Can you help me identify this caterpillar and tell me how to control
it? There are lots of them eating my baptisia, and I am afraid
it is going to die.
insect sample submitted with the question is the genista broom moth
caterpillar (Uresiphita reversalis), also known as the sophora worm
because it is a major pest of mescal bean (Sophora secundiflora) in
the Southwestern United States. It is known to exist from Nova
Scotia to Florida, west to California, and north to the Midwest.
This caterpillar has been damaging
in Western Pennsylvania this summer, including specimens in our
demonstration garden in North Park. We also received another sample
of this insect that was damaging a
golden chain tree
(Laburnum x watereri). What do these plants have in common? They all belong to
the pea family, Fabaceae. Quite honestly, this is the first time in
my professional life that I have seen anything (except deer in South
Park) damage baptisia. Apparently, there are periodic outbreaks of
this pest across the country.
Adult female moths
lay cream-colored to yellow eggs in masses on the foliage of host
plants. Newly hatched larvae construct webs and feed together until
they mature a bit, then move off and feed separately. Mature larvae
are about an inch long and are green or orange with rows of
clustered white hairs surrounded by black rings. They usually move
from their larval food plants to adjacent plants or objects where
they spin cocoons and pupate.
These caterpillars are voracious eaters and can
reduce baptisia to stems almost overnight, so they do warrant
control. Small infestations can be picked off by hand and crushed.
Larger infestations may call for the use of Bt,
sold under trade names such as Dipel or Thuricide. This naturally
occurring bacterium is specific to caterpillars, and they must
consume treated foliage for it to work, so it has no impact on other
insects. Bt only works on small caterpillars and would not provide
effective control for the mature larvae submitted by the writer.
Another option is to cut the baptisia back to a few inches, securing
the cuttings and caterpillars in a plastic bag. While it is not
ideal to cut perennials back before their time, most baptisias
should grow back with no lasting ill effects.
Many species of Genista, also
known as broom, have
been introduced to the United States as ornamental plants, and some
have become terrible weeds in certain parts of the country. In fact, genista broom moth caterpillars are considered a control
method where these plants have escaped cultivation to wreak havoc on