Species-specific responses of dew fly larvae to mycotoxins

Abstract

The larval stages of saprophagous insects and filamentous fungi have been demonstrated to be serious competitors on decaying organic matter. When filamentous fungi appear to be competitively superior, fungal mycotoxins have frequently been suggested to constitute chemical weapons, causing high mortality among insect larvae. In this study, we tested whether typical fungal secondary compounds can indeed be considered as the underlying mechanism of interference competition between filamentous fungi and various saprophagous Drosophila species. In contrast to our expectation, we found no grand mycotoxin-specific effects, but insect survival appeared to be generally determined by complex interaction between toxin identity, toxin concentration and insect species. Three out of five drosophilids seemed to be equally affected by the mycotoxins used in this study, whereas two species showed toxin-specific changes in survival. Only two (Kojic acid and Ochratoxin A) out of seven mycotoxins caused insect-specific responses. Moreover, we discovered correlations between survival in toxin-free and spoiled substrates, which may indicate an interrelationship between intra-specific competitive ability and resistance to mycotoxins. We discuss the significance of mycotoxins as underlying mechanisms driving competitive insect-fungus interactions.

Effect of Fungal Colonization of Wheat Grains with Fusarium spp. on Food Choice, Weight Gain and Mortality of Meal Beetle Larvae (Tenebrio molitor)

“…Moreover, producing diverse volatile components fungi could easily gain fitness benefits by attracting, repelling or remaining invisible to potential insect hosts, competitors or vectors depending on selective pressures. Indeed, recent studies revealed the role of fungal toxins in interactions of fungi with fungivorous arthropods [49]–[52]. Enhanced production of fungal toxins as a defense response of Aspergillus nidulans against fungivorous collembolans was recently established [53].…”

Fungal secondary metabolites as modulators of interactions with insects and other arthropods

“…In addition to a possible role of some secondary metabolites in fending off competing microbes, secretion of insecticidal mycotoxins, such as aflatoxin B 1 (Chinnici and Bettinger, 1984;Rohlfs and Obmann, 2009), by a well-coordinated vesicle transport machinery (Chanda et al, 2009) may create an adverse environment in decaying fruits, dung, carrion and the like (Hodge and Mitchell, 1997;Rohlfs et al, 2005;Trienens et al, 2010) that harms insects exploiting the same resource patch. Similar to the phenomenon of allelopathy among plants, the export of toxic secondary metabolites might drive competition between insects and fungi.…”

Fungal metabolic plasticity and sexual development mediate induced resistance to arthropod fungivory

“…In species of the wide-spread fungal genus Aspergillus, highly toxic polyketides are prime candidate compounds for direct chemical defence against generalist fungivores, as ingestion of these mycotoxins causes dose-dependent impairment of arthropod fitness [11]. Knocking out genetically the mechanisms that control the regulation of cytotoxic and carcinogenic sterigmatocystin (ST) and other secondary metabolites in the mould Aspergillus nidulans [12] leads to a striking preference of fungivorous collembolans, Folsomia candida, for the chemicaldeficient mutant strain [13].…”