Many gardeners are familiar with the little green soft bodied insects that feed on the growing tips and flowers of many of their favourite garden plants. Aphids however are actually a very large and diverse group of insects with between 4,000-5,000 species worldwide. They come in a range of colours including green, black, brown, red, yellow, purple, gray and white. Size wise they vary in length between 1-10 mm. Some aphid species are wingless, some have wings, and some species have both winged and wingless members. Some species are attended by ants and others are not (attended by means that ants protect the aphids, in exchange they feed on the honey dew excreted by the aphids). Some species are host specific like rose aphids who only feed on roses. Others are generalists and feed on a variety of plant hosts. Some require 2 plant species to complete their life cycle, such as the potato aphid, that feeds on potato plants throughout the summer, reproducing non-sexually; but in the fall they move to rose bushes to reproduce sexually and lay their eggs that will overwinter till spring. Some species are shiny, some matt, some with mottling or distinct markings and some are even covered in waxy white secretions. There are even species that live in the soil feeding on plant roots. For and excellent website about aphids that lays out 200 genera of aphids complete with descriptions and photos visit https://influentialpoints.com/Gallery/Aphid_genera.htm

Some of the favoured plants aphids like to feed on are Asters, Cosmos, Dahlia, Larkspur, Hollyhocks, Mums, Nasturtium, Petunias, Roses, Tuberous begonia, Verbena, Zinnia, Rockcress, English daisy, Heuchera, Chrysanthemum, large-flowering Dahlia, Hydrangea, Mandevilla vines, Mustard and Horseradish.

Some Common Aphid Characteristics

In spite of all the variation between species there are plenty of characteristics that are more or less typical in aphids.

• They are soft bodied insects.
• Their bodies are typically pear shaped.
• They are small insects.
• They have 2 long antennae.
• They have 2 cornicles located at the posterior end of their abdomen that can release special pheromones which when released serve to alarm the other aphids of danger.
• The flightless females give birth to live young which look like the adults only smaller.
• Typically, once the eggs hatch in spring the aphids reproduce parthenogenetically (without males) until fall (in temperate zones) at which point they produce males and reproduce sexually and lay their eggs to over winter.
• Aphids feed by inserting their stylet into the plant and sucking out the plant juices causing yellowing, distortion, stunting and weakening of the plant.
• Aphids are notorious vectors of many plant viruses including cucumber mosaic virus, tobacco mosaic virus and about 150 others.
• Their bodies are fairly transparent.
• Aphids excrete a sticky substance called “honeydew” out their anus. This honeydew attracts ants, wasps and flies who feed on the substance. The honeydew is also prone to growing black sooty mold.
• Female aphids have a ovipositor for inserting their eggs into plants material.
• Aphids have 3 pair of long, skinny, jointed legs. One on each segment of their thorax.
• Aphids have many predators including lady beetles, lacewings, minute pirate bugs, syrphid flies and more. To read more about these predators check out my article 20+ Beneficial Insects for Home Gardens, Green Houses, Crops and Orchards

