leaves look like 'lace' you should suspect this pest
By: Sandy Feather
children gave me two hardy hibiscus shrubs for my birthday. They
have been doing well and blooming gloriously, but now something
seems to be eating the leaves. I just noticed the damage, but some
of the leaves look like lace. I checked for bugs, but I do not see
anything. Do you have any suggestions?
It sounds as though the hibiscus sawfly has found your new plants.
Your description of the damage fits with the damage created by this
small, caterpillar-like insect. It can cause similar damage on
hollyhocks and possibly other members of the cotton family. Although
it can be called the hibiscus sawfly or the hollyhock sawfly, this
particular insect has no generally accepted common name among
entomologists. Its Latin name is Atomacera decepta.
The larva, or immature insect, is the damaging stage of this pest.
It is spiny and green, about 3/8-inch long, with a black head. The
hibiscus sawfly is easy to overlook since it is about the same shade
of green as the leaves. It resembles a caterpillar, but that term is
reserved for the larvae of moths and butterflies. One way to tell
the difference between sawfly larvae and caterpillars is count the
fleshy, abdominal prolegs. Sawfly larvae will have six or more pairs
of abdominal prolegs while caterpillars have five or fewer.
White Hibiscus flower
Hibiscus sawfly is one of the most important pests to
affect hibiscus plants, but it has not been studied extensively.
There are several generations of this pest every year, right up
until frost. Adults lay their eggs on the undersides of the leaves,
generally toward the tip. The adults are small (less than 1/4-inch),
fly-like insects that are black with an orange thorax. The larvae
hatch and begin feeding, and turn hibiscus and hollyhock leaves into
lace. They pupate in debris around the base of the plant, and then
hatch out as adults, and the whole life cycle begins anew.
Insecticide Controls for
Insecticide sprays are very effective in controlling
this pest, but you have to scout your hibiscus plants frequently for
the damage and the larvae that cause it. Rotenone and pyrethrins,
Captain Jack’s Deadbug Brew (spinosad), Sevin (carbaryl) and Bayer
Advanced Garden Multi-Insect Killer (cyfluthrin) should provide
adequate control. Begin making applications when you first notice
damage and find the larvae feeding on the leaves. You will need to
make repeated applications to control subsequent generations.
How to prune