Gypsy Moths

Gypsy Moth Caterpillar on Fothergilla gardenii – a face only a mother could love. This gypsy moth is responsible for large missing sections in the Fothergilla leaves, those smaller holes and discoloration are from 4-lined plant bugs.

Gypsy Moths

Since I learned a lot more about moths by participating in National Moth Week events in years past I have become obsessed. I sit out at my porch light each night trying to identify the moths resting on the screen door (and the spiders there to eat them) and marveling at the diversity and beauty of this night time wildlife.

One moth I am obsessed with but for different reasons is the Gypsy Moth (Lymantria dispar). Causing damage to millions of acres of forest yearly, these introduced insects are worth getting to know.

Recently I was heading out the door on my way to work and notice large frass (insect larvae excrement) on the top rail of my front porch. A closer inspection revealed chewed leaves on the Fothergilla above the railing.

Frass and chewed leaves evidence of Gypsy Moth Caterpillar.

A quick look at the shrub revealed just a couple large (bigger than I have ever seen) Gypsy Moth caterpillars. How do I know they were Gypsy Moth Caterpillars?  Gypsy Moth caterpillars have distinct markings separating them from other caterpillars. In the photo you will notice the back of the caterpillar covered with dots. Notice how the first 5 pairs of dots on the back of the caterpillar are blue and 6 pairs are red? That is the tell-tale sign of a Gypsy Moth larva.

The distinctive Blue and Red pairs of dots identify this caterpillar as Gypsy Moth Larva.

Controls:

Gypsy Moth larva can devastate a forest. Found to feed on hundreds of different species of plants and favoring oaks and aspens, they are a threat to Pennsylvania forests and landscapes.  Caterpillars are just one stage in the life cycle of the Gypsy Moth. The caterpillar stage seems to capture our attention because of the damage to our trees, it is important to become familiar with the various stages of Gypsy Moth so you can make appropriate control decisions.

Here you see pupal stage (shiny dark brown cyclinders), egg masses (tan masses) and male (dark) and female (White) adult moths.

I hand-picked the larvae from my Fothergilla and dispatched them using the squish method. Smaller infestations on shrubs can be handled  this way. Larger infestations tend to happen regionally and in cycles and can be addressed in other ways. A general rule of thumb is that up to 30% loss of foliage will not cause significant harm to the plants. If there is more than 30% defoliation on trees and shrubs, management options should be considered. Some years there are bumper crops of Gypsy Moths and other years they are less of a problem.

Small mammals have been found to eat the larva.  Birds tend to stay away because of the spiny hairs that coat the caterpillar body.

There are some naturally occurring viruses and fungi that will kill Gypsy Moth larva and help control the population.

Gypsy Moth “wilt” is caused by one such virus. This virus accumulates in plant material which is then ingested into caterpillars as they feed on foliage. When the infected caterpillars die, the virus invades the soil and continues to inoculate plant material. This virus doesn’t do much to control small Gypsy Moth populations, but during those population explosions the virus will spread rapidly and help control forest devestation. This naturally occurring virus complex has been extensively researched and has been developed into “Gypchek”. Produced by the National Forest Service, Gypchk controls only the caterpillar stage of Gypsy Moth and doesn’t effect any other type of caterpillar. Gypchk is used as a biological insecticide through aerial or ground applications.

Gypsy Moth “wilt” caused by a nucleopolyhedrosis virus.

Gypsy Moth “wilt” caused by a nucleopolyhedrosis virus.

Two naturally occurring fungi may also control Gypsy Moth populations. – Entomophaga maimaiga – may control heavy infestations during wet springs. Another control option is a naturally occurring fungus – Btk (Bacillus thuringiensis var. kurstaki). This can also be used to control Gypsy Moths and is available commercially. Btk works on Gypsy Moth larva and a variety of other butterfly and moth larva. When using Btk, one must be aware of other non-target butterflies and moths in the area. Btk should be applied while the caterpillars are actively feeding as it is a stomach poison and needs to be ingested in order to be effective.

There are also many chemical insecticides labeled for control in a variety of landscape and forest conditions. According to the Penn State Entomology Gypsy Moth fact sheet these should be applied in May after most of the egg masses have hatched and the larvae are still small.

As with all pesticides, be sure to follow all label instructions when applying these products.

Penn State Extension is looking to learn more about Gypsy Moths in order to monitor for control decisions. If you are a resident of York County, check out this opportunity to contribute to science.

You should get to know more about moths too. They are not all like the Gypsy Moth, invaders from other countries destroying our forests. Many are harmless, some are beneficial pollinators and some are just as beautiful as butterflies. National Moth Week is July 18 – 26 and there are workshops and night viewing programs happening around the country. Bring your family, bring your friends, check out the wonder of nighttime diversity and get to know your local moths – the good and the not-so-good.