Some Species of Aphids and Their Preferred Plant Hosts

•  Potato aphid (Macrosiphum euphorbiae) varies in appearance from yellow green to pink. They feed on potatoes, peppers, tomatoes, eggplant, morning glory and occasionally lettuce and celery during the summer then fly to nearby rose canes in the fall, to mate sexually and lay their eggs to overwinter.
• Buckthorn-potato aphid (Aphis nasturtii) is lemon-yellow to green in colour. It feeds on potato plants during the summer then moves to buckthorn in the fall to feed, reproduces sexually and lays its eggs to overwinter. Buckthorn aphid is a vector of potato virus Y.
• Oleander aphid (Aphis nerii) are yellow in colour and feed on a wide range of hosts including milkweeds, oleander, periwinkle and other member of the dogbane family as well as mandevilla vines, sweet pepper nerium and members of the aster and bindweed families
• Soybean Aphid (Aphis glycines) are a pale-yellow green in colour. They feed on soybean during the summer and also lays it’s eggs on buckthorn to overwinter.
• Wooly apple aphid (Eriosoma lanigerum) are reddish brown or purple in colour. They feed on wild and cultivated apple trees, pear trees, oak, elm, ash, elder and hawthorn trees. 
• Green apple aphids (Aphis pomi) are a bright green colour. They feed on apple and pear trees, crabapple, hawthorn, mountain ash, spirea, quince and fire thorns (pyracantha).
• Rosy apple aphid (Dysaphis plantaginea (Passerini)) are brownish green to black in colour. They feed on apple, pear and hawthorn. 
• Black cherry aphid (Myzus Cerasi) are shiny black in colour. They feed on members of the mustard family during the summer and then moves to cherry trees in the fall to feed, reproduce sexually and lay their eggs.
• Giant Bark Aphid (Longistigma caryae) are gray in colour. They feed on oak, willow, hickory, pecan, hickory, maple, linden, elm, birch, walnut, golden rain tree and sycamores.
• Green peach aphid (Myzus persicae (Sulzer)) varies in color from yellowish green to rose pink. They feed on hundreds of different plants including aster, dahlia, verbena, petunias, iris, potato, pepper, spinach, asparagus, lettuce, celery and cabbage.
• Brown ambrosia aphids (Uroleucon rudbeckiae) are shiny red, reddish brown or blackish brown in colour. They feed on many members of the Asteraceae family including Ambrosia, Asters, coneflower, Achillea, Rudbeckia, sunflower, Coreopsis, Rudbeckia, Solidago and others.
• Spirea aphid (Aphis spiraecola) are bright greenish yellow to apple green in colour. They feed on over 65 plant genera but prefer Spirea and Citrus.
• Large Raspberry aphids (Amphorophora agathonica and Amphorophora sensoriat) feed on raspberry. “Amphorophora agathonica is of a yellow-green colour, A. sensoriata is pale bluish-green” (OMAFRA,© (2009)).
• Melon aphids (Aphis gossypii) are dark green aphids with red eyes. They feed on a variety of plants, especially cucurbits such as watermelon, cucumbers, cantaloupes, squash, pumpkin, as well as hibiscus, aster, hollyhock, lily, petunias, pepper, asparagus, pepper, okra, eggplant, citrus and cotton.
• Wooly Alder Aphid (Paraprociphilus tessellatus) are gray to black in colour. They feed on alder and silver maple.
• Cannabis aphid (Phorodon cannabis) are light cream to pale yellow color in early season. Later in the season their colouring becomes more variable ranging from light green to pale pink, to light brown. They feed on cannabis.
• Sunflower aphid (Aphis helianthi (Monell)) feeds on sunflowers and celery.
• Foxglove aphid (Aulacorthum Solani) vary in colour from light yellow green to dark green or brownish. They feed on a broad host range including foxglove, potato, tomato, peppers, cucumbers, lettuce, celery, chervil, pea, red and white clover and others. Foxglove aphids are a vector for lettuce mosaic virus and other viruses.
• Brown citrus aphid (Toxoptera citricida (Kirkaldy) nymphs are grey or reddish-brown in colour maturing to a shiny-black colour. They feed on citrus. Brown citrus aphid is a vector for citrus tristeza closterovirus (CTV).
• Black citrus aphid (Toxoptera Aurantii) are shiny black, brownish-black or reddish brown in colour. They feed on more than 120 plant species including citrus, cocoa, coffee, Hibiscus, maize, Vanda orchids and tea (Jackson G., (2020)).
• Cabbage aphids (Brevicoryne brassicae) are usually a whitish grey in color but occasionally black. They feed only on cruciferous plants like cabbage, cauliflower, bok choy, kale, broccoli, brussels sprouts and mustard plant.
• Woolly oak aphids (Stegophylla brevirostris (Quednau) and Diphyllaphis microtrema (Quednau) feed on various species of oak. Stegophylla brevirostris are a common pest appearing light green in colour and covered in a white wooly wax. Diphyllaphis microtrema are rare.
• White pine aphids (Cinara strobi) are a dull metallic grey colour. They feed on Eastern white pine and scotch pine.
• Root aphids are white in colour. There are several species of root aphids including:
  • Sugar beet root aphid (Pemphigus populivenae) feeds on sugar beet roots in the summer and moves to cotton wood and poplar trees in fall to lay their eggs in the bark crevices.
  • Rice root aphid
    • (Rhopalosiphum rufiabdominale) feed on members of the Rosaceae, Poaceae, and Solanaceae families.
    • R. rufiabdominale is universally associated with Prunus species but also infests various field crops, greenhouse vegetables, cannabis, and other ornamental plants.
    • (Rhopalosiphum abdominalis) feed on various grasses, including wheat and barley.
  • Auricula-root aphid (Pemphigus auriculae) mainly feed on plants in greenhouses and potted plants in homes but will also feed on outdoor primulas. 
  • Lettuce root aphid (Pemphigus bursarius) feed on lettuce and chicory and other members of the Compositae family during the summer then fly to poplar trees in the fall to feed on the leaf stalks, mate and lay their eggs in the galls that are produced by their feeding and overwinter.

