Close-up of a varroa mite on a drone pupa. (Photo by Kathy Keatley Garvey)

When the American Beekeeping Federation (ABF) meets Jan. 9-13 at the Grand Sierra Resort, Reno, Nev. for its 75th annual American Beekeeping Federation Conference & Tradeshow, the key concern is bee health.

Sadly, colony losses continue to take their toll.

Our nation's honey bee colonies are down slightly for operations with five or more colonies, according to statistics released Aug. 1, 2017 by the U.S. Department of Agriculture (USDA).

In its news release, the USDA's National Agricultural Statistics Service noted that "Honey bee colonies for operations with five or more colonies in the United States on January 1, 2017 totaled 2.62 million colonies, down slightly from January 1, 2016. The number of colonies in the United States on April 1, 2017 was 2.89 million colonies. During 2016, honey bee colonies on January 1, April 1, July 1, and October 1 were 2.62 million, 2.80 million, 3.18 million, and 3.03 million colonies, respectively."

Honey bee colony loss (for operations with five or more colonies) amounted to 362,000 colonies or 14 percent. "The number of colonies lost during the quarter of April through June 2017 was 226,000 colonies, or 8 percent," according to the USDA news release. "During the quarter of October through December 2016, colonies lost totaled 502,000  colonies, or 17 percent, the highest of any quarter in 2016. The quarter in 2016 with the lowest number of colonies lost was April through June, with 330,000  colonies lost, or 12 percent."

And again, no surprise: the No. 1 colony stressor was that dreaded varroa mite (Varroa destructor) and the viruses it can transmit. The parasitic mites suck the blood (hemolymph) from both the adults and developing brood, especially drone pupae.

The ABF conference will zero in on the varroa mite at several presentations on Thursday, Jan. 10:

• "Selecting for Behavioral Resistance to Varroa Destructor"--Krispn Given, Apiculture Specialist, Purdue University Department of Entomology, West Lafayette, Ind.
• "RNA Viruses and Varroa Mites: Temporal Variation in Honey Bee Pathogens Influences Patterns of Co-Infection"--Alex Burham, University of Vermont, Burllngton, Va.
• "Engaging Beekeepers with MiteCheck: Implementing a Nationwide Citizen Science Program for Monitoring and Comparing Varroa destructor Infestations"--Rebecca Masterman, University of Minnesota, St. Paul, Minn.

Overall, the diamond-anniversary conference will focus on educational sessions, social and networking activities "and lots of opportunities to learn about new products and services," according to ABF president Gene Brandi of Los Banos, a bee industry leader for four decades. He currently manages some 2000 colonies in central California with his son.

Morris Weaver of Montgomery, Texas, the 1975-76 ABF president, will deliver the keynote presentation on "The American Beekeeping Federation, Inc.: 75 Years Strong."

Attendees can choose from five track sessions: small scale beekeepers; serious sideliners; package bee and queen breeders; honey producers and packers; and commercial beekeepers. Registration also will take place at the door.

On Saturday, Jan. 13, Amina Harris, director of the UC Davis Honey and Pollination Center, will present two honey-tasting workshops: "Taste and Evaluate Honey: Matching Flowers to Flavors."

This week is truly a gathering of bee scientists and beekeepers. In conjunction with the ABF conference, the American Bee Research Conference will take place Jan. 11-12 in Reno.  Marla Spivak, MacArthur Fellow and Distinguished McKnight University Professor, University of Minnesota, is the keynote speaker.

Varroa mite on a honey bee (drone) pupa. (Photo by Kathy Keatley Garvey)

We remember seeing a varroa mite attached to a foraging honey bee one warm summer day in our pollinator garden. The mite was feeding off the bee and the bee was feeding on the nectar of a lavender blossom.

Didn't seem fair.

We've never seen a varroa mite on bumble bees or carpenter bees, but Davis photographer Allan Jones has--and he's photographed them. (See below)

When varroa mites tumble off a honey bee and into a blossom, they can hitch a ride on other insects, such as bumble bees and carpenter bees.

"Varroa have been recorded hitching rides on bumble bees and yellowjackets," observed native pollinator specialist Robbin Thorp, distinguished emeritus professor of entomology at UC Davis. "Varroa have been reported as feeding on larvae of these and other critters--but not successfully reproducing on them.  Also bumble bees and yellowjackets typically overwinter as hibernating queens not as perennial colonies like honey bees.  Thus they are not suitable hosts for Varroa."

Extension apiculturist emeritus Eric Mussen says that bees other than honey bees aren't reproductive hosts for the varroa mite.

"As far as I know, Varroa destructor may be able to find soft areas of the exoskeleton of insects other than honey bees and feed on them," he says. "I have no idea whether or not the substitute hemolymph would sustain the mites for very long.  The mites have practically no digestive capabilities.  They simply utilize the previously-synthesized bee blood, to which they seem to be perfectly adapted."

 "Since the mites reproduce on honey bee pupae, there are a number of considerations about potential other reproductive hosts," Mussen said, citing:

1.  Are the nutrients of the substitute host close enough to those of honey bees to support immature mite development? 
2. Can immature mites that develop properly at honey bee cell environmental conditions (temperature and relative humidity) find a similar environment in the nests of other insects? 
3. Do other insects tolerate the presence of mites on their bodies or in their brood nests?

Like honey bees, bumble bees do segregate their pupae in single cells, Mussen says, but he was unable to find any studies devoted to whether bumble bee pupal conditions support Varroa destructor reproduction.

Sounds like a good research project!

Newly published research by a Michigan State University-led team indicates that one of the reasons why the varroa mite is so destructive is because it infiltrates hives by smelling like a bee.

The parasitic mite, or Varroa destructor, is a "blood sucker" that feeds on bees. Scientists and beekeepers alike consider it the world's No. 1 enemy of honey bees.

