Poplar Clearwing Borer: How to Control Them Naturally

Poplar Clearwing Borer

Paranthrene dollii

A wasp-like moth whose caterpillars tunnel into the lower trunk of poplars, cottonwoods, and willows.

How to control poplar clearwing borer

Use: Scanmask Spray (also works: Ecomask Spray, Scanmask Topdressing, Ecomask Topdressing)
When: Anytime the borers are active.
Where: The lower trunk and the bark at the soil line until wet, especially around active holes, and the soil right at the trunk base.

What it looks like

Adults are clearwing moths with yellow and black bands that look like wasps or hornets. Larvae are whitish caterpillars with a brown head, up to 1.5 inches long. It is also called the cottonwood clearwing borer. The name is also used for the hornet moth (Sesia apiformis), a close look-alike.

Damage

Larvae tunnel under the bark and into the wood at the base of the trunk and in large roots. Frass and sap show at the holes. Weakened trees can break off at the ground.

How nematodes help

The caterpillars live in the lower trunk and large roots, near or just below the soil line. The pupae sit in the tunnels near the bark.

No studies on these two species were found. In a lab study on a related poplar clearwing (Paranthrene diaphana), S. feltiae (the nematode in Scanmask) killed the most, followed by S. carpocapsae (the nematode in Ecomask), then H. bacteriophora (the nematode in Heteromask). In field trials, spraying S. feltiae on tree trunks controlled 77 to 84% of related clearwing borers.

In university research, the timing that worked best was spring, and late summer to fall, when the caterpillars are active and the frass (sawdust-like droppings) is fresh, about April to October.