Entomopathogenic fungi

A synopsis of the abundant widespread neotropical fungi Ophiocordyceps unilateralis (likely a group of species) from Wikipedia provides an introduction to this topic:

Ophiocordyceps unilateralis is an entomopathogen, or insect-pathogenising fungus, discovered by the British naturalist Alfred Russel Wallace in 1859, and currently found predominantly in tropical forest ecosystems. O. unilateralis, also referred to as a zombie fungus, infects ants of the Camponotini tribe, with the full pathogenesis being characterized by alteration of the behavioral patterns of the infected ant. Infected hosts leave their canopy nests and foraging trails for the forest floor, an area with a temperature and humidity suitable for fungal growth; they then use their mandibles to affix themselves to a major vein on the underside of a leaf, where the host remains until its eventual death. The process leading to mortality takes 4–10 days, and includes a reproductive stage where fruiting bodies grow from the ant's head, rupturing to release the fungus's spores. O. unilateralis is in turn also susceptible to fungal infection itself, an occurrence which can limit its impact on ant populations, which has otherwise been known to devastate ant colonies.

The genus of ant infecting fungi were once all in the genus Cordyceps but most have been moved to the genus Ophiocordyceps (Sung et al. 2007).

Aegeritella superficialis
These fungi were first noted by Wisniewski in 1967 although their fungal nature was not proven then. The fungi grow over the cuticle like dark protuberances (= bulbils). On first sight, they look like dirt, and its form is usually a dome, rounded in perimeter, and up to 400 μm diameter. The number of bulbils may be from a single one to several hundred. The distribution of bulbils on the body of ants is heterogeneous, being more abundant at the rear part. The total number of bulbils is inversely related to ant size, with bigger ants having less bulbils than smaller ants. Bulbils have been detected in workers and queens.

The ant-fungus relationship has not been properly ascertained although a reduced life duration or activity level has been suggested. In a similar vein, Bałazy et al. note some workers with hundreds of bulbils, having immobilized bucal palps, all covered by hyphae. Nothing is known of the dynamics of infestation or transmission mechanisms of those enigmatic fungi, not even its phylogenetic position within the realm of Fungi.

See Espadaler & Santamaria (2012) for further details.

Aegeritella maroccana
These fungi were first noted by Wisniewski in 1967 although their fungal nature was not proven then. The fungi grow over the cuticle like dark protuberances (= bulbils). On first sight, they look like dirt, and its form is usually a dome, rounded in perimeter, and up to 400 μm diameter. The number of bulbils may be from a single one to several hundred. The distribution of bulbils on the body of ants is heterogeneous, being more abundant at the rear part. The total number of bulbils is inversely related to ant size, with bigger ants having less bulbils than smaller ants. Bulbils have been detected in workers and queens.

The ant-fungus relationship has not been properly ascertained although a reduced life duration or activity level has been suggested. In a similar vein, Bałazy et al. note some workers with hundreds of bulbils, having immobilized bucal palps, all covered by hyphae. Nothing is known of the dynamics of infestation or transmission mechanisms of those enigmatic fungi, not even its phylogenetic position within the realm of Fungi.

See Espadaler & Santamaria (2012) for further details.

Aegeritella roussillonensis
These fungi were first noted by Wisniewski in 1967 although their fungal nature was not proven then. The fungi grow over the cuticle like dark protuberances (= bulbils). On first sight, they look like dirt, and its form is usually a dome, rounded in perimeter, and up to 400 μm diameter. The number of bulbils may be from a single one to several hundred. The distribution of bulbils on the body of ants is heterogeneous, being more abundant at the rear part. The total number of bulbils is inversely related to ant size, with bigger ants having less bulbils than smaller ants. Bulbils have been detected in workers and queens.

The ant-fungus relationship has not been properly ascertained although a reduced life duration or activity level has been suggested. In a similar vein, Bałazy et al. note some workers with hundreds of bulbils, having immobilized bucal palps, all covered by hyphae. Nothing is known of the dynamics of infestation or transmission mechanisms of those enigmatic fungi, not even its phylogenetic position within the realm of Fungi.

See Espadaler & Santamaria (2012) for further details.

Aegeritella tuberculata
These fungi were first noted by Wisniewski in 1967 although their fungal nature was not proven then. The fungi grow over the cuticle like dark protuberances (= bulbils). On first sight, they look like dirt, and its form is usually a dome, rounded in perimeter, and up to 400 μm diameter. The number of bulbils may be from a single one to several hundred. The distribution of bulbils on the body of ants is heterogeneous, being more abundant at the rear part. The total number of bulbils is inversely related to ant size, with bigger ants having less bulbils than smaller ants. Bulbils have been detected in workers and queens.