Managing Aphid Populations

1. Ease up on nitrogen fertilizers, especially quick release types. Aphids are attracted to the quick flush of soft new growth it creates.
2. Apply dormant oil sprays to woody plants in early spring before their buds expand. This serves to suffocate overwintering eggs.
3. Aphids can be washed off the infected plants with a strong jet of water.
4. Aphids can be hand squashed.
5. Aphids have many predators such as ladybugs, green lacewings, big eyed bug, damsel bugs, pirate bugs and more. For information on how to attract these beneficials to your gardens visit 20+ Beneficial Insects for Home Gardens, Green Houses, Crops and Orchards
6. Aphids are repelled by the powerful scents of many herbs such as coriander, basil, chives, dill, peppermint, clove, rosemary, and thyme and flowers like marigolds and catnip. These plants make good companion plants for your more vulnerable plants.
7. Aphids like the colour yellow and are attracted to yellow sticky traps.
8. Insecticidal soap (either homemade or store bought) can be sprayed directly on the aphid colony. This serves to suffocate the aphids.

Summary

Aphids occur abundantly around the globe, especially in temperate zones. They are a serious pest to many cultivated plants. Their ability to reproduce without males and to produce only females until the autumn, allows them to build up large populations in a very short time. In addition to the feeding damage they cause, they are vectors of many viral diseases. Researchers estimate that between 25% to 50% of all viral plant diseases are caused by aphids. Learning to recognize the many faces of an aphid will assist you in your monitoring for this serious pest. Monitoring and early control are key steps to preventing large colonies of aphids.

Photo credits: all photos by the author.

Updated on July 2, 2022

References:

Alston D., (2016). Tree Fruit Aphid Biology & Management. https://extension.usu.edu/pests/files/slideshows/insects-tree-small-fruit/tree-fruit-aphid-2016.pdf

Corky’s Pest Control, (n.d.). APHID IDENTIFICATION WHAT’S AN APHID? https://www.corkyspest.com/aphid-id.html#:~:text=Different%20Types%20of%20Aphids%3A%20There%20are%20more%20than,feeds%20in%20clusters%2C%20preferring%20new%2C%20more%20succulent%20growth.

Gov. of Canada, (n.d.) rev. 2013-06-04. Aphids. https://www.canada.ca/en/health-canada/services/pest-control-tips/aphids.html

Influential Points,© (n.d.). Aphid Identification characteristics of genera. https://influentialpoints.com/Gallery/Aphid_genera.htm

Influential Points,© (n.d.). Aphid Biology and Morphology (Hemiptera: Aphidomorpha) Aphid Families and Subfamilies. https://influentialpoints.com/aphid/Aphidomorpha_subfamilies.htm

Jackson G., (2020). Citrus aphids (249). Pacific Pests, Pathogens & Weeds – Fact Sheets. https://apps.lucidcentral.org/ppp_v9/text/web_full/entities/citrus_aphids_249.htm#:~:text=The%20brown%20citrus%20aphid%20%28Toxoptera%20citricida%29%20occurs%20on,cocoa%2C%20coffee%2C%20Hibiscus%2C%20maize%2C%20Vanda%20orchids%20and%20tea.

Koppert Canada Limited, (n.d.) Aphids. https://retail.koppert.ca/pages/aphids#:~:text=Aphids%20form%20a%20single%2C%20very%20large%20group%20of,This%20means%20that%20populations%20can%20grow%20very%20quickly.

OMAFRA,© (2009). Aphids. Ontario Crop IPM. Raspberries. http://www.omafra.gov.on.ca/IPM/english/raspberries/insects/aphids.html

OMAFRA, (n.d.). Potato Ahids. Ontario Crop IPM. http://www.omafra.gov.on.ca/IPM/english/potatoes/insects/aphid.html

Ontario Ministry of Natural Resources, (1991). Common Pests of Trees in Ontario. http://woodsite.ca/wp-content/uploads/2014/09/Common_Pests_of_Ontario_s_Trees.pdf

RHS, (n.d.). Rose Aphids. https://www.rhs.org.uk/biodiversity/rose-aphids

Wikpedia and McGill university, (2007). Aphids. 2007 Schools Wikipedia Selection. https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/a/Aphid.htm

Wikpedia, (n.d.) rev. 26 July 2021. Aphididae. https://en.wikipedia.org/wiki/Aphididae

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