Giant conifer aphids
Order: Hemiptera
Family: Aphididae
Description
Cinara spp. are commonly referred to as giant conifer aphids and collectively feed on pines (Pinus spp.), juniper (Juniperus spp.), and spruce (Picea spp.). There are about three dozen species inhabiting the Rocky Mountain region. These aphids have long legs and measure about 6.5 mm (1/4 inches) long, making them relatively large compared to other aphid genera. Cinara spp. are typically purple to black and have antennae that are shorter than half the body length. Some species have a grey or white powdery wax covering their bodies. Both winged and wingless forms are produced, but wingless forms are observed more frequently. The aphids have piercing-sucking mouthparts, feed on phloem, and produce copious amounts on honeydew that promotes growth of sooty mold.
Quick Facts
- Cinara spp. are aphids that feed on coniferous trees and are sometimes found in Christmas tree nurseries. They are a nuisance pest in residential landscapes but can become problematic in years with significant precipitation.
- These aphids occur in groups and are relatively large when compared with other aphid genera. They also produce honeydew, which can cause sooty mold growth and causes needles to turn black. High populations of Cinara spp. can cause yellowing of foliage.
- Maintaining populations of resident natural enemies will help suppress aphid populations outdoors.
Giant conifer aphids (Cinara spp.) on juniper twig. These aphids only feed on conifers and are relatively large compared to most other aphid genera. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Infestation of giant conifer aphids on blue spruce. Image credit: Bob Hammon, Colorado State University, Bugwood.org
Eggs of giant conifer aphid. Image credit: William M. Ciesla, Forest Health Management International, Bugwood.org
Feeding injury on hedge caused by giant conifer aphids. Note the discoloration on the foliage. Image credit: William M. Ciesla, Forest Health Management International, Bugwood.org
Cypress tree with feeding injury caused by giant conifer aphids. Image credit: William M. Ciesla, Forest Health Management International, Bugwood.org
Life history and habits
Giant conifer aphids reproduce asexually through parthenogenesis, which allows their populations to build rapidly under favorable environmental conditions when natural enemies are sparse or absent. The last summer generation of giant conifer aphids lay eggs, which overwinter on the bark or needles of host trees. Nymphs emerge the following spring and molt through several instars until reaching adulthood. Generally, Cinara spp. populations are highest in late spring and decline by early summer. Multiple generations are produced each year.
Cinara spp. feed on roots, branches, or foliage, and tend to be found in large groups. They are host-specific, with most species feeding on a single species or genus of tree. As aphids feed, they excrete a sugar-rich waste – honeydew, which facilitates sooty mold growth and is often more problematic than the direct feeding injuries caused by the aphids. Honeydew is also attractive to ants and wasps, and ants will often protect the aphids from their natural enemies in exchange for honeydew. During cooler weather, Cinara spp. are typically more abundant on the lower trunk and branches.
Injury
These aphids are most likely to cause problems during the growing season following a mild winter. Trees can often tolerate some aphid feeding with little negative effects on plant health, and aphid populations are often allowed to build before any noticeable injury occurs. Therefore, early detection is important for effective management. These aphids tend to first appear in the lower crown. High densities of Cinara spp. can cause yellowing of foliage and stunted tree growth on young trees. However, needle discoloration can also be observed on trees infested with other sucking insects or infected with certain pathogens and is not a reliable indicator that aphids are present.
The presence of honeydew on trees is a good indication of aphid infestation, as is sooty mold growth, which causes needles to turn black. These aphids may also be present in Christmas tree nurseries and can subsequently be transported indoors. While these aphids are strictly a nuisance pest in the home, they can stain fabric when squished.
Monitoring
Trees can be inspected for honeydew or the growth of sooty mold, which often appears as black needles. Upon close inspection, groups of these aphids may be observed on foliage, twigs, branches, or the trunk. Aphids may become dislodged and drop off Christmas trees when being transported indoors.
Prevention
Providing susceptible trees in urban areas with good growing conditions can help prevent significant feeding injury. Injuring roots mechanically or through soil compaction should be avoided.
Cultural control
Aphids can be dislodged from plants with a high-pressure water stream. To be effective, this approach needs to be repeated frequently throughout the growing season.
Biological control
When present, natural enemies such as ladybeetles, lacewings, syrphid flies, and parasitic wasps, are often effective in suppressing aphid populations. Hosing off Christmas trees or wreaths with a strong water stream can help dislodge aphids before transporting the plant material indoors. Aphids can also be vacuumed when spotted on a tree or wreath.
Chemical control
In some instances, such as infestations on nursery plants, chemical control may be warranted. Applying systemic insecticides in the spring can help maintain low aphid populations throughout the growing season. Spraying a mixture of water with 2% dishwashing detergent or insecticidal soap when aphid populations are low can provide some control and have a low impact on non-target organisms.
References
Baker, J. 2019. Giant Conifer Aphids. North Carolina State University – Extension Available https://content.ces.ncsu.edu/giant-conifer-aphids
Cranshaw, W. 2019. Colorado State University – Extension. Available https://extension.colostate.edu/topic-areas/insects/aphids-on-shade-trees-and-ornamentals-5-511/
USDA. 2002. Spruce and Giant Conifer Aphids. United States Department of Agriculture. Available https://play.google.com/books/reader?id=896g6FsIIrUC&pg=GBS.PP6&hl=en
USDA. 2011. Giant Conifer Aphids. United States Department of Agriculture – Forest Health Protection. Available https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5350725.pdf
USU. (n.d.). Giant Conifer Aphids. Utah State University – Extension. Available https://extension.usu.edu/pests/ipm/ornamental-pest-guide/arthopods/aphids-adelgids/giant-conifer-aphids
Waldvogel, M. 2017. Cinara Aphid – Early Christmas Visitors. Available https://entomology.ces.ncsu.edu/2020/11/cinara-aphid-nuisance/