Thanks for your question.  It would really be helpful if I could have two pictures.  One showing a skeletonized leaf, and a second picture of the fly.

Many thanks.



Thanks for the pictures.

Although the resolution is not great on the pictures, I believe this is an adult Hibiscus Sawfly (Atomacera decepta). It is an invasive species that was first reported in the Midwest around 2011. Because of its rather recent appearance, information is still being gathered with respect to its life history. Hibiscus and hollyhocks are closely related plants belonging to the same plant family (Malvaceae). It’s not surprising therefore, that this insect pest found its way to your hollyhocks. The larvae are the culprits who did the number on your hollyhocks. They feed on the underside of the foliage, leaving a lacy appearance to the leaves that is seen in your first picture.

See the following (note that it shows a larva feeding on a hollyhock leaf; note how carefully it is eating around the leaf veins):

https://bugguide.net/node/view/310011/15740

What you are now observing are the adult sawflies. They do virtually no damage to hollyhocks, but they do lay eggs. These adults should be eliminated. See (note that it shows an adult on a hollyhock):

https://bugguide.net/node/view/795315

See the following for further information including remedial procedures:

https://content.ces.ncsu.edu/hibiscus-sawfly - :~:text=The caterpillars of Atomacera decepta,lacy network of leaf veins.

https://content.ces.ncsu.edu/hibiscus-sawfly

https://extension.umd.edu/resource/sawflies/

https://bugoftheweek.com/blog/2021/9/27/mallow-munchers-mallow-sawfly-aka-hibiscus-sawfly-atomacera-decepta

https://arthropod.uark.edu/mallow-or-hibiscus-sawfly/

If you cut you hollyhocks back this fall, clean up all plant debris and discard in the trash. Do not compost it. This debris will contain eggs of this sawfly. I wonder if the damage done in 2024 was by this sawfly and not Japanese beetles? Good luck. Please get back to us if you have any further, related questions.

Thanks for getting back to us regarding insecticides against the hibiscus sawfly. Here are some possibilities:

1). Spinosad: very effective against sawfly larvae; examples of products: Monterey Garden Insect Spray, Captain Jack’s Deadbug Brew; targets insect nervous systems.

2). Pyrethrins: Fast-acting contact insecticide; examples of products: PyGanic, Safer Brand Insect Killing Soap with Pyrethrin; contact kill.

3). Neem Oil (with azadirachtin): repels and disrupts feeding; examples of products: Azamax, Bonide Neem Oil; insect growth regulator and repellent.

4). Insecticidal Soap: good for soft-bodied insects and young larvae; examples of products: Safer Brand Insecticidal Soap; contact kill by disrupting cell membranes.

These products should be available at most gardening centers. Be sure to follow the application instructions on the product labels.

Good Look. Thanks for using our forum