Nun Moth

Techniques to Identify Each Life Stage and Differentiate it From Gypsy Moth 

Research Issue

The risk of nun moth accidentally being introduced to North America is thought to be high.  Regulatory officials need a good guide for identifying all stages of this insect and differentiating it from gypsy moth, a closely related species.

Our Research

The literature was examined and each stage of the nun moth was photographed.  Each stage of the nun moth and gypsy moth were compared.  Diagnostic characteristics were documented.

Expected Outcomes

Guide for use in identifying nun moth and differentiating it from gypsy moth.  The pest alert is out of print but available on the web.  Port inspectors all have copies and several specimens of nun moth have been preserved and made available for reference. 

Research Results

Eggs

Eggs of  Lymantria monacha are spherical, ~ 1 mm in diameter, slightly depressed in the middle of the upper surface and often flattened on the lower surface.  The eggs are orange brown (blue green if reared on artificial diet) at first, later turning brown with an opalescent shine.  The eggs are deposited in clumps that are glued together without a covering of hair.  The female does not deposit all of her 70-300 eggs in one place and generally hides them in crevices in the bark of trees. 

Larvae 

The hairy larvae of the Lymantriidae can always be distinguished from other families by the presence of some type of dorsal eversible glands, prominently located in the middle of the 6th and 7th abdominal segments.  Larvae of Lymantria species have a full complement of low, rounded verrucae, without dense hair tufts, and usually without hair pencils.  The dorsal verrucae bear needle like setae and sometimes longer hairs.

Newly hatched larvae are ~ 4 mm long.  At first, they appear tan but within several hours they turn black.  They are very hairy and have "air hairs" which may aid in dispersal.  The "air hairs" are simple setae with a bulb-like structure in the middle that looks like a water droplet under the light microscope.  The "air hairs" are only present on the 1st instar larvae.  

The 2nd instars appear black with a few lighter spots and have two white patches that almost encircle each dorsal verrucae on the 3rd thoracic segment but do not meet along the middorsal line.  There is also a light patch which fills the middorsal space between the verrucae from the middle of the 4th to the middle of the 6th abdominal segments.  The larvae have small-paired glands on 1st 5th abdominal segments and large single orange eversible glands on 6th and 7th which are clearly visible.

From the 3rd instar on, the head of the larva is orangish brown with numerous brown and black freckles.  The middorsal stripe is a mottled brown to black.  The dorsal verrucae of the larva are all bluish.  The dorsal spot or patch patterns present in the 2nd instar persist through the later instars.  The mature larvae appear tanish, greenish or dark grayish in color with extensive brown or black mottling and are 30 to 40 mm in length.  The color of the larvae conceals them when they rest on the branch of a conifer.

Pupae 

The pupa has no cocoon, is reddish brown, and shiny with light colored (occasionally red) clumps of hairs.  It measures 18 to 25 mm in length.  The sex of the pupa can be determined by the form of the bases of the antennal pads and by the characteristics of the future sex organs located on the external ventral portion of the abdominal segments (female on 8th segment and male on 9th).

Adults  

Lymantrid adults can usually be recognized by the position of the Sc vein relative to Rs vein in the hindwing, the base of the M2 vein being much closer to M3 than to M1 in the hindwing, the absence or vestigial nature of the haustellum, the absence of ocelli, the prespiracular counter tympanal hood, and the one to three long, divergent spinules at the end of each antennal branch (Ferguson 1978).

In Lymantria species, the females have wings that are longer and narrower than those of the male.  Female bodies are stout and antennae are bipectinate with short branches approximately the thickness of the shaft, each bearing one terminal spinule.  Male antennae are bipectinate with very long branches, each bearing one long terminal spinule and sometimes a second very short one.  Sexual dimorphism in form and color is often extreme.  When at rest the outline of the female is that of an isosceles triangle while that of the male resembles an equilateral triangle.  

Sexual dimorphism in color is much reduced in Lymantria monacha.  The forewing coloration of both sexes varies from characteristic chalk white, decorated with numerous dark transverse wavy lines and patches, to almost black specimens.  The hind wings are generally gray brown with minute dark and/or light patches at their edge.  The female has a wingspan of 45 to 55 mm while the male has a wingspan of 35 to 45 mm.  Lighter colored females have abdomens with patches of pink or red and black bands, which correspond to the intersegments.  Darker colored females have abdomens that are all dark.  The darker forms are common in Europe but totally absent in Oriental populations.  The female has an extremely long ovipositor adapted for its specialized egg laying habit.  

SIMILARITIES TO OTHER SPECIES OR CONDITIONS  

Newly hatched larvae of both Lymantria monacha and Lymantria dispar are very similar.  The L. monacha 1st instar can be distinguished from the L. dispar 1st instar (10-20X) by the presence of paired black pinaculi on the dorsal surface of the body.  Each pair of pinaculi is located in front of and between the pair of dorsal verrucae on each segment.  Under a scanning electron microscope additional differences become evident.  The L. dispar larva has a single plumose seta with virtually no pinaculum located in the same position as the L. monacha "air hair" with a large pinaculum.  Keena et al. (1998) provide a complete description of how to distinguish all stages of L. monacha from L. dispar. 

Keena MA, Shields KS, Torsello M. 1998. Nun moth: potential new pest. Pest Alert NA-PR-95-98. U.S. Dep. Agric. For. Serv., Northeastern Area, State and Private Forestry. 2 p.

Research Participants

Principal Investigators

• Melody Keena, USDA Forest Service- Northern Research Station Research Entomologist
• Kathleen Shields, USDA Forest Service- Northern Research Station Research Entomologist (Retired)
• Mary Torsello, USDA Forest Service- Northeastern Area State and Private Forestry

For further details log on website :
https://www.nrs.fs.fed.us/disturbance/invasive_species/nun_moth/risk_detection_spread/identify_life_stage/