Saprophagous insect larvae, Drosophila melanogaster, profit from increased species richness in beneficial microbes

To make food resources accessible, provide supplemental nutrition and fend off parasites, animals, including humans, often rely on symbiotic microorganisms (Dethlefsen et al. 2007; Rosenberg et al. 2007; Klepzig et al. 2009). In contrast, many microbes, such as filamentous fungi or bacteria, render food sources unpalatable to animals (Janzen 1977; Burkepile et al. 2006; Rozen et al. 2008). Insects often face diverse antagonistic interactions with filamentous fungi, this could be one reason why they may have been selected for establishing associations with specific bacteria or yeasts that impair fungal growth, possibly on grounds of their capacity to synthesize anti-fungal metabolites (Kaltenpoth et al. 2005; Cardoza et al. 2006; Little et al. 2006; Scott et al. 2008; Haeder et al. 2009; Lam et al. 2009; Rodrigues et al. 2009). Drosophilid flies are a prime example of the large group of saprophagous insects whose larvae develop on dead organic material, e.g. rotting plant tissue (Shorrocks 1982), that is concomitantly inhabited by various microorganisms. For a successful development the fly larvae depend on the availability of dietary yeasts (Begon 1982; Anagnostou et al. 2009) that may be transferred to the breeding site by adult flies (Wertheim et al. 2002; Rohlfs and Hoffmeister 2005), suggesting a mutualistic Drosophila–yeast relationship (Vega and Dowd 2005). Nevertheless, the immature insects may also encounter noxious microbes, e.g. mould fungi that can cause high mortality among the animals (Rohlfs et al. 2005). Recent pharmacological tests indicate that the interference