"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift
Showing posts with label bee. Show all posts
Showing posts with label bee. Show all posts

August 9, 2013

Ascosphaera apis

This is the second post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2013. This particular post was written by Karen McDonald on a paper published in 2008 on how bees use resin to protect their hive against fungal parasites (you can read the previous post about toxic birds and their lice here).

Animals have evolved many different strategies to fight parasite infections; from eating tough or poisonous leaves (which would normally never be chosen as part of their diet), dirt bathing, grooming themselves with plants that contain chemicals that kill parasites, living in hostile environments that parasites can't tolerate, to drinking toxic substances like alcohol to kill internal parasites. Animals in general are individuals and care only for their own personal well-being and so the parasite-ridding strategies animals use really only affect their own health and well-being. But bees, on the other hand, are different.

SEM photo of Ascosphaera apis sporeball from here
Bees are communal animals and each bee is an important part of the hive community. The article I am going to talk about today shows that bees don't act on a self-motivated level where they are only concerned with their own well-being, instead bees work only to improve and support the whole hive community. Wild bees always smother the inside of their nests with sticky plant resin and the reason for this was never really understood. Domesticated bees don't use much, if any resin at all. They have been selectively bred to not use it because the sticky resin makes opening the hive and removing the honey and combs very difficult. But domestic bees are also plagued by many, often destructive, parasites.

In 2008 researchers decided to document whether the amount of plant resin that domestic bees use in their hives has an effect on fungal parasite levels in that hive. Two groups of hives were set up; the first group of 12 had the inside of each box painted with thick resin to replicate the nests of wild bees, the second group of 11 boxes were only painted with the type and quantity of resin used by commercial apiaries. Bees from both groups were fed with pollen infected with Chalkbrood, which they ate and/or carried back to their hives.

Photo of chalkbrood-infect larvae from here
Chalkbrood (Ascosphaera apis) is a fungal infection of bee larvae, causing them to die and mummify in the nest (see photo on the right). Adult bees are not affected by the parasite but they do carry it in their bodies and drop spores throughout the nest infecting young bees. Normally, as mentioned above, infected animals are usually only concerned with their own well-being and so the researchers were interested in seeing whether the adults would react to the threat to the larvae or ignore the parasite menace because it did not affect them personally.

Within days, the bees immediately began collecting more resin for their nests. Normally, there are only a few bees in each hive that forage for resin, the majority forage for pollen or nectar. Bees do not eat resin; its only function is to line the nest, so not much energy is used by the hive community to collect it. But when the hive is under threat from a parasite like Chalkbrood, more bees begin to forage for resin and a lot of energy is used to find it.  The nests painted with resin, although infected at the same level, also had a reduced level of infection compared to the commercial standard nests, but the level of infection in all nests dropped as the amount of resin in the nest increased. The bees were using the resin as a form of  social immunity rather than self-immunity.

Simone-Finstrom M.D., Spivak M., (2012) Increased Resin Collection after Parasite Challenge: A Case of Self-Medication in Honey Bees? PloS One, 7(3): e34601. Doi: 10.1371/journal.pone.0034601

This post was written by Karen McDonald

January 3, 2012

Apocephalus borealis

Many of you have heard of the very scary phenomenon called "Colony Collapse Disorder" - and if you haven't, you should, because it could be a major threat to the food we eat. CCD is when the worker honey bees abandon their hives and die, which, if widespread, can mean drastic decreases in pollination of crops. This phenomenon was first reported in the U.S. in 2006 and ever since that time, scientists have struggled to uncover what was responsible. Everything from cell phone radiation to genetically modified crops to a variety of parasites of honey bees were suggested to be the cause. Then, today, a new paper in PLoS One showed data suggesting that another kind of parasite is linked to CCD. Apocephalus borealis is a parasitoid fly that was known to attack bumblebees and paper wasps, but now has been demonstrated to also attack honeybees in the U.S. - in fact, 77% of the colonies sampled near San Francisco were parasitized by A. borealis. The authors used DNA barcoding to confirm that the flies in the honey bees were genetically indistinguishable from those parasitizing bumble bees.

