Chapter 46 : Made for Each Other: Ascomycete Yeasts and Insects

Many yeasts reproduce asexually by budding. Spathaspora passalidarum from a culture. Scale bar = 5 μm. Photograph courtesy of N.H. Nguyen.

The edge of a 9-cm plate showing discrete budding yeast colonies developed on agar after streaking. Photograph courtesy of S.-O. Suh.

Hat-shaped ascospores of Scheffersomyces stipitis. Ascospore shape was once thought to be a good phylogenetic character in yeasts. DNA sequencing indicates it has arisen independently several times, not only in yeasts, but also in Pezizomycotina. Scale bar = 5 μm. Photograph courtesy of S.-O. Suh.

Odontotaneus disjunctus (Passalidae). (A) Partially dissected beetle shows the gut and its regions in situ. (MG, midgut; PHG, posterior hindgut; AHG, anterior hindgut. (B) Foregut (FG), MG, AHG, and PHG removed from the beetle. A surface film of attached bacteria is located in the differentiated AHG; Sheffersomyces stipitis is attached in the PHG (see Fig. 10 ) ( 78 ). Preparation and photograph courtesy of N.H. Nguyen.

Xylosandrus amputatus (Curculionidae: Scolytinae: Xyleborini). Large, complex bilobed mesonotal mycangium (stained blue) with opening on the pronotum; spores of the mycangial symbiont Ambrosiella nakashimae at the edge of the pronotum. Fungi in Ceratocystidaceae, including A. nakashimae, have close associations with certain species of beetle and produce arthrospore-like cells rather than yeast-like budding typical of other ambrosial symbionts. Photograph courtesy of Chase G. Mayers.

Pselaphacus nigropunctatus, a species of beetle (Erotylidae) with parental care; red speckled adult beside a late instar larva (grub) on white basidiocarp of a wood-decaying fungus in Bolivia. Photograph courtesy of J.V. McHugh.

The name of the yeast genus Suhomyces recognizes Dr. Sung-Oui Suh for his studies of yeasts in the field and laboratory. Barro Colorado Island, Panama, July 2002. Photograph, M. Blackwell.

Four yeast biologists (l. to r. Drs. Marc-André Lachance, Clete Kurtzman, Jack Fell, and Teun Boekhout) at a coffee break at a meeting to celebrate the centenary of the CBS-KNAW Fungal Biodiversity Centre (since February 10, 2017, known as the Westerdijk Fungal Biology Centre), Utrecht, The Netherlands, in Amsterdam, April 2004. The genus Teunomyces recognizes the research of Dr. Boekhout; all the others also have yeast genera named for them and are cited in this chapter. Photograph M. Blackwell.

Ascoidea asiatica (NRRL Y-17632), an ambrosia fungus disseminated by insect vectors, was isolated from a beetle larva in wood. This species has been reported to be associated with lymexylid ship timber beetles. Asci with hat-shaped ascospores developed on agar, although budding cells and abundant hyphae are also produced under the cultural conditions. Hat-shaped ascospores are a convergent character (see Fig. 3 ). Scale bar = 10 μm. See reference 133 . Photograph courtesy of Cletus Kurtzman.

Water mount made without a cover slip of the interior hindgut of Odontotaenius disjunctus (Passalidae) showing several thalli attached along a furrow in the hindgut. Scale bar = 100 μm. See reference 77 .

Brown planthopper, Nilaparvata lugens, feeding on a rice stem. The insect and YLS harbored in its fat body are obligately associated for essential nutritional resources. Photograph courtesy of Sylvia Villareal, International Rice Research Institute.

Yeasts are usually studied from isolations made in petri dishes, and their life histories in nature are largely unknown. The yeast described as Ascobotryozyma americana (CBS 8560) and the nematode Panagrellus dubius have a unique phoretic relationship with the poplar borer beetle (Coleoptera, Cerambycidae, Saperda calcarata) that would be unobserved in pure culture. The yeast uses its bifurcate basal cell as a holdfast to attach to the nematode, and they both fly away on a beetle to get to a fresh environment. Scanning electron micrograph, bar = 0.4 mm. See reference 120 . Courtesy of J. Kerrigan.

Ascospores of Pyxidiophora sp. photographed 24 h after being placed on agar. No cover slip was used, so it looks a little foggy. The ascospore produced several conidia at the ascospore tip, and these budded several times more to produce yeast cells before hyphae elongate. The yeasts are likely dispersed over the new substrate by the mite, improving the chance of finding a suitable fungal host in this complex life history. Scale bar = 50 μm. M. Blackwell.