Hosts: Engelmann spruce, subalpine fir
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.
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.
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.
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.