I have never heard of a problem with Best Press and insects. I understood it to be any plant based starch. Here is info from Orkin's website about silverfish: "They are especially attracted to paper and damp clothing. Commonly found in stored boxes in garages and sheds.
Silverfish feed on carbohydrates, particularly sugars and starches. Cellulose, shampoos, glue in books, linen, silk and dead insects may be food sources. Have been found in unopened food packages."