Southwestern Region

FOREST HEALTH: High Elevation Looper Activity in the Region

In the last decade we have observed outbreaks of a few native defoliators in our Southwest high elevation forests that have not previously had recorded outbreaks. These defoliators are primarily geometrids (also called inchworms or loopers).

In the mid to late 1990s, an outbreak of a little known looper, Nepytia janetae, caused considerable defoliation and resultant mortality on Mount Baldy in the White Mountains of Arizona. This insect was also credited with damage and mortality in the Pinaleño Mountains in the 1990s and the Sacramento Mountains in New Mexico in the mid-2000s.

The latest outbreak is being caused by a looper called the Mountain Girdle, Enypia griseata, now defoliating spruce and fir trees also on Mt. Baldy. The common name presumably refers to the shape of the lines on the adult forewings that reminded someone of the shape of a woman’s girdle. This insect is known to occur from Arizona into Canada. The defoliation in Arizona was first recorded on 500 acres during our 2007 aerial detection surveys. Looper larvae were observed feeding on spruce and fir trees. It has been described as innocuous in other areas where it is endemic, but we are seeing tree mortality especially in spruce where heavily defoliated trees are then attacked and killed by spruce beetle, Dendroctonus rufipennis. Aerial detection survey in 2008 showed that the impacted area had increased to 2,355 acres. Study plots have been initiated to determine the impacts and biology of this insect in Arizona.

Aerial view of defoliation impact on Mt. Baldy. The mortality is a result of the 1998-1999 Nepytia outbreak.