The authors of the new study also found that bees that were found flying around at night (something honey bees don't normally do) were significantly more likely to be parasitized by the fly and furthermore, the sick bees also seemed disoriented. It is not currently known whether or not the tendency for the parasitized bees to fly at night away from their colonies is another example of manipulation of the host by a parasite or whether this might be an act of altruism by the bee, carrying its parasite away from its colony and thus protecting the others.

Although these new results are very exciting, many questions remain to be answered about the history and impact of A. borealis. First, when did the switch into honey bees occur? Honey bees are not native to the U.S., but since they are so well monitored and studied, the authors believe that the switch must have happened recently - otherwise it would have been noticed by apiculturists. Second, could these flies also be serving as vectors for other bee pathogens? Two known bee pathogens, Deformed Wing Virus and Nosema ceranae, a microsporidian were found in the A. borealis flies. And finally, could the invasion of honey bees by this parasite mean that CCD is going to increase? The natural hosts of A. borealis are bumble bees, which live in small colonies where only the queen herself survives the winter, but honey bee colonies have thousands of bees and their activity maintains some amount of heat, even in colder winter months. This increase in host resources and more generations per year could spell a population explosion of A. borealis...and that won't be good for those of us who depend on pollination - like all of us.

The image is from the paper. Look closely at the abdomen of the bee - that's a little parasitic fly laying eggs into it. Soon the larvae will emerge from the dead host. (You can see a photo of this in the original paper as well.)

Source: Core A, Runckel C, Ivers J, Quock C, Siapno T, et al. (2012) A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis. PLoS ONE 7(1): e29639. doi:10.1371/journal.pone.0029639.

November 9, 2010

November 9 - Meloe franciscanus

Today's parasite is the larval stage of the blister beetle Meloe franciscanus. The beetle larvae are brood parasites that feed on eggs and the young of the solitary bee Habropoda pallida. The problem is, how do they get into the nest of a female bee on the first place? Well they do it by imitating the real thing. They gather into a swarm and climb to the tip of a grass stem. Once there, they clump together to form a small brown blob. While it might not look like much to you, but beetles give off a smell and produce vibrations that fool a male bee into thinking that the blob is one fine hottie. For the beetle larvae, it's a collective effort - the more of them there are in the blob, the more attractive they appear to a male bee. As soon as the bee comes into range expecting to get lucky, all the beetle larvae jump onboard. The experience leaves the bee slightly shaken, but unstirred, and he continue on his quest to find a female bee. However, once he does find a real female, he also ends up passing on his sticky hitch-hikers as a sexually transmitted infection. Once the beetles are all onboard the poor female, they cling on for dear life, eventually disembarking at her nest where they will be surrounded by all the food they'll ever need to grow up.

Photo credit: SFSU

Contributed by Tommy Leung.

February 8, 2010

February 8 - Coelioxys coturnix

A female Coelioxys (Allocoelioxys) coturnix Pérez bee dashes into the nest of another bee species, Megachile minutissima Radoszkowski, and lays an egg on top of her host’s. She has waited—loitering outside the nest while assessing the whereabouts of the other female —for the other’s moment of weakness: leaving the nest to collect the last bit of material to close the brood chamber containing her egg and the pollen and nectar provisions for the larva that will emerge from the egg. Coelioxys coturnix is a cleptoparasitic (sometimes spelled “kleptoparasitic”) bee, an entomological version of the cuckoo bird, that does not collect food or nesting material for her offspring but uses the nests and, in bees, larval provisions of other species. Depending on the species of parasitic bee, its newly hatched larva might have disproportionately large, fang-like jaws to kill the host’s brood, might feed on the host’s egg, or might (in one very unusual species from Florida currently being described) wait until it is almost too late, during its last larval stage, to do away with the competition. Cleptoparasitism has evolved many times among bees using different pathways, according to Jerry Rozen, a Curator at the American Museum of Natural History for nearly 50 years, who has studied these bee species for much of his career.

Contributed by Kristin Phillips.
Photography by Rollin Coville.

January 10, 2010

January 10 - Varroa destructor

Many people have heard of grave concerns about the loss of honey bees, key pollinators of our crops and other important plants. One of the reasons for their trouble is the ectoparasitic mite, Varroa destructor. These tiny little arachnids climb onto bees and suck out their hemolymph - insect blood - and can also transmit dangerous viruses from bee to bee.