Diversity, prevalence and virulence of fungal entomopathogens in colonies of the ant Formica selysi

Abstract

The richness of the parasitic community associated with social insect colonies has rarely been investigated. Moreover, understanding how hosts and pathogens interact in nature is important to interpret results from laboratory experiments. Here, we assessed the diversity, prevalence and virulence of fungal entomopathogens present around and within colonies of the ant Formica selysi. We detected eight fungal species known to be entomopathogenic in soil sampled from the habitat of ants. Six of these entomopathogens were found in active nests, abandoned nests, and corpses from dump piles or live ants. A systematic search for the presence of three generalist fungal entomopathogens in ant colonies revealed a large variation in their prevalence. The most common of the three pathogens, Paecilomyces lilacinus, was detected in 44% of the colonies. Beauveria bassiana occurred in 17% of the colonies, often in association with P. lilacinus, whereas we did not detect Metarhizium brunneum (formerly M. anisopliae) in active colonies. The three fungal species caused significant mortality to experimentally challenged ants, but varied in their degree of virulence. There was a high level of genetic diversity within B. bassiana isolates, which delineated three genetic strains that also differed significantly in their virulence. Overall, our study indicates that the ants encounter a diversity of fungal entomopathogens in their natural habitat. Moreover, some generalist pathogens vary greatly in their virulence and prevalence in ant colonies, which calls for further studies on the specificity of the interactions between the ant hosts and their fungal pathogens.

Microfungi associated with a myrmecophyte Macaranga bancana

“…This is consistent with previous studies that examined microfungi associated with nests of ants (Reber and Chapuisat 2012), nests and fungus gardens of leafcutting ants (Fisher et al 1996;Rodriguez et al 2008Rodriguez et al , 2011Carlos et al 2011), and ant bodies Guedes et al 2012). These previous studies consistently reported the occurrence of species of Fusarium and its teleomorphic states (Gibberella and Nectria), Aspergillus,Paecilomyces,and Penicillium (cf.…”

“…(Reber and Chapuisat 2012), were not isolated from M. bancana. Paecilomyces lilacinus, a close relative of OTU7, has been shown to be pathogenic to ants ) and humans (Luangsa-ard et al 2011).…”

Effects of the social environment on the survival and fungal resistance of ant brood

“…Workers from singlequeen (=monogyne) colonies are also significantly larger than workers from multiple-queen (=polygyne) colonies (Schwander et al 2005) and have a slightly higher activity in one component of the immune system causing bacterial growth inhibition, even when controlling for body size (Castella et al 2010). Surprisingly, F. selysi workers originating from polygyne colonies showed a lower survival rate than workers from monogyne colonies when they were experimentally challenged with an entomopathogenic fungus, despite the fact that experimental groups with higher diversity had higher resistance (Reber et al 2008). This result suggests that, while diversity per se improves the resistance of the group, some other aspect of the polygyne lifestyle reduces the ability of workers to resist infections.…”

“…Little is known about how the worker/brood ratio affects other aspects of offspring quality, such as maturation time and resistance to infection. Recent studies of parasite resistance in social insects indicate that gene by environment interactions are probably important in worker susceptibility (e.g., Reber et al 2008). Both genetic and environmental factors are known to affect disease resistance in other organisms, including birds (e.g., Saino et al 1997;Soler et al 2003), mammals (e.g., Lubach et al 1995;Prager et al 2010), and insects (e.g., Cotter et al 2004;Moreno-Garcia et al 2010).…”

Foster carers influence brood pathogen resistance in ants

“…The B. bassiana strain that we used was originally collected from our field site [25; strain B2], and this concentration has caused an intermediate mortality rate in past experiments [25,32,33]. We randomly assigned the first cross-fostered worker emerging from each rearing group to either the B. bassiana challenge or control; thereafter, we alternated the treatment applied to each subsequent cross-fostered worker from the same rearing group.…”