Yellow-headed The yellow-headed spruce sawfly, alaskensis (Rohwer) (: ), By: Cynthia Snyder, Biological Technician, USDA Yellow-headed is a native defoliator of spruce throughout the Forest Service, Alaska Region, State and Private northern United States and Canada. Young open- , Forest Health Protection Program Spruce Sawfly grown trees such as ornamentals in landscape Additional information on this can be plantings, shelterbelts, plantations, and nurseries obtained from your local USDA Alaska Cooperative are especially vulnerable. This insect rarely causes Extension Service office, Alaska State Forestry injury to closed-canopied spruce forests. office, or from: The yellow-headed spruce sawfly attacks all native Forest Health Protection Alaska spruce and most exotic ornamentals State and Private Forestry such as Norway and Colorado blue spruce. Trees USDA Forest Service typically become susceptible to defoliation three to 3301 C Street, Suite 202 five years after planting and remain at risk until a Anchorage, Alaska 99503-3956 height of 18 feet or more is reached. Environmental Figure 1. Adult sawfly. Phone: (907) 743-9455 factors, such as aspect, soil conditions, and temper- ize new needles and then consume them entirely. ature, affect preference and the ability of trees Forest Health Protection Older larvae move on to feed on the previous to tolerate defoliation. State and Private Forestry years’ foliage. If complete defoliation occurs, larvae USDA Forest Service may begin feeding on cortical tissues of the branch 2770 Sherwood Lane, Suite 2A Description and Life History tips. While feeding, the ’s posterior end curves Juneau, Alaska 99801-8545 Adult yellow-headed spruce are small either downward or upward. Disturbed larvae Phone: (907) 586-8883 stingless , approximately 1/3 inch in length. characteristically arch both ends and exude a liquid or: They vary in color from yellowish-brown to nearly from their mouths. black with four shiny, transparent wings (figure 1). Newly hatched larvae are 1/8 inch in length, yel- http://www.fs.fed.us/r10/spf/fhp/fhpr10.htm Adults emerge in spring from late May to mid-June lowish with no markings, with yellow heads that when spruce buds begin to swell. Females deposit become brownish-yellow after feeding (figure 2). eggs singly into shallow slits in the bark of spruce Mature larvae are 3/4 inch in length with a brown The U.S. Department of Agriculture (USDA) prohibits branch tips at the base of the new needles. discrimination in all its programs and activities on the basis of to yellowish-brown head and a dark glossy olive- race, color, national origin, sex, religion, age, disability, political The newly laid egg is very tiny, oblong, pale green green body marked with three gray-green longitu- beliefs, sexual orientation, or marital or family status. (Not all to pearly white, with a thin, transparent, finely dinal stripes along each side and a dark linear spot prohibited bases apply to all programs.) Persons with disabilities stippled shell. Eggs hatch in 4 to 12 days; eggs in just above the base of each leg (figure 3). who require alternative means for communication of program sunny locations take less time to develop than those information (Braille, large print, audiotape, etc.) should contact Mature larvae stop feeding and drop to the ground in shaded locations. USDA’s TARGET Center at (202) 720-2600 (voice and TDD). in mid to late summer, enter the soil surface, To file a complaint of discrimination, write USDA, Director, Duration of larval feeding varies from 30 to 40 and spin cocoons in which they overwinter. The Office of Civil Rights, Room 326-W, Whitten Building, 1400 days. Young larvae immediately begin feeding Independence Avenue, SW, Washington, DC 20250-9410, cocoon is a dark brown fibrous structure approxi- or call (202) 720-5964 (voice and TDD). USDA is an equal United States Prepared by Leaflet gregariously on succulent new foliage. Small larvae mately 1/2 inch in length, with one end slightly opportunity provider and employer. Department of Forest Service R10-TP-120 consume only small parts of the new needle. As larger and blunter than the other, with soil particles Agriculture Alaska Region August 2003 the larvae develop, however, they first skeleton- adhering to it. Larvae do not pupate immediately Newly emerged females directly to host trees taken to maintain the vigor of planted spruce trees Photography Credits and search for suitable egg laying sites, with a pref- to minimize impact. Cover photo: The University of Alaska Fairbanks erence for spruce growing in full sunlight. Mating is Many natural predators feed on sawfly larvae, Cooperative Extension Service, Anchorage, AK. not required to initiate oviposition, although non- including birds, rodents, spiders, and . Since mated females produce only male offspring. Male Figures 1–3: The University of Alaska Fairbanks cocoons are buried in the soil, a certain amount of adults hover around host trees and search foliage to Cooperative Extension Service, Anchorage, AK. predation by rodents such as mice and shrews as locate females. The sawfly completes one genera- well as ground beetles may be expected. Several tion per year. species of and fly parasites are known to Yellow-headed spruce sawfly larvae may be infest sawfly eggs and larvae. Parasitized eggs can confused with spruce budworm larvae. However, be recognized by their black color. However, pred- budworm emerges much earlier and spins a con- ators and parasites are not effective controls when spicuous web around feeding larvae. environmental factors are favorable for this insect. When larvae are found, several alternative methods Damage Caused of control can be applied: The yellow-headed spruce sawfly is not considered  Handpicking the larvae from foliage may be Figure 2. Young sawfly larva, note the yellow head. a major forest in Alaska; however, aesthetic a viable alternative for control for ornamental value of ornamental trees can be greatly affected. after cocooning, but remain as prepupae for several trees. months. The advent of warm weather the follow- Young larvae feed exclusively on the current year’s  Caution: Pesticides can be injurious to humans, ing spring initiates the development of the pupae needles resulting in loss of the most photosyn- For large infestations, a mixture of one tea- thetically active tissue. Once new growth is eaten, spoon dish soap per gallon of water can be domestic , desirable plants, and fish or and emergence of adults from the cocoons. Some other wildlife—if they are not handled or applied individual prepupae may undergo prolonged pre- older larvae move on to previous years’ needles. used in a high pressure spray to knock larvae Damage first appears most intense in the upper from the tree and interfere with the respiration properly. Use all pesticides selectively and care- pupal diapause for two or more years as a survival fully. Since approved uses of a pesticide may mechanism in unpredictable environments. crowns of infested trees, where the remaining, of the remaining . partially chewed, needles impart a brownish color change frequently, it is important to check the  It has been suggested that the crowns of label for current approved and legal use. and ragged appearance to the tree. As larvae move severely infested trees be pruned to encourage on to the older foliage, the entire tree may become new growth. Follow recommended practices for the disposal defoliated. Heavy defoliation for a single year of surplus pesticides and pesticide containers. causes reduction of shoot and needle growth, two  Chemical control has been necessary in some Mention of a pesticide in this publication does or more years may result in branch dieback, topkill, cases, especially plantations, shelterbelts, not constitute a recommendation for use by the and possibly tree death. and nurseries. Correct timing is critical to the USDA, nor does it imply registration of a prod- effectiveness of the product used. Spraying uct under Federal Insecticide, Fungicide, and Guidelines for Reducing Damage should occur after bud-break, when damage Rodenticide Act, as amended. Mention of a pro- is first noted, prior to the emergence of natural prietary product does not constitute an endorse- Environmental factors affect the ability of trees to enemies, such as parasites. tolerate defoliation by the yellow-headed spruce ment by the USDA. sawfly. Environmental stresses, including soil com- Check with your local Cooperative Extension paction, poor nutrient availability, and water stress, Service office for insecticides that are currently may all increase host susceptibility. Care should be registered for sawfly control. Figure 3. Mature sawfly larva feeding on needles.