Beauveria bassiana – An insect-eating fungus

Cicada or grasshopper suffering from muscardine disease
(covered by Beauveria bassiana)

I noticed something along the trail – a 1 cm, white gob hanging from the underside of a palmetto frond. It looked like a small bird dropping, except that it was alone and on the wrong side of the leaf. Something about the curvature of the spot suggested an insect. I’d read that some caterpillars and pupal cases mimic bird feces, so I pulled out my camera to take a picture.

I didn’t expect the shot to come out well. The sky was overcast and the lighting subdued, and my point-and-shoot camera struggles with objects less than an inch in length. At the same time, it couldn’t hurt to try.

In my office, I opened the pics in my editing software. Three were too blurry to be helpful, but the fourth was crisp. I zoomed on the white spot and saw that, indeed, there was an insect.

Although I’d originally believed this to be a moth pupa, the eyes were too large and suggested a cicada or grasshopper. Also, on the insect’s back I could see translucent wing tips. Were these emerging from a pupal sheath? No, because beneath the abdomen there appeared to be clear, developed wings. This had likely been a cicada or grasshopper.

The next question posed was whether the white belonged to the insect itself or was it invading? Looking at the legs, the white substance appeared to attach the insect to the leaf’s surface. Invading.

Time for a Google search: white covering insect.

No success. These weren’t whiteflies/mealybugs. I knew what those looked like.

Perhaps it was a fungus?

Next search: white fungus on insect.

Now the search narrowed. The white substance was Massospora cicadina or Beauveria bassiana. Although these fungi have similar life cycles, they affect different parts of the host. Massospora attacks the genitals and affects the mating behavior of the target insect, while Beauveria launches a generalized assault.

I looked at photos of each. With Massospora, the fungus was only visible on the lower abdomen. Beauveria covered the entire insect.

Beauveria bassiana lives worldwide in the soil. Although it can live independently, it is able to attach to plant roots and form a symbiotic relationship, through which it receives carbon and nitrogen.

It is suspected that its attacks on insects are opportunistic. Grasshoppers lay their eggs in the soil and emerging nymphs feed on low-lying plants. Hatchling cicadas drop to the earth and bury beneath the ground. Here they live most of their lives, re-emerging to become adults. As both types of insects emerge from the soil, some come into contact with Beauveria spores.

As Beauveria sits on the insect’s exoskeleton, it produces enzymes that erode the surface. Once the exoskeleton is breached, fungal hyphae (rootlike structures that allow the fungus to feed) penetrate. Fungal chemicals then weaken the host’s immune system and compete with intestinal bacteria.

The host is a rich source of carbon and nitrogen and, as a result, is consumed rapidly. Most insects die within 3-7 days, although the process may take twice as long for larger, hardier hosts such as adult beetles. Infected insects show no signs of infection while alive.

Once its food source is depleted, Beauveria bursts through the cadaver and blooms, producing more spores which fall to the ground.

Beauveria can kill most insects, but usually affects ground-dwellers. It is increasingly used as a natural pesticide in agriculture.

Although generally considered non-harmful, it has caused infections in captive reptiles. In 1979 it was found in the lungs of a dead American alligator at the Oklahoma City Zoo. In 1995 it was identified in the lungs of a dead tortoise.

In humans, four cases have been documented in immunocompromised patients. In one of these, it was found in the liver and spleen of a 38-year-old leukemia patient. Since 1984, It has also been reported in 15 cases of corneal infection associated with eye injury or contact lens use.


REFERENCES

Insecticide Update: Beauveria bassiana is safe for beneficial insects, but avoid spraying where bees forage. LSU College of Agriculture.
Beauveria bassiana. Wikipedia.
Herrington Kelly. Beauveria bassiana. Missouri University of Science and Technology, 2006.
Ortiz-Urquiza A, Keyhani N O. Molecular Genetics of Beauveria bassiana Infection of Insects (Abstract). Advances in Genetics, vol. 94:165-249. 2016 Feb 11.
Henke Markus Oliver, de Hoog G. Sybren, Gross Uwe, et al. Human Deep Tissue Infection with an Entomopathogenic Beauveria Species. Journal of Clinical Microbiology, 2002 Jul,  40(7):268-2702.
Fromtling R A, Kosanke S D, Jensen J M, Bulmer G S. Fatal Beauveria bassiana infection in a captive American alligator. J Am Vet Med Assoc, 1979 Nov 1, 175(9):934-6).
González Cabo J F, Espejo Serrano J, Bárcena Asensio M C. Mycotic pulmonary disease by Beauveria bassiana in a captive tortoise. Mycoses. Mar-Apr 1995; 38(3-4):167-9.
Ligozzi M, Maccacaro L, Passilongo M, et al. A case of Beauveria bassiana keratitis confirmed by internal transcribed spacer and LSU rDNA D1-D2 sequencing. New Microbes New Infect 2014 May; 2(3):84-87.
Atzamoglou S, Siopi M, Meletiadis J, et al. (June 17, 2021) A Corneal Perforation Related to Beauveria Bassiana and Post-Penetrating Keratoplasty Management Discussion. Cureus 13(6): e15724. doi:10.7759/cureus.15724

Published by cafsamsel

Carol Fullerton-Samsel is a nearly-native Floridian who lives with her husband of 25 years and three rescue animals. She has a passion for day-hiking and nature, and also enjoys writing. Be sure to visit the TenPaths YouTube channel, which is still in its infancy.

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