The ant-fungus relationship has not been properly ascertained although a reduced life duration or activity level has been suggested. In a similar vein, Bałazy et al. note some workers with hundreds of bulbils, having immobilized bucal palps, all covered by hyphae. Nothing is known of the dynamics of infestation or transmission mechanisms of those enigmatic fungi, not even its phylogenetic position within the realm of Fungi.

See Espadaler & Santamaria (2012) for further details.

Hormiscium myrmecophilum
The species was described from an Amazonian Pseudomyrmex and remained elusive since its original description until it was found in Europe eighty years later. The filamentous, somewhat dichotomic thallus is undifferentiated and grows directly out of different parts of the ant body, without any apparent attaching structure. Mycelia have a maximum length of 163 μm and constant width of 10 μm. Spores are unknown.

See Espadaler & Santamaria (2012) for further details.

Laboulbeniales
Laboulbeniales - fungi found growing on adult ants; also associated with other arthropods

Laboulbenia camponoti
Under the binocular, the thallus of this species looks like a distorted ant hair and is found all over the body, albeit more abundant in dorsal surfaces and external surface of legs. Density is much lower than in other ant-specific Laboulbeniales. In the Holarctic, it has been detected exclusively in Camponotus species, all six from the subgenus Tanaemyrmex

See Espadaler & Santamaria (2012) for further details.

Laboulbenia formicarum
This is one of the smallest Laboulbeniales species (up to 0.3mm total length). Thalli can be extremely abundant on infested workers, which go foraging seemingly unaffected amid noninfested workers.

See Espadaler & Santamaria (2012) for further details.

Myrmicinosporidium
This fungi were first noted by Holldobler although it was formally described later, in 1933. Its phylogenetic position is still unknown, and its true fungal nature has been only proved recently. Infested ants are usually well detected because the darker spores are visible through the integument; spores number may be very low, but usually they reach more than one hundred in a single ant. The caveat here is that the fungus may be much difficult to detect in ants having fuscous or black colouration. As a consequence, host range is probably biased. The usual aspect of concave spores, with a bow-like depression, is an artefact of fixation in alcohol.

Although the infested workers are almost certainly killed by the fungus when spores begin producing hyphae, life span seems not to be curtailed. Infested workers seem scarcely affected in its normal behaviour, and infested queens may participate in swarming flights and show normal fertility. Males have been found infected too. Life cycle and mode on infestation are unknown although reports of Myrmicinosporidium from callow workers in Pogonomyrmex badius indicate that the infection is carried over from immature stages. It is perhaps significant that the majority of diseased ants were collected in late summer and fall. After hibernation, those infected workers die. Its geographical distribution is ample as is also the range of hosts.

Hosoishi et al. (2020): Myrmicinosporidium durum Hölldobler is an obligate endoparasitic fungus of ants, discovered almost a century ago (Hölldobler, 1933). The systematic position of the fungus is still unclear (Sanchez-Peña et al., 1993; Espadaler & Santamaria, 2012), but it is thought to be a member of the subphylum Entomophthoromycotina (Csata et al., 2013). The worker, queen and male castes of ants can all be infested by the fungus (Buschinger et al., 2004; García & Espadaler, 2010). It is possible to collect infested ants in pitfall traps, suggesting that the parasite does not alter the ants’ behaviour (Buschinger et al., 2004). The infested ants are easily recognized by the spores inside their bodies (Sanchez-Peña et al., 1993; Pereira, 2004), and these spores become bowl-shaped when dehydrated in alcohol (Buschinger et al., 2004). Nothing is known about the life cycle of this parasitic fungus or how it infects the host (Sanchez-Peña et al., 1993). The fungus parasites the red imported fire ants, Solenopsis invicta, but its potential use as a biological control agent is unknown (Pereira, 2004; Oi et al., 2015). We refer to the fungus as M. durum in this study, although the conspecificity of Myrmicinosporidium is uncertain due to its wide range of host species (Espadaler & Santamaria, 2012).

Rickia wasmanniii
This species is extremely characteristic in its microscopic morphological aspect and is limited to several species of Myrmica. Infested ants may harbour from a few thalli to several hundred thalli all over the body. Heavy infestations are visible to the naked eye and give a greyish shade, a pulverulent image to living individuals. Worker and queens may be infested.

See Espadaler & Santamaria (2012) for further details.

Unknown Ant Hosts
The following fungi have been reported from unknown species of ants.