Synergism of aflatoxin Bl toxicity with the co-occurring fungal metabolite kojic acid to two caterpillars

Kojic acid is a secondary fungal metabolite that is commonly produced by many species of Aspergillus and Penicillium (Manabe et al., 1984). These fungi also produce mycotoxins that occur as components of distinctive secondary metabolite profiles, which can serve as reliable chemotaxonomic characters at the species level (Dorner, 1983; Frisvad & Filtenborg, 1983; Wicklow, 1984a). The mycotoxin aflatoxin Bl> which is produced by Aspergillus jlavus Link: Fr., is highly toxic (LD50 0f7.2 mg/kg to rats), mutagenic, and carcinogenic (Cole & Cox, 1981). However, kojic acid, which is also produced by A. f!avus, is relatively nontoxic (LD50 of 1765 mg/kg to mice (Cole & Cox, 1981), and has not been implicated in any naturally occurring toxicoses to man or animals (Wilson, 1981). In fact, kojic acid is produced by most of the strains of the domesticated kojic mold, A. oryzae (Ahlburg) Cohn [=Aspergillusjlavus var. oryzae (Kurtzman et al., 1987)] that are used in the preparation of Oriental fermented foods (Murakami, 1971). Mycotoxins are considered to be of adaptive significance in the defense of fungal thalli from predation (Wicklow & Cole, 1982), or in preventing mammals or birds from consuming seeds infected by the fungi (Janzen, 1977). Invertebrates (i.e. insects) are a likely target for these mycotoxins, since they consume a variety of products that are also infested by mycotoxin-producing fungi (Wicklow, 1984b). For example, A. f!avus may colonize the developing maize kernels that may also be fed on by the fall armyworm [Spodopterajrugiperda (1. E. Smith)] and the corn earworm [Heliothis zea (Boddie)] (Fortnum, 1985). In higher plants, chemicals that are of low toxicity and co-occur with plant toxins may act as synergists of these toxins (e.g. myristicin and xanthotoxin), although actual demonstration of this phenomenon has been limited (Berenbaum, 1985). Co-occurring mycotoxins may also cause additive or synergistic toxicity to mammals (Ciegler, 1972). Kojic acid has been reported as a synergist of the plant toxin nicotine (Mayer et al., 1946). However, its native or ecological role when produced by A. jlavus may be to act as a synergist of the co-occuring aflatoxins. This research investigates the toxicity of aflatoxin B1 and kojic acid, alone and in combination, to S. jrugiperda and H. zea.