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A fly known to parasitize American bumble bees and wasps has recently been discovered parasitizing California honey bees, causing bees to abandon their colonies in the night. The investigators, who published a report this week in PLOS 1, think that the parasite's jump to honey bee hosts happened recently. Commercial transport of potentially infected bees to new areas needs to be stopped immediately to prevent the global spread of this serious threat to food production and the environment.

Bees parasitized by the phorid fly became disoriented, "turning into zombies", flying out into the night to die the next day. Parasitism was widespread in the study area near the San Francisco Bay. Parasitism was found at 77% of the sites they investigated. The highest rate of parasitism was 91% of the nocturnally active bees at one site.

Parasitism was associated with high rates of viral infection in the bees studied. Because the virus was also found in the flies, the scientists suspect that the parasitic flies are vectors for bee diseases. Colony collapse disorder continues to be considered caused by multiple factors, but the phorid flies may involved in several factors.

Healthy vs Unhealthy colonies hat tip to Wee Mama for image source
We found widespread parasitism by A. borealis amongst 7,417 honey bees and 195 bumble bees (177 Bombus vosnesenskii, 18 Bombus melanopygus) sampled from San Francisco Bay Area localities. In all, 77% of our sample sites (24 of 31) yielded honey bees parasitized by A. borealis.
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While there are previous reports of night activity in honey bees, we are the first to link night activity to hive abandonment. We first found stranded worker honey bees beneath lights and within light fixtures on the campus of San Francisco State University under a variety of weather conditions including cold rainy nights when virtually no other insects were seen around lights. Stranded bees showed symptoms such as disorientation (walking in circles) and loss of equilibrium (unable to stand on legs). Unlike most insects attracted to light, stranded bees remained mostly inactive the next day until they died. Honey bees that left their hives at night had a much higher rate of parasitism by A. borealis than bees foraging during the daytime (χ2 = 133, d.f. 1, p<0.0001) (Figure 3A). From October 2009 to January 2010 parasitism rates were as high as 91% in one sample of nocturnally active bees with a mean parasitism rate of 63% for that period (SD = 18.5, Range = 32%–91%, n = 266 bees) (Figure 3A).


The scientists sternly warn the public of the severe risks posed by the parasitic flies.

The host shift from bumble bees to honey bees has potentially major implications for the population dynamics of A. borealis. Bumble bees live in relatively small colonies that last only a single season with only queens overwintering. Honey bees, on the other hand, live in much larger colonies with tens of thousands of individuals living in hives that are warm even in winter. If these flies have or can gain the ability to reproduce within hives they could greatly increase their population size and levels of virulence. Moreover, hundreds and sometimes thousands of commercial honey bee colonies are often found in close proximity to one another in agricultural areas. Such high host density might lead to population explosions of the fly and major impacts on the hives they parasitize. Further, A. borealis is already widely distributed across North America [14] (Figure 1).
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Apocephalus borealis may also be a threat to native pollinators since it parasitizes a number of bumble bee species and paper wasps (Vespula spp) [13], [14]. Wild bumble bees are experiencing substantial declines in North America [44], [45]. So far, attention has focused on emerging pathogens such as Crithidia bombi and Nosema bombi. In the laboratory, bumble bees parasitized by A. borealis show a dramatic reduction in life span compared to unparasitized bees [13]. The high rate of parasitism in some of our samples of foraging bumble bees and previous high parasitism rates from Canada [13], suggest that parasitism by A. borealis, especially in combination with infection by emerging pathogens, could place significant stress on bumble bee populations. If so, phorid parasitism or pathogen transmission to bumble bees might contribute to a cascade of effects in plant and agricultural communities that rely on bumble bees as pollinators. Furthermore, the domestic honey bee is potentially A. borealis' ticket to global invasion. Establishment of A. borealis on other continents, where its lineage does not occur, where host bees are particularly naïve, and where further host shifts could take place, could have negative implications for worldwide agriculture and for biodiversity of non-North American wasps and bees.


Apparently, commercial transport of bees has already spread the parasites to multiple states in the United States.

Distribution of phorid-infected honey bees sampled in this study (red).

Inset shows the San Francisco Bay Area counties where we found phorid-parasitized honey bees. The routes of commercial hives tested are indicated (arrows), where dotted lines represent states the hives crossed before viral microarray testing and solid lines represent the route of hives during the period of microarray testing. Sites where A. borealis was previously known [7] are indicated by black dots.

Although catastrophic losses of honey bee colonies have occurred in the past, the magnitude and speed of recent hive losses appear unprecedented [1]. So far, the main causal suspects have been parasitic mites, fungal parasites, viral diseases and interactions amongst them [1]–[5]. While viral and microsporidian infections have been linked to increased mortality and declining health in honey bee colonies [5], [6], studies have not directly addressed behavioral changes involved in abandonment of hives.

Honey bees suffer from numerous parasites and pathogens including viruses, bacteria, parasitic fungi and ectoparasitic mites [7]. Infections from agents within any of these pathogen and parasite groups can be fatal to honey bees, but the parasitic Varroa destructor mite appears to be the most harmful to colonies overall. Varroa destructor is widespread in honey bee hives, affecting every life stage of honey bees from larva to adult [8]. Probably because of this, beekeepers in the United States rank parasites as a bigger threat to their honey bee colonies than CCD [1]. Controlling for parasitic mites is time consuming and costly with damage control estimated in the billions of dollars worldwide [9]. Further, V. destructor has been implicated as a vector of many pathogens that can compromise colony health [10]–[12]. Understanding parasitic infections in honey bees is crucial in predicting the long-term health of honey bee hives.

Images of Apocephalus borealis and honey bees.

(A) Adult female A. borealis. (B) Female A. borealis ovipositing into the abdomen of a worker honey bee. (C) Two final instar larvae of A. borealis exiting a honey bee worker at the junction of the head and thorax (red arrows).

Here we report that Apocephalus borealis, a phorid fly native to North America, previously known to parasitize bumble bees and paper wasps [13], [14], also attacks the non-native honey bee. The genus Apocephalus is best known for the “decapitating flies” that parasitize a variety of ant species [15]. Apocephalus borealis belongs to the subgenus Mesophora, which is a group that contains species that attack hosts other than ants. Although the hosts of most species in the Mesophora group are unknown, previously discovered hosts include a variety of arthropods including bees, wasps, beetles and spiders, but not honey bees [14].

Previous DailyKos Posts on Bee CCD

US Bumble bee Population Implodes, Drops 96%

Bee Catastrophe Threatens American Crop Failure

The Great Bee Swarm of 2010

Bee Colony Collapse Mystery Clues Revealed

Found: a cause of Colony Collapse Disorder UPDATE-5

This is the most important underreported story

Originally posted to DK GreenRoots on Thu Jan 05, 2012 at 10:31 AM PST.

Also republished by SciTech and Backyard Science.

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