By Savannah Richard

Not much attention is given to non-agricultural related insect pathogens and parasitic fungi, making these fungi all the more mysterious and fascinating. Ophiocordyceps unilateralis is a fungal pathogen that parasitizes its host; in this case Camponotus leonardi ants and other close relatives are the victims. Ophiocordyceps unilateralis is in the Ascomycota phylum and was previously in the Cordyceps family but has recently diverged into its own genus (Pontopiddan et al 2009). This fungus can be found in most tropical environments from South America, Africa to Eastern Asia.

Ants become infected when they are on the forest floor foraging and spores, laying on leaves or other dead ants, attach to the exoskeleton. These spores penetrate the ant’s exoskeleton to eat away at the soft tissue inside. During this process of feeding off the ants tissue the fungus produces compounds that affect the ant’s brain and subsequently change the ant’s behavior. The exact cause is still unknown but the infected ants crawl up a tree and attach themselves using their mandibles to the underside of a leaf. Mycelia then grow through the bottom exoskeleton of the ant onto the leaf to help secure the ant (Anderson et al 2012). Ants have also been found to position themselves facing north almost exactly 25cm from the forest floor; in high humidity areas. These conditions are ideal for fungal growth and are attributed to the fungal pathogens control of the ant’s behavior, hence the nickname zombie fungi (Andersen et al 2009).

After the ant has attached itself to the leaf and has died, the fungus begins the last part of its life cycle. A wiry stalk grows out of the ant’s head that has perithecia (spore bearing surface) at the ends, as shown in this video: http://www.youtube.com/watch?v=XuKjBIBBAL8. The fungus then drops the spores back onto the forest floor and waits for another host to pass through to infect. The entire life cycle of Ophiocordyceps unilateralis takes around 4-10 days. This fungus is also known to attack large groups of ants and almost wipe out entire colonies (Anderson et al 2009). This leaves behind several ant corpses on the underneath of leaves which scientists have coined as “ant graveyards”. Ants have adapted ways of sensing graveyards and avoiding these areas in the forest. With this developed sensitivity to Ophiocordyceps unilateralis ants have also been shown to carry out other infected ants into the forest away from the rest of the colony (Pontoppidan et al 2009).

All Cordyceps species including Ophiocordyceps species are thought to have medicinal properties. Cordyceps species produce a bio-metabolite called cordycepin, which has anti-inflammatory and anti-tumor properties. Cordyceps also contain many nutritional compounds such as B1, B2, B12, and K vitamins. In traditional Chinese medicine Cordyceps were used to aide in bronchitis, asthma, respiratory and cardiovascular diseases. Pharmaceutical companies have been able to isolate cordycepin and turn it into powder form for mass production. Culturing Cordyceps is now being experimented with to some degree of success and may expand in availability sometime in the near future (Tuli and Sandhu 2013).

References:

Andersen, S., Ferrari, M., Evans, H., Elliot, S., Boomsma, J., Hughes D., (May 2012)

Disease Dynamics in a Specialized Parasite of Ant Societies. Plos One. Retrieved from: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0036352

Andersen, S., Gerritsma, S., Yusah, K., Mayntz, D., Hywel-Jones, N., Billen, J., Boomsma, J., Hughes, D. (September 2009) The Life of a Dead Ant: The Expression of an Adaptive Extended Phenotype. The American Naturalist, Volume 174, No.3 Retrieved from http://www.jstor.org/stable/10.1086/603640

BBC Worldwide. Cordyceps: attack of the killer fungi- Planet Earth Attenborough BBC wildlife. ( November 2008) Retrieved from: http://www.youtube.com/watch?v=XuKjBIBBAL8.

Pontoppidan, M., Himaman, W., Hywel-Jones, N.,  Boomsma, J., Hughes, D., (March 2009) Graveyards on the Move: The Spatio-Temporal Distribution of Dead Ophiocordyceps-Infected Ants. Plos One. Retrieved from: http://www.plosone.org/

Tuli, H., Sandhu, S., (February 2006) Pharmacological and Therapeutic potential of Cordyceps, with special reference to cordycepin. 3 Biotech, volume 4, issue . Retrieved from: http://link.springer.com/article/10.1007/s13205-013-0121-9

By Kaitlyn Texley

We’ve all heard it said, without bees humanity would cease to exist four years after. Thanks to a fungus we may be approaching this apocalyptic prediction. Colony collapse is nothing new. We’ve read about it, seen it on TV and heard conspiracy theories about the multitudes of causes. Recent research into what is actually causing the rapid collapse revealed that it is actually the parasitic microsporidia Nosema ceranae.  Even weirder, bees exposed to fungicides and pesticides the rates of fungal infection, or nosemosis, are even higher (Pettis, et al 2013).

