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Gypsy Moth Program
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Robert Bloom
West Nile Virus Coordinator

Gypsy Moth Outlook 2016

Every June, the PA DCNR gives annual regional briefings on the state’s gypsy moth situation. The Centre County Director of Planning and the GM Coordinator attended the 2016 briefing to assess the likelihood of future outbreaks in our county in 2017 and onwards.

The DCNR Bureau of Forestry specialists were unanimous in their opinion that there will be no gypsy moth activity in Centre County in 2017. Moreover, because there are no gypsy moth populations in adjacent counties, it is very likely that we will be clear of gypsy moths in 2018 as well.

Although the 2015/16 survey of gypsy moth egg masses indicated medium-sized populations in neighboring Mifflin and Huntingdon Counties, the weather we experienced in April and May 2016 greatly stressed the gypsy moth populations, which collapsed completely. A warm dry April led to an early hatch. This was followed by three weeks of cool wet weather in May, resulting in a slow leaf expansion, which limited food to caterpillars. The rainy weather also resulted in a major expansion of pathogenic fungal activity (see below). The population collapse was so complete that DCNR foresters saw no difference between the sprayed areas and adjacent unsprayed areas that had been infested to a similar degree.

The Reduced Threat of Gypsy Moths in Recent Times

When gypsy moth outbreaks in the northeastern US over the last four decades are analyzed, it is clear that over time, the severity of the outbreaks has been greatly reduced both in terms of the affected area and in terms of their longevity. The reason is the rapid spread of a gypsy moth-specific fungal pathogen (called Entomophaga maimaiga) which was introduced from Japan in 1910, but for unexplained reason was not active until 1989. It is now endemic in all gypsy moth populations and acts as a very effective natural control agent.

It appears that the fungal pathogen is becoming more effective as time progresses. In 2013, western counties in the state that had not been infested by gypsy moths for over twenty years (and so had few, if any fungal spores) had a large population build-up that was expected to last for three years. Instead, the fungal pathogen caused populations to crash that same year.

Are We Now Fully Protected from Gypsy Moths in Centre County?

Short answer: No. A series of two or three dry springs could tamp down the activity of pathogenic fungus and allow the low background gypsy moth population (which is always present in low numbers) to expand exponentially, increasing its numbers a hundredfold each season until it becomes a major outbreak.

Despite the hostile pathogenic environment for gypsy moths, some of the eastern counties in PA had dense populations as high as 30,000 egg masses per acre in 2016. To put that number into context, keep in mind that DCNR considers an egg mass count of 250 as risky to foliage and therefore qualifying for their spray programs. At time of writing, we don’t know whether these high populations collapsed like many others this year.

What Do I Do If I See A Gypsy Moth?

First, positively identify the caterpillar as a gypsy moth – google ‘gypsy moth’ for pictures. If the caterpillars are forming webs on the tips of branches, they are definitely not gypsy moths!

Gypsy moths are always present in Centre County at low levels, so you should expect to see the odd caterpillar. However, if you see many GM caterpillars and especially if you see that they are defoliating foliage, please report this to the contact name at the top of this page who will pass on the information to the county’s volunteer GM coordinator.

Updated June 16, 2016