There are two reasons why you might not use a given pesticide on a
given plant:

1) If a product hasn't been registered for use on a given plant, it
can't legally be used on that plant (Although I realize I'm the only
one who pays attention to this....). Most labels say "for yard
ornamentals:, and that can be taken to mean any plant in your yard,
including bonsai. To be on the safe side, before you spray, declare
loudly: "Why, look at these yard ornamentals!. I need to spray them as
directed by the label!".

2) If a product has been tested on a given plant species, and has been
found to be phytotoxic. When this is the case, the label will usually
say something to that effect. You should always test a product before
using it anyway, because cultivars have different sensitivites, and the
plants we use in bonsai are often not common in general ornamental
commerce.

However, my original post was cautioning against the wholesale use of
broadspectrum insecticides. This is a silly thing to do, because it
leads to development of resistant pests, and it can lead to mite
outbreaks, as well as poison the environment. Most bonsai growers
doing spot-spraying of trees with known pests are being very
responsible.

Nina.