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Hibiscus Sawfly

If Hibiscus leaves look like 'lace' you should suspect this pest

By: Sandy Feather ©2013
Penn State Extension


Q. My 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?

A. 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
white hibiscus

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 Hibiscus Sawfly

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.
  

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