HEMLOCK LOOPER
Lambdina fiscellaria (Gn.)

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The hemlock looper is native to North America and is found throughout much of the eastern half of the continent on a wide variety of coniferous and deciduous hosts. It is a serious pest of balsam fir in Quebec and the Maritime Provinces of Canada. Hemlock looper caused serious, but small scale, defoliation in some parts of Maine in the 60's, but it did not become a major problem in Maine until the late 80's and early 90's when severe hemlock and fir defoliation expanded to a quarter million acres over the southern half of the state. Stands of balsam fir and white spruce were killed along Maine's coast early in the outbreak. Inland hemlock stands were severely defoliated later in the outbreak and some experienced scattered but significant mortality. Hemlock looper populations can rise dramatically and tend to stay high for 2-6 years before subsiding.

Hosts

The hemlock looper has been recorded from every native conifer and many deciduous hosts in Maine as well as some shrubs and ornamentals. Hemlock, balsam fir, and white spruce are most at risk.

Damage

Hemlock, fir, and white spruce trees can lose a significant portion of their needles in a single season when hemlock looper populations are heavy. Trees that lose more than 70% of their total needle compliment usually experience long term effects such as branch, top, and even some tree mortality. Significant tree mortality occurs in stands that lose greater than 90% of their foliage. Heavy looper populations can kill conifers in one season but usually mortality occurs in stands defoliated for several seasons. Deciduous hosts are much less affected by looper and rarely experience significant damage.

Hemlock Looper Larva
Photo: Maine Forest Service, Forest Health & Monitoring, Slide Collection

Life Cycle and Description

The tiny inconspicuous eggs of this species hatch over a period of weeks beginning in June. The looper larvae feed briefly on new foliage and then retreat to older foliage. The larger larvae are very messy feeders, moving about "nipping" foliage (which later dies) and, when disturbed, dropping from the trees onto undergrowth where defoliation is often heaviest. Although much of the defoliation by mature larvae occurs on older foliage, when this is gone new foliage may be stripped as well. The ground beneath heavily infested trees may also be covered with a mat of "nipped" or partly chewed needles. In late July, larvae begin seeking out protected spots to pupate. The variable, brown and green, spotted pupa has no cocoon and is formed in cracks and crevices on the tree bole, objects nearby or in the litter. By mid-August, after a pupal period of 2-3 weeks, the frail, tan moths begin to appear and flutter about. In heavily infested stands it is not uncommon to find large numbers of moths resting on trunks of trees and on low deciduous vegetation. These fly readily when disturbed. Moths are present from mid-August to October. Mating takes place on resting sites and "coupled" pairs of moths often show different color variations. The very tiny eggs are deposited singly or in small clusters on foliage, twigs, bark, understory vegetation, debris or in the litter.

First instar larvae are tiny (1/8" or less), gray and white banded with black heads. The larvae go through a series of four molts, changing with each molt. Their head changes from black to gray following the first molt (the second instar) while the body color remains similar. Following the second molt (the third instar) the body darkens and begins to gain the more typical banded and spotted pattern of mature larvae. In the last, or fifth instar, most larvae are roughly 1.25" in length and 1/8" or more across. At this time larvae range in color from nearly black through light green to straw yellow. All, however, have a broad, distinct and usually lighter band down their back containing paired (4 per segment) dark spots and have a light underside. Two pair of dark spots are also evident on the top of their head. Although the color intensity may vary widely within the species, most moths are basically dark straw yellow with a variable dusting of tan or brown to brownish purple scales. Each forewing has an angular, often darker, band set off by two narrow dark lines. A darker spot is also usually visible in the center of this band on each forewing. When at rest, these moths lay very flat in a broad wedge shape.

Recommendations

Advice should be sought as to a course of action in forested areas. Based on observations made during the recent outbreak, pesticide control is rarely necessary to protect commercial forest stands. Pesticide treatments may be warranted to protect high value residential or recreational properties especially near bodies of water and when stands are on shallow, ledgy soils. The need for control would be based on desired results (aesthetic or simply protection) and previous defoliation or stress. Use the population assessment described below to determine if and when there are enough larvae present to warrant control.

Growers of Christmas trees and wreath brush are advised to assess hemlock looper populations to determine if treatment is needed.

Population assessment :

Beginning June 1, susceptible softwood should be randomly checked on a weekly basis through July 1 using a 3x3 square cloth beating frame (simply tack a piece of white muslin or sheeting to some form of stable light wooden frame). Carefully insert the frame into the canopy so that it remains flat and beneath a 3 ft. branch. While holding the beating frame with one hand, gently rap the entire branch with a light stick or rod in your other hand using a downward motion toward the sheet.

If loopers are present, they should then fall on to the sheet. Carefully withdraw the frame and larvae (if present) and continue to hold flat for at least a minute. Hemlock loopers play "possum" and often will not move for a minute or two. If loopers are present they will, however, begin to rear up and wave about or move within a couple of minutes. Remember that these early larvae are tiny (see description). If you're unsure that the insects you observe are indeed hemlock looper, save some larvae in alcohol and send them in for positive identification.

Count the number of larvae on the sheet. A beating yielding one to five larvae would probably indicate low defoliation except where the trees were heavily defoliated the season before. Five to ten larvae per sample could produce noticeable feeding damage in the current season. Hemlock would be more likely to suffer permanent injury than other species. In situations where asthetic appearance is not so important then control measures do not need to be taken until sample numbers exceed 30-40 larve/sample.

Control decisions for individual Christmas tree plantations should be determined for each situation. Should native fir and/or hemlock in the adjacent area be heavily defoliated and larvae be found in monitoring checks, growers should seek more advice.

Control*

The preferred pesticide registered for use against the hemlock looper is Bacillus thuringiensis (B.t.). B.t. can be used for both aerial and ground applications but requires careful timing. It is critical that you have early detection for looper if you plan to use B.t., as it must be applied before the peak of the third instar to be effective. Larvae at this point are still small (less than 1/2" long).

For growers of Christmas trees and wreath brush it is necessary to achieve a more rapid control of such defoliators than usually achieved by B.t. Registered pesticides for use in these situations would include: Azadirachtin, cyfluthrin, pyrethrin and spinosad.

*NOTE: These recommendations are not a substitute for pesticide labeling. Read the label before applying any pesticide. Pesticide recommendations are contingent on continued EPA and Maine Board of Pesticides Control registration and are subject to change.

Caution - For your own protection and that of the environment, apply the pesticide only in strict accordance with label directions and precautions.

MAINE DEPARTMENT OF AGRICULTURE, CONSERVATION AND FORESTRY
Maine Forest Service - Forest Health and Monitoring Division
January 2001

For More Information:
USFS PestAlert