Moths emerge at end of month

Spongy moth (Lymantria dispar) caterpillars finish feeding in July. The insects will then pupate and emerge as adult moths in mid-late July.  Male moths look like many other small brown moths but they can be distinguished by the fact that they fly about looking for females in the late afternoon, unlike other moths, which wait until dark. Female spongy moths are white, 1 1/2 inches long, and although they have wings they do not fly. They are usually found laying an egg mass as in the photo below.  Both the pupa cases and moths can be crushed easily if you can find them.  If you crush a female moth, be sure to use a disposable or washable tool because her pheromone will rub off onto it and attract many male moths.  So do not use your shoe!

Mating disruption is a management technique used to decrease reproduction of spongy moths by preventing male moths from finding females.  This technique works by applying the chemical pheromone (attractant) of the female to an area to mask the natural pheromone levels.  As a result, male moths are overwhelmed by the scent and cannot locate females to mate with.  The chemical pheromone used for mating disruption is highly specific to spongy moths, and is not harmful to humans or other animals.  Two pheromone-based products are currently registered in Wisconsin for mating disruption: Disrupt II (Hercon Environmental) and SPLAT GM (ISCA Technologies).  Both of these products suggest applications approximately two weeks before the emergence of adult moths.  A limitation of this technique is that it is suitable only for low populations of the spongy moth over relatively large areas.  Mating disruption is used by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) to combat spongy moth over larger areas as part of its “Slow the Spread” program, but is not an applicable technique for property homeowners.

Spongy Moth Pupae
Spongy moth adults — brownish male (left) and pale female (right)
Photo Credits: Milan Zubrik, Forest Research Institute – Slovakia, Image 1370017. Forestryimages.org; USDA APHIS PPQ Archive. Image 2652079. ForestryImages.org.