The spore producing apparatus in Beauveria is small and delicate. It is very difficult to make a good slide mount to show the fine details of origin and development (= ontogeny) of the spores. You will not find many (= any?) good pictures on the web of spore production in Beauveria. The photomicrograph above shows three conidiogenous cells (= spore mother cells) on a hypha (= fungal filament) of Beauveria bassiana. The conidia (= asexual spores) ) are produced in acropetal succession (= youngest at the tip) on an elongating conidiogenous cell (= cell that produces conidia). Conidium is the name given to the non sexual spore that germinates by means of a germ tube that is produced in the Hyphomycetes (= class) of the Deuteromycota (= Division for asexual fungi).
Sympodial Spore Production in Beauveria
In B. bassiana the spores are produced sympodially. A spore is produced at the tip of the mother cell and the growth of the mother cell ceases. A new growing point initiates just below this terminal spore, grows past it, and a second spore is produced at a higher level. This uses up the new growing point and a third growing point is then initiated just below the second spore. Every time a spore is produced the hyphal tip is used up and a new growing point is produced. In this way a succession of spores is produced with the youngest spore at the tip (= i.e acropetal succession) and the spore head gets longer and longer. When all the spores secede (= are dislodged) the spore-bearing tip of the conidiogenous cell has a zig zag appearance and is referred to as a rachis ( this term is also used for the seed head in wheat when all the seeds are gone).
Biology of Beauveria
Beauveria bassiana is an aggressive parasite of many different insect host species. Not only does it have a wide host range but insects are attacked at larval or adult stages. The spores are tiny, measuring only a few microns. The hyphae and spores are non pigmented (hyaline) and so colonies appear white in cultures or tufts of white mycelium bearing masses of powdery spores burst out through the body parts of infected insects as in the cicada, hawkmoth and chinch bugs illustrated below (click on thumbnail). For something really dramatic look at the synnematal form of Beauveria I found growing on a hawkmoth. And right next to that is a couple of hairy chinch bugs that I recovered from the chinch bug population inhabiting my lawn.
Beauveria bassiana: Cicada (left); HawkMoth Larva (centre) and Chinch Bug (right).
1. How did I make the micrograph above of Beauveria without dislodging the conidia from their very delicate attachments to the conidiogenous cells?
2. Biocontrol of Insects diseases of Plants. A formulation of Beauveria is sold commercially to control a number of pest insects. One formultion kills all or does it? Because of the biocontrol aspects with the commercial release of bioinsecticides using Beauveria, there is now a host of papers on the web dealing with this aspect of Beauveria. Check some of these out?
3. A study in Holland showed that Beauveria spores were strongly allergenic. How does this influence recommendation for control of insects in greenhouse conditions or in field conditions?
4. Alternaria is also a common cause of allergies. The spores of Beauveria are only 2-3 X 2 microns long and the spores of Alternaria alternata (a common species) are 20-60 by 10-20 microns. Has this any significance in the induction of allergies, or in the allergic response, or in any recommendations based on counts per cubic metre ( the usual way of estimating bioaerosols).
5. I have a chinch bug infestation every year that wipes out large sections of my lawn. I have decided that I should use my knowledge of Beauveria to control this problem without using pesticides. You are my number one assistant. Outline how you would solve my problem.
6. If Beauveria bassiana has an extremely wide host range then what is the significance of 'non target' effects? Has anyone done a critical study on this? How would you carry out a study to address this problem? What about strain selection to tackle a specific host insect?
7. How do Chinch bugs survive the winter in the North Temperate zones?
PESTICE BAN: Use of pesticides has been banned in Guelph, Ontario as of 2009. What do I do now to control Chinch Bug. The ill informed city hall council will allow the use of pesticides when symptoms of Chinch Bug are manifested. Unfortunately by that time the damage is done for that year and spraying in July or August will do little to reduce the damage for that year. For chinch bug you have to spray during the intermediate (instar) stages of the insect's growth (little red dots!) when they are most susceptible and the least damage has been done to the grass. For the alert student, early warning of the presence of chinch bugs is tillering of the grass (proliferation of very fine grass blades) in heavily infested areas.