Mycangia of ambrosia beetles

Ambrosia beetles evolved a variety of morphological structures to carry their fungal symbionts from tree to tree. These structures are generally called mycangia. A nice classification of mycangia was published by Diana Six (Six, 2003). The main difference between different kinds of mycangia is whether or not they are external or internal, and whether they secrete substances relevant to the fungus containment or not.

In case of nonglandular mycangia on the surface, it is not clear that they actually serve that purpose. In cases where no mycangium has been found, spores or conidia of ambrosia fungi may be carried in the beetle’s digestive system (Biedermann, unpubl.)

Some people use the term “mycetangia”, but this often refers to a cluster of cells within an organ that house mutualistic endocytobionts inside the body cavity (Ganter, 2006). This is mostly called mycetocyte. More commonly it houses symbiotic bacteria, and then it is more properly called “bacteriocyte”.

Our lab has experimented with 3D imaging of the mycangia in certain beetles. Watch video and read about our techniques in Entomology Today.

Fig: Surface pit mycangia. Left: Female of Treptolatypus solidus with glandular pit mycangia on top of the pronotum (Photo J.H.). Right: Simple nonglandular pit mycangium on the head of Scolytodes unipunctatus. Arrow on the right points to a fungus spore. (photo M. Kolarik).

Fig: Invaginated mycangia. Left: Mandibular mycangia inside the frontal part of head of Xyleborus affinis filled with fungal spores. Photo J.H. & K. Miller. Right: Large invaginated sac mycangium in Xylosandrus germanus. These have intense secretion activity, and are often stuffed full with fungal spores. Photo J.H.

References

Ganter, P.F. (2006). Biodiversity and Ecophysiology of Yeasts. In The Yeast Handbook, pp. 303-370. Springer, Berlin Heidelberg.

Six, D.L. (2003). Bark beetle-fungus symbioses. In: Insect Symbiosis. Bourtzis, K. and Miller, T. A., eds. CRC Press, New York, pp. 97-114.