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Croesus latitarsus

Dusky birch sawfly caterpillars. Photo: Lacy L. Hyche, Auburn University, Bugwood.
Scientific Name: 
Croesus latitarsus
Common Name: 
Dusky Birch Sawfly
Growing Degree Days (GDD's): 
1200–2200 GDD's, Base 50F, March 1st Start Date (Source: Robert Childs, UMass Extension.)
Host Plant(s) Common Name (Scientific Name): 
Birch (Betula spp.)
Black birch (Betula lenta)
Gray birch (Betula populifolia)
Japanese white birch (Betula platyphylla)
Paper birch (Betula papyrifera)
Red birch (Betula occidentalis)
River birch (Betula nigra)
Yellow birch (Betula alleghaniensis)
Insect Description: 

One or two generations occur per year. Winter is spent as a prepupa in a cocoon in the soil. Pupation occurs in the spring time, and adults emerge in May. Eggs are laid and larvae occur from April-May (1st generation) and again in mid-July to mid-September (2nd generation). Larvae have a black head capsule and are generally yellow in color with black markings and may reach up to an inch in length when fully grown. Larvae sit in an S-posture (rear-end out) when alarmed or not feeding. If there is a second generation, adults may emerge again from mid-July to mid-September. Adults are approximately 1/2 inch in length and look like black wasps. 

Damage to Host: 

Foliage of birches, primarily gray birch, but also black, yellow, and paper birches is consumed. Small trees may be defoliated by these caterpillars that feed in groups, particularly around leaf margins. 

Monitoring: 

Look for leaves eaten from the edge working inward. Search the margins of those leaves for sawfly caterpillars. Remember, sawfly caterpillars typically have 6 or more prolegs. 

Cultural Management: 

When found, drop caterpillars into a can of soapy water or prune out and destroy the branch section they are feeding on. This may be particularly effective on smaller trees where isolated populations can be mechanically destroyed without chemical intervention. Reportedly, numbers of this species rarely reach levels where chemical intervention is necessary.

Natural Enemies & Biological Control: 

None reported specific to this species, but other sawflies in this same genus have reportedly been parasitized by Compsilura concinnata and other parasitoids.

Chemical Management: 

Acephate (NL)

Azadirachtin (larva only) (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: 

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), and imidacloprid (soil drench).

When used in nursery setting, 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".