The spores of the N. Ceranae enter through the bee’s mouth and travel into the mid-gut. In bees, the mid-gut is where the digestive enzymes used to break down pollen reside. Here the microsporidia’s spores grow, reproduce and create more spores. The microsporidia feeds off of the cells within the bee’s mid gut causing damage and weakening the bee. As it does this, the microsporidia also inhibits the genes responsible for the regeneration of the intestinal tissue (Dussaubat et al, 2012). So not only is the mid gut being digested and consumed by the fungi, the bee’s body can’t heal any of the destruction.

The bee’s body responds by generating antioxidant enzymes and sending them to the site of the Nosema ceranae infection (Dussaubat et al, 2012).  This seems to do little for the poor bee. The microsporidia continues to ravage the intestinal tract eventually travelling to the rectum and out with the bee’s poop. Healthy worker bees then clean up the poop and become infected by the microsporidia themselves.

The effects are really terrible. The little worker bee can have 30-50 million spores within their tiny little body (Nosema ceranae and nosema disease of honeybees, 2010). Of course this has an impact on their well-being. They become tired and are unable to produce “brood food” because of the total takeover by the fungus. This food is meant to be eaten by the baby bees, however in a severe case of Nosema ceranae infection, there may not be many babies. If the queen becomes infected her ovaries stop working and she is unable to produce eggs, and thus, babies (Nosema ceranae and nosema disease of honeybees, 2010).

How does a hive get exposed to the microsporidia? Sometimes honey-bees will rob other hives if they can’t get enough food. If they rob a hive that has honey containing Nosema ceranae spores they’re screwed (Nosema ceranae and nosema disease of honeybees, 2010). Apiaries can also increase the likelihood of infection by combining two dwindling colonies, both of which are, unbeknownst to the apiary, infested with Nosema ceranae (Nosema ceranae and nosema disease of honeybees, 2010).

Figure 1.  Nosema ceranae life cycle.

The severity of the colony’s infection coincides with the seasons.  During the colder spring months when the weather is sporadic, the bees are stuck inside of their hives. This is also when baby making begins, the worker bees are continually cleaning out contaminated combs for new baby bees and being exposed to the microsporidia. This is when the hive become highly infested and usually, if the infection is bad enough, when the colony itself collapses. If the colony does not collapse and they make it to summer, they are offered a new chance. The drones and worker bees (the adults affected by the fungus) leave the hive and die. The baby bees emerge microsporidia-free and the combs of the hive are cleaner as brooding has decreased. It’s a new lease on the colony’s life.

If the coming fall is wet, good conditions for microsporidia, the bees have a higher chance of contracting Nosema ceranae again. If the fall is dry, the colony may be safe from the infection for the following year.

It’s important for farmers, apiaries and scientists to learn as much as possible about Nosema ceranae so they can prevent the contraction of it. Although not all fungus are bad, Nosema ceranae is dependent on the bee’s mid-gut to reproduce and thrive. Unfortunately this is not only bad news for the little honey bee that’s infected, it’s bad news for the entire colony, and in fact the entire human population. If colonies keep collapsing, we may not only have a shortage of honey, we may have a shortage of nearly 1/3 of the planet’s food supply (Yang, 2006). That is not a small amount. In fact, that is a very large amount. You would have to say goodbye to blueberries, almonds and many other fruits, vegetables and nuts.

So although you may not care very much about Nosema ceranae and what it’s doing to a bee’s mid-gut, you will care when the repercussions of this widespread infection effect the food choices at your local grocery store. With a reduction of pesticides and fungicides the susceptibility for an infection to happen and spread will decrease (Pettis, et al, 2013). Along with knowledge of how the microsporidia spreads farmers, apiaries and scientists may be able to reduce the spread of Nosema ceranae and keep our food where it belongs, on our plates!

References:

Moisset, Beatriz, Buchmann, Stephen. Bee Basics; An Introduction to Our Native Bees. (2011). Retrieved January 28, 2014, from http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5306468.pdf

Dussaubat, Claudia et al. Gut Pathology and Responses to the Microsporidium Nosema ceranae in the Honey Bee Apis mellifera. (2012). PLOSone. DOI: 10.1371/journal.pone0037017

Pettis, J., Lichtenberg,E., Andree, M., Stitzinger, J., Rose, R., vanEnglesdorp, D. (2013). Crop Pollination Exposes Honey Pees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae. PLOSone. DOI: 10.1371/journal.pone.0070182

Nosema ceranae and nosema disease of honeybees. (2010). Retrieved January 26, 2014, from http://www.biosecurity.govt.nz/pests/nosema-ceranae.

Yang, Sarah. Pollinators Help One-Third of World’s Crop Production, Says New Study. (2006) UC Berkeley News. Retrieved January 28, 2014, from http://berkeley.edu/news/media/releases/2006/10/25_pollinator.shtml

Photo: http://scientificbeekeeping.com/the-nosema-twins-part-1/