MSU entomologist Zachary Huang,  a lead author of the paper in Biology Letters, and his fellow researchers showed that "mites are able to change their surface chemicals to an entirely different species of honeybees," according to an article in the American Bee Journal. "Further, they also revealed that the mites were able to make these changes rather quickly - adapting in days rather than evolving over generations."

The varroa mite was initially found in Asian honey bees (Apis cerana) and then shifted hosts to the European honey bee (Apis mellifera). It was first detected in the United States in 1987. Today it is found in hives throughout the world except in Australia.

The eight-legged reddish-brown parasite, about 1–1.8 mm long and 1.5–2 mm wide, is a blood sucker that's difficult to control, according to Extension apiculturist emeritus Eric Mussen of the UC Davis Department of Entomology and Nematology. Mites transmit viruses (there are now some 22 named RNA viruses) that can wipe out a hive. A familiar mite-transmitted disease that beekeepers see is DWV or Deformed Wing Virus. Mites can also lower the protein level of a bee's blood, and reduce its weight and life span.

Mussen says that mites spread from colony to colony by phoresy (animal-to-animal transport). They ride on flying drones (males) and adult worker bees (females). They also spread changing hosts on flowers.

"A mite enters a honey bee cell just before or during the time it is being capped," Mussen points out. "It feeds on older larva or prepupa. Sixty hours later, the mite lays its first egg. The egg will hatch in about 24 hours."

"The number and release of offspring depend on the length of the pupal stage. The queen is pupa for 8.5 days (no mites). The worker is pupa for 12.5 days (1.3 mites) and the drone is pupa for 14.7 days (3 or 4 mites)," he says. Thus, due to the longer time required for drone development, drone pupae get the worst of it.

"When maturing, the newly emerged mites climb onto adult bees and feed by puncturing the intersegmental membranes and sucking the bee blood," Mussen related recently to a UC Davis class. "Often these are nurse bees that stay around the brood nest. Sometimes the hosts are drones and older foragers that are flying from the hive every day. Eventually the new mite climbs off the nurse bee onto a comb in the brood nest and enters a cell. The reproductive cycle starts and within 6 days, 44 percent of the young mites have moved into the brood cells; within 12 days, 69 percent of the mites are in the brood cells; and within 24 days, 90 percent of the mite are in the brood cells."

"If there is no brood, the mite has to feed on adult bee blood every six days or so to remain alive," Mussen says. "Mite life expectancy in summer is around 60 days; bees about 42 days. Mite life expectancy in the winter is up to 9 months; bees about six months."

Now if scientists could only figure out how to eliminate the varroa mite from the world's hives...

Varroa mite on a drone pupa. (Photo by Kathy Keatley Garvey)

And it's an enemy to be reckoned with, Extension apiculturist Eric Mussen told students in the UC Davis "Biology of Parasitism" class, taught by forensic entomologist Robert Kimsey and nematologist Steve Nadler, Department of Entomology and Nematology.

Guest-lecturing at a special session held at the Harry H. Laidlaw Jr. Honey Bee Research Facility, UC Davis, Mussen talked about the varroa mite--its history, biology, damage and control methods--and then opened several hives at the apiary.

The Varroa destructor, a native of Asia, is now found in hives throughout the world except in Australia. It was first detected in the United States in 1987.

The eight-legged reddish-brown parasite, about 1–1.8 mm long and 1.5–2 mm wide, is a blood sucker that's difficult to control, Mussen said. Mites transmit viruses (there are now some 22 named RNA viruses) that can wipe out a hive. A familiar mite-transmitted disease that beekeepers see is DWV or Deformed Wing Virus. Mites are also known lowering the protein level of a bee's blood, and reducing its weight and life span.

Mussen said that mites spread from colony to colony by phoresy (animal-to-animal transport). They ride on flying drones (males) and adult worker bees (females). They also spread changing hosts on flowers.

"A mite enters a honey bee cell just before or during the time it is being capped," Mussen said. "It feeds on older larva or prepupa. Sixty hours later, the mite lays its first egg. The egg will hatch in about 24 hours."

"The number and release of offspring depend on the length of the pupal stage. The queen is pupa for 8.5 days (no mites). The worker is pupa for 12.5 days (1.3 mites) and the drone is pupa for 14.7 days (3 or 4 mites)," he said. Thus, due to the longer time required for drone development, drone pupae get the worst of it.

"When maturing, the newly emerged mites climb onto adult bees and feed by puncturing the intersegmental membranes and sucking the bee blood," Mussen related. "Often these are nurse bees that stay around the brood nest. Sometimes the hosts are drones and older foragers that are flying from the hive every day. Eventually the new mite climbs off the nurse bee onto a comb in the brood nest and enters a cell. The reproductive cycle starts and within 6 days, 44 percent of the young mites have moved into the brood cells; within 12 days, 69 percent of the mites are in the brood cells; and within 24 days, 90 percent of the mite are in the brood cells."

"If there is no brood, the mite has to feed on adult bee blood every six days or so to remain alive," Mussen said. "Mite life expectancy in summer is around 60 days; bees about 42 days. Mite life expectancy in the winter is up to 9 months; bees about six months."

Mussen also discussed how to detect mite infestations through non-chemical and chemical methods,  and listed chemical treatments being used throughout the nation. Mites are developing resistance to a few chemical treatments, he pointed out. And, some of the chemical treatments not only kill the mites, but damage or kill the queen and the brood.

Beekeepers who try to go organic, figuring that "if the bees can't make it on their own--if they're not fit--let them die" are really doing a disservice to neighboring beekeepers, Mussen said. The mite will overrun a colony and then  infest other colonies.

Public Enemy No. 1--definitely a force to be reckoned with.