Forest Insect Defoliators
FIELD GUIDE TO INSECTS AND DISEASES OF ARIZONA AND NEW MEXICO FORESTS
Nepytia janetae
(Rindge)

Hosts:  Engelmann spruce, subalpine fir

Figure 3. Adult western spruce budworm with pupal case.Symptoms/Signs:  Larvae of this insect feed on foliage, chewing needles of all ages. Defoliation can be light to heavy. Partially consumed needles can be found beneath the trees. Mature caterpillars are approximately 2.5 cm in length. The upper surface of the larva is gray with dark brown and green markings in a herringbone pattern and with irregular pale cream lateral stripes. The head capsule is mottled with a distinct black stripe above the mouthparts. These larvae can be seen in the foliage, hanging from silken threads, beneath the tree on ground or snow and climbing up the bole of the tree. Adults are small light gray moths that can be seen flying singly through the woods or flying in large numbers around the tops of host trees. Pale green pupae or empty pupal cases can be seen on the foliage wrapped in webbing. Mummies of parasitized larvae can be seen in the foliage attached to needles.

Figure 40. Larva (looper) of Nepytia janetae.Biology:  N. janetae has one generation per year. Adults appear in late June, peak flight is reached in early July. Eggs hatch in late September. Larvae feed throughout the winter and spring. Some are present in larval form until early July. There is considerable overlapping of life stages.

Figure 41. Defoliated fir caused by Nepytia janetae in the White Mountains, Arizona.Effects:  During outbreaks, spruce-fir stands can be heavily defoliated resulting in growth loss and, with multiple years of defoliation, tree mortality. Mortality can be due to defoliation alone or due to secondary infestation by spruce beetle and western balsam bark beetle. This insect caused extensive damage and mortality to spruce and subalpine fir in the White Mountains and Pinaleño Mountains of Arizona in the late 1990s. Associated spruce beetle mortality occurred only in the Pinaleño Mountains.

Figure 42. Near view of fir defoliated by Nepytia janetae in the White Mountains, Arizona.Similar Insects and Diseases:  Although there are similar insects in other regions (e.g. western hemlock looper and western false hemlock looper), none have been observed in the Southwest.

References:  56, 80