Forest & Grassland Health

Spruce and Larch Bud Moth

Spruce bud moth: Zeiraphera canadensis Mutuura & Freeman, Z. fortunana (Kearfott), Z. unfortunana Ferris & Kruse, and Z. vancouverana McDunnough 

Larch bud moth: Z. improbana (Walker) 

Primary Hosts in Alaska: Spruce (Picea spp.) and larch (Larix spp.) are preferred; true fir species (Abies spp.) are less common hosts. Found throughout spruce and larch forested lands. 

Damage: New needle defoliation that can cause deformed lateral and terminal buds. All tree age classes can be affected. 

Photos

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Photograph of an adult spruce budmoth on a spruce tip Deformed terminal spruce buds caused by spruce budworm Deformed terminal spruce buds caused by spruce budworm Deformed terminal spruce buds caused by spruce budworm
Adult spruce budmoth Spruce budmoth damage Spruce budmoth damage Spruce budmoth damage

Current Status in Alaska (2020 Update) 

Trace amounts of spruce budmoth defoliation in 6 isolated areas were detected in 2020 during ground surveys: 3 sites in the Interior, 2 sites in South Central, and 1 site in Southeast Alaska. In 2019, trace amounts of spruce budmoth defoliation were detected in 2 isolated areas: 1 site in South Central, Alaska and 1 site in Southeast, Alaska. About 50 acres of unknown spruce defoliation was documented during an aerial detection survey in 2019 that could have been the result of spruce budmoth or other spruce defoliators. While spruce and larch budmoths have not been a notable damage agent in Alaska forests recently, they have the potential to defoliate large stands of trees.  

 

Historic Activity 

In 1976, the larch budmoth was responsible for the defoliation of 240,000 hectares (593,000 acres) of larch in Interior Alaska. The trees did not die because defoliation occurred in the spring and the infested larch re-foliated soon thereafter. 

 

Symptoms, Biology, & Impacts 

Larvae of Zeiraphera species can be up to 14 mm long and beige or grey to pale yellow in color with dark brown heads. Adults are small, mottled grey to brown moths with a wingspan of about 10-18 mm. 

Bud moths overwinter on their host tree as eggs under the bark of twigs and branches. Larvae emerge from May through June. Upon emergence the larvae find a suitable bud, bore under the budcap, and begin feeding within the bud. As feeding progresses, larvae characteristically attach the budcap to the bud with silk. Often, multiple larvae feed within a bud. As the bud expands, larvae feed on the new needles. Feeding increases as larval size increases until most of the new needles are consumed. Larvae of some species feed on the new needles of multiple buds on a branch, whereas other species feed within a single bud throughout the entire larval stage. Larvae feed from 3 to 6 weeks depending on the species of bud moth. When larval development is completed, larvae drop to the ground on silken threads where they construct cocoons from pieces of moss, dead needles, soil, and other organic material found on the forest floor. The pupal stage lasts from 18 to 21 days. Adults emerge from late June through July, and females will deposit eggs by late July. There is one generation per year.

Severe infestations may cause reduced growth and deformed terminal and lateral branches. In many cases, the branch curls towards the injured side where larvae have scarred the shoot tissue. Deep scarring makes the shoots fragile and susceptible to breakage. Bud moth damage can also predispose a tree to attack by bark and wood boring beetles and fungal decay.   

The bud moth is not considered a major economic threat to forests. Larvae feed on new foliage and severe infestations may cause reduced growth and deformation of branches, but mortality is limited.

Guidelines for Reducing Damage 

Bud moths are a natural part of Alaskan forests and management of these insects on a landscape scale would be costly and impractical. Individual tree protection for high-value landscape and ornamental trees may be warranted. Physically removing the larvae from the tree by hand can be effective but may not be practical for large trees. Raking and removing the litter beneath trees in late June can help reduce populations by removing the pupal stage of the insect. Use caution with this approach to avoid damaging roots. Chemical control options for bud moths may be available. Timing of applications and coverage of the tree canopy will be important for a successful bud moth treatment. Consult with your local Cooperative Extension Service office for what products are currently registered and effective against bud moths.  

 

Resources and Publications  

Furniss, R. L., & Carolin, V. M. 1977. Western Forest Insects. U. S. Department of Agriculture, Forest Service, Misc. Publ. 1339. p.160-161. Available here.  

Holsten, E. H. 2001. Spruce and Larch Budmoths. USDA Forest Service, Alaska Region, State and Private Forestry. Leaflet R10-TP-97. Available here or here

Holsten, E. H., Hennon, P., Trummer, L., Kruse, J., Schultz, M., & Lundquist, J. 2008. Insects and Diseases of Alaskan Forests. USDA Forest Service, Alaska Region, State and Private Forestry, Forest Health Protection. Publication R10-TP-140, 55. Available here.  

Miller, W. E. 1987. Guide to the Olethreutine moths of midland North America (Tortricidae). United States Department of Agriculture, Forest Service, Agriculture Handbook 660. p1-104. Available here.  

Mutuura, A., & Freeman, T.N. 1966. The North American species of the genus Zeiraphera Treitschke (Olethreutidae). Journal of Research on the Lepidoptera. 5(3) p.153-176. Available here.  

Prentice, R. M. ed. 1966. Microlepidoptera. In: Forest Lepidoptera of Canada recorded by Forest Insect Survey. Dept. For. Canada Publ. 1142. Ottawa: Department of Forestry, Canada. p543-840. 

Pohl, G.R., et al. 2018. Annotated checklist of the moths and butterflies (Lepidoptera) of Canada and Alaska. Pensoft Series Faunistica No. 118. Sofia, Bulgaria. 580 pp. Available here

 

Content adapted from Insects and Diseases of Alaskan Forests (2008) p.55 (Available here) and Spruce and Larch Budmoths Forest Health Leaflet (Available here or here). 

 

For more information about this agent, contact Entomologist Dr. Sydney Brannoch at sydney.brannoch@usda.gov. Content prepared by Dana Brennan, Biological Science Technician, Forest Health Protection, and Jessie Moan, Entomologist, Forest Health Protection. 

 




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