Amauronematus azaleae

Azalea sawfly caterpillar. Photo: Jeff Hahn, University of Minnesota.
Scientific Name: Amauronematus azaleae
Common Name: Azalea Sawfly
Growing Degree Days (GDD's): 280–1000 GDD's, Base 50F, March 1st Start Date. (Source: Robert Childs, UMass Extension.)
Host Plant(s) Common Name (Scientific Name)
Azalea (Rhododendron spp.) 
Insect Description:

One of at least 3 sawfly species known to feed on azalea in the eastern US. Larvae feed on the edges of the leaves. One generation per year. These caterpillars are green with an amber colored head and various tiny black spots. Larval development complete by July 1 in Massachusetts and they grow to approx. 0.39 inch long. Adult females are wasp-like insects that lay their eggs on expanding spring foliage. Once mature, larvae drop to the soil to pupate.
Damage to Host:

Sawfly larvae will feed on the edges of azalea leaves and may defoliate the plant, leaving only midveins behind at times.
Monitoring:

Look for tiny, green sawfly caterpillars feeding on the edges of leaves. 
Cultural Management:

If caterpillars are low in numbers and caught before the damage to the plant is too severe, these insects may be removed with a gloved hand and squished or dropped into a can of soapy water.
Natural Enemies & Biological Control:

None known at this time.
Chemical Management:

Acephate (NL)

Azadirachtin (larva only) (NL)

Bifenthrin (NL) 

Bifenthrin+imidacloprid (L)

Carbaryl (L)

Chlorpyrifos (N)

Cyfluthrin (larva only) (NL)

Deltamethrin (larva only) (L)

Dinotefuran (larva only) (NL)

Emamectin benzoate (L)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (L)

Horticultural oil (larva only) (L)

Imidacloprid (larva only) (L)

Insecticidal soap (larva only) (NL)

Lambda-cyhalothrin (L)

Pyrethrin+sulfur (larva only) (NL)

Spinetoram+sulfoxaflor (larva only) (N)

Spinosad (larva only) (NL)
Notes:

Treat when larvae appear. 

To entomologists, the term caterpillar refers to the immature or larval life stage of the Lepidoptera - butterflies and moths. However, the public and some entomologists included sometimes use this term interchangeably to refer to the immature or larval life stage of certain Hymenoptera - in particular, sawflies. 

This can cause confusion when selecting management options for pests collectively referred to as caterpillars. The larvae discussed here will mature into an adult sawfly. This means that the active ingredient Bacillus thuringiensis Kurstaki (Btk) will not be effective at managing this insect. Btk will only kill the caterpillars of moth (or butterfly) pest insects. It will not kill sawfly larvae. 

Sawfly larvae can be distinguished from moth or butterfly caterpillars by the presence of or absence of 6 or more prolegs. Some sawfly species will have 6 or more pairs of fleshy abdominal prolegs, whereas some sawfly larvae will have 0 pairs of fleshy abdominal prolegs. Caterpillars that mature into butterflies or moths will have 5 or fewer pairs of fleshy abdominal prolegs. Prolegs are soft, and found behind the hardened 3 pairs of thoracic legs on the insect. In butterfly or moth caterpillars, the prolegs will also have tiny hooks or crochets on the very bottom.

Active ingredients that may be applied systemically include: acephate (injection), azadirachtin (injection, soil drench), dinotefuran (soil drench), emamectin benzoate (injection), and imidacloprid (soil drench).

When used in nurseries, chlorpyrifos is for quarantine use only.

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: September 27, 2024. To check current product registrations in Massachusetts, please visit the MA Department of Agricultural Resources Pesticide Product Registration page and click on "Search Pesticide Products Registered in Massachusetts - Kelly Solutions".