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Green Spruce Aphid (Elatobium abietinum)

Trees Affected

Common: Spruces

Occasional*: True Firs, Siberian Larch, Eastern White Pine, Scotch Pine, Douglas Fir

*Only during outbreaks

Summary 

The green spruce aphid is a small (1-2mm), green insect that is almost exclusively found on spruce species (Picea). Green spruce aphids are a non-native, invasive species that stunt growth by defoliating parts of the tree and can cause significant mortality outside of its native range. Feeding can be spotted in 5-10 days on Sitka spruce by yellow spots on the needles which can lead to whole needle discoloration and defoliation. The aphids generally feed on older needles and branches and avoid any new growth, so another sign of this pest is defoliation of all but the current season’s needles. On younger trees (< 5 years), the aphids primarily feed on the upper canopy, while in older trees they attack shaded areas, which are generally on the lower portion of the tree. Like many aphids, the green spruce aphid produces honeydew, which facilitates the growth of a sooty mold on the host trees’ stems. When present, this sooty mold is helpful for positively identifying the green spruce aphid. Shaking affected foliage over a piece of white paper to see if green aphids fall onto it is another common method of detection.

Local Distribution 

The local distribution of this insect is unknown, but appears to be widespread. Trees with symptoms consistent to those produced by green spruce aphids have been found along Highway 101 near Humboldt Lagoon as well as in some areas of Ferndale.

Management Strategies 

Since spruce is not a valued timber species in the United States, little research has been done on how to manage the aphids in coastal California. Introduction of predators of this aphid has not produced notable declines in their population. Due to the widespread impact of green spruce aphids in this region, the use of insecticides is not recommended, as the impact on the ecosystem is far greater than the success rate of using the insecticide. Although healthy, vigorous trees tend to host a larger population of these aphids, they also sustain less damage than less vigorous trees. Therefore, reducing stressors and improving tree vigor are still beneficial for managing the effects of this insect even though doing so will not eliminate a population entirely.

Pests and Pathogens with Similar Symptoms

Giant Conifer Aphids (Cinara spp.): Aphids in this genus feed on sap from roots, twigs, and branches of various conifer species. Although they are aphids and share a basic body plan, they are much larger than green spruce aphids (5-6 mm in length) and dark brown or black instead of green. They are also frequently mistaken for ticks, so if your aphid looks like a tick, it’s likely a giant conifer aphid and not a green spruce aphid.

Further Reading

Description with distribution map, aphid biology, and management strategies:

https://www.cabi.org/isc/datasheet/30897#tosymptoms

Description of the aphid. Note that risk and management sections are written for a European setting and may not be accurate to local forests and conditions :

https://www.forestresearch.gov.uk/tools-and-resources/fthr/pest-and-disease-resources/green-spruce-aphid-elatobium-abietinum/