Detecting subtle effects of diet preservatives on European corn borer (Lepidoptera: Crambidae)

A wheat germ-casien-agar diet for rearing European corn borer, Ostrinia nubilalis Hübner, contains five preservatives, sorbic acid (0.055% w/w), para-hydroxybenzoic acid methyl ester (methyl paraben, 0.144% w/w), propionic acid (0.488% w/w), aureomycin (0.292% w/w), and phosphoric acid (0.084% w/w). We conducted studies to determine if the first four of these preservatives can be reduced. In the first experiment we eliminated simultaneously propionic acid and aureomycin and either retained all sorbic acid and methyl paraben or reduced them by 50% or eliminated them as well. The diet with full sorbic acid and methyl paraben and no propionic acid and aureomycin performed similar to the unchanged control. All other diets resulted in microbial contamination that reduced survival of larvae. In the second experiment, we compared 5 diets, the full complement of sorbic acid and methyl paraben with elimination or 50% reduction of both propionic acid and aureomycin, elimination of aureomycin and 50% reduction in propionic acid. The last diet had no aureomycin or propionic acid and 50% reduction in methyl paraben. Some of the replicate dishes with diets without any propionic acid or aureomycin had microbial contamination that reduced survival of larvae. Larval survival was similar for the remaining diets. The diet without aureomycin and 50% reduction in propionic acid produced large larvae that were about half as variable in size as those from the control diet, suggesting that a reduction in these preservatives would increase moth uniformity. No differences in development rate were observed among the diets.