23 October 2013

A versatile fungus

This blog post was written by postgraduate student Jenny Brookes as part of the course, Research Methods in Ecology (Ecol608). Jenny revisits a Lincoln University research area that look at using fungus to kill insect pests published in 2011.

Writing a blog has proved more difficult than I remembered. Having a done previous blog in 2011 entitled jennysinsectcorner, I recall it as being easier than this one!!! Or perhaps memories fade. The brief for this blog was to base it on a research paper written by a staff member or student of Lincoln University at the time of publication. The paper I chose was ‘Persistence of Beauveria bassiana (Ascomycota:Hypocreales) as an endophyte following inoculation of radiata pine seed and seedlings’ which was written by four authors, including Professor Travis Glare of Lincoln University. Reading the paper has re-enforced my view of how incredible fungi can be.
The fungal genus Beauveria has numerous species (Beauveria bassiana,1 of which I will talk about here) that are simultaneously;
1. An endophyte, a fungi within a plant, helping the plant in a specific way,
2. An entomopathogenic fungus (that is a fungus within a plant that is a pathogen to an insect but not affecting the plant.)
3. Able to not just deter but to kill insects.

 Photo 1.  Beauveria bassiana with the distinct identification formation  of ‘cotton balls’. Photo by Jenny Brookes

Beauveria bassiana (photo 1) can be endophytic in several plant species. The idea is to inoculate a target plant, for example pines trees (photo 2,) and then when the trees are attacked by insects, the fungus will kill or deter those insects. Two Beauveria bassiana isolates (F647 and F668) were found in mature wild pine trees (Pinus radiata) and were used to inoculate pine tree seedlings by two methods-Seed coating and root dipping.

Photo 2.  Beauveria bassiana isolated from within a pine needle. Photo by Jenny Brookes
This raises more interesting questions of how a fungus can kill an insect. Infection occurs when conidia (the spores) land on the insect and germinate. The spore grows a germ tube and a special blob called an appressorium (Diagram 3) which penetrates the insect cuticle at the junction of plates in the insect's exoskeleton called sclerites.

 Diagram 3; Courtesy of APSnet illustrating the infection process in a plant. The germ tube grows into the appressorium then penetrates the cells. This is in a plant but the same principle works in insects penetrating the haemocoel or insect blood system.

The fungus invades deeper into the insect and eventually causes death. This is the trigger for Beauveria to make spores (sporulate) and protrudes outside the insect to release spores to continue its life cycle. The poor unfortunate  insect is eaten from within; a long and slow death (photo.4).
It could be considered a cruel and barbaric death. The fungi steals the ‘goodies’ out of the haemocoel and spreads slowly through the insect avoiding organs that will kill the insect prematurely. Even after the insects death it will continue to spread until there is nothing left and then it will protrude outside and sporulate. If this happened to us , this could be considered torture or worse. We see in photo 4 a weta which has been killed by a natural infection of Beauveria bassiana found in the wild and given to Professor T. Glare by a colleague.

 Photo 4.  A natural infection of Beauveria bassiana protruding from the cuticle of a weta (Orthoptera).Photo by Jenny Brookes

The insect killing skills of Beauveria are now being put to good use in bio-controls worldwide. It was used by USA to control fire ants. Cornell University did a study with grasshoppers and found that at lower temperatures, mortality of the grasshoppers increased.
Regardless of how cruel the insect world may be our society prefers to have natural solutions to man-made problems. Just two of many Beauveria-based commercial products developed so far are called Beaublast and Beaugenic made by a company in the North Island, New Zealand. I believe we will see more natural products especially fungal based, what do you think? Would you hire fungal killers to kill your insect pests?

Links to more sites for Beauveria bassiana you may want to explore.

Integrated Pest Management. http://www.hort.uconn.edu/ipm/general/htms/bassiana.htm
Beauveria bassiana  http://www.uoguelph.ca/~gbarron/MISCELLANEOUS/nov01.htm
Know your friends. The entompopathogen Beauveria bassiana. http://www.entomology.wisc.edu/mbcn/kyf410.html


Brownbridge M., Reay S.D. Nelson T.L. Glare T.R. (2012); Persistence of Beauveria bassiana (Ascomycota:Hypocreales) as an endophyte following inoculation of radiate pine seed and seedlings. Journal of Biological Control 61:194-200. http://www.sciencedirect.com/science/article/pii/S1049964412000102

American Phytopathological Society (APS)APSnet; Glossary accessed 29/4/2013; https://www.apsnet.org/edcenter/illglossary/Article%20Images/germtube.JPG

No comments: