanism in the bees' bodies that used to prevent successful parasitism by the fly no longer is working as well. Nearly every facet we have studied--microbes, mite feeding, exposure to pesticides, etc.--all have had a suppressing effect on the honey bee immune system. The current U.S. environment seems to be very stressful to honey bees.”
Among the other speakers at the Jan. 4-8 convention will be bee breeder-geneticist Susan Cobey, who has a dual appointment at UC Davis and Washington State University. She will discuss “The Introduction of Honey Bee Germplasm and Re-Establishment of Apis Mellifera Caucasica” on Saturday, Jan. 7.
Asked about the phorids, Cobey said she learned a year ago of the San Francisco-based study. “I’m still not sure how widespread it is or how much of a problem it may be…another contributing factor in the (bee health) puzzle.”
Colony collapse disorder (CCD), first noticed in the winter of 2006, is a mysterious malady characterized by worker bees abandoning the hive. Mussen believes it is a combination of factors that suppress the immune system: pests, parasites, pesticides, diseases, malnutrition and stress.
“It’s a complex issue,” he said at a 2007 seminar at UC Davis when he chronicled bee health. “But one thing is certain: It seems unlikely that we will find a specific, new and different reason for why bees are dying.”
Hive abandonment not a new occurrence, Mussen said at the seminar. “Similar phenomena have been observed since 1869. It persisted in 1963, 1964 and 1965 and was called Spring Dwindling, Fall Collapse and Autumn Collapse. Then in 1975, it was called Disappearing Disease. But the disease wasn’t what was disappearing. The bees were.”
Although the cause of CCD is unknown, scientists have noted the high number of viruses and other pathogens, pesticides and parasites present in CCD colonies, as compared to non-CCD colonies. The high levels contribute to weakened immune systems, making the bees more susceptible to pests and pathogens.
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