Tuesday, 19 March 2013

Beauveria bassiana - A Fungus That Kills Bed Bugs

Beauveria bassiana is a fungus that is well known for killing insects. Spores of B. bassiana adhere to the cuticle (the outer protective covering) of the insect, begin to grow, and work their way through to the inner tissues. There the fungal growth continues, taking nutrients from the host's body until the insect dies. Because B. bassiana is lethal to many insects, including their larvae, it has been grown and distributed commercially for use in agricultural control of insect pests. It makes sense to wonder whether it could be used to control bed bugs as well.
Beauveria bassiana is grown for control of agricultural
pest insects. Image courtesy of Keith Weller.

Beauveria bassiana Kills Bed Bugs


A study by Alexis Barbarin et al tested B. bassiana against bed bugs, and the results indicate that the fungus is lethal to the pests: not only does it kill virtually all bugs that come in contact with it, infected bugs can carry it back to daytime hiding places and pass it on to other bugs that have not been otherwise exposed. Barbarin el al propose that B. bassiana might rid a bed bug infested building of its bugs.

Bed Bug Traps Using Beauveria bassiana


In their study, Barbarin et al exposed bed bugs to a mixture of oil and fungal spores on various surfaces, and found that jersey knit cotton transmitted the infection most effectively. Though further research is required, they propose that a fabric bed skirt impregnated with B. bassiana spores might be an efficient means of infecting a resident bedbug population. Presumably any trap designed so that all bedbugs climbing onto or leaving the bed would have to pass through it could be used to infect them with the fungus.

Is Beauveria bassiana Safe for Humans?


Beauveria bassiana is generally regarded as safe for humans and it's already being used for insect control applications all over the world without dire consequences for human health. This fungus is already naturally occurring in the environment. However, there's reason to be cautious with this approach. A study that tested fungi isolated from poultry barns found that B. bassiana has several virulence factors that potentially “increase [its] survival, growth, and propagation... in animal tissue.” Authors Taira el al comment, quite correctly, that otherwise harmless fungi can cause serious infections in people whose immune systems are already compromised. Such people include AIDS patients and organ donor recipients among others.

These grasshoppers were killed by Beauveria bassiana.
Fungal growth is visible on the insects' remains.
Image courtesy of Stefan Jaronski.

Cases of both deep tissue infection and skin infection caused by B. bassiana have been reported in the medical literature (Figueira et al). The possibility of skin infection, in particular, prompts second thoughts. Beauvaria bassiana does not wipe out bed bugs on contact: it takes time for the infection to kill. Therefore, bugs that have contacted the fungus will still visit the sleeping host to feed. And while feeding, they will create a break in the skin, often with severe irritation resulting, and possibly introduce fungal spores. This does not seem like a good plan.

Beyond the possibility of skin infection arising from contact with the bugs, a spore impregnated bed skirt would presumably contaminate a living space with fungal spores pretty thoroughly, and fungal spores are as hardy and as hard to eliminate as bed bugs are. Under the right conditions, they could remain viable for a very long time, possibly protecting against reinfestation by bed bugs, but also a potential hazard for the immunocompromised occupant of, or visitor to, the space.

Sources


Barbarin AM, Jenkins NE et al. “A Preliminary Evaluation of the Potential of Beauveria bassiana for Bed Bug Control.” Journal of Invertebrate Pathology 111 (2012) 82–85

Figueira L, Pinheiro D et al. “Beauveria bassiana Keratitis in Bullous Keratopathy: Antifungal Sensitivity Testing and Management.” European Journal of Ophthalmology 22:5 (2012) 814-818

Taira CL, Marcondes NR et al. “Virulence Potential of Filamentous Fungi Isolated From Poultry Barns in Cascavel, ParanĂ¡, Brazil.” Brazilian Journal of Pharmaceutical Sciences 47:1 Jan./Mar. 2011



No comments:

Post a Comment