Effects of yeast on the growth and reproduction of the saprophagous millipedePolydesmus angustus (Diplopoda, Polydesmidae)

The millipedePolydesmus angustus was reared in the laboratory from hatching to maturity, reproduction and death. Two food types were used: dead leaves alone or dead leaves supplemented monthly with dry food yeast (Saccharomyces cerevisiae) at a rate not exceeding 5% of leaf dry weight. Growth, survival, adult live weight and fertility were compared between females reared on the two diets. Although the species was able to complete its life cycle on dead leaves alone, several parameters were strongly affected by the addition of yeast: growth was significantly faster, adult females became significantly larger and there was a 4.3-fold increase in fertility. Only survival was unaltered by the addition of yeast. The comparison between these laboratory results and field data on female fertility and live weight suggests that the natural diet of millipedes includes foods of higher quality than dead leaves. Possible sources of high-quality food in natural conditions